The ACHILLES team have been publishing quite prolifically. Since 2010 we have published more than 100 papers on a range of subjects related to the deterioration of infrastructure earthworks and the impact on transport infrastructure networks.
Below is a reference list of these publications. We are currently working on a narrative that shows the developments in our research and the evolution of scientific thought related to climate change impacts on long-linear infrastructure. We will post this as soon as these become available.
Some recent examples are shown below. Further down we have collated our publications relevant to ACHILLES. We will gradually update and expand these pages and will provide download links to the documents where we can. The names of the ACHILLES team members are shown in bold.
Armstrong, J., Preston, J., Helm, P., & Svalova, A. (2021). ACHILLES: Reducing earthworks failure risks and whole-life costs. Proceedings of the 3rd International Railway Symposium, Aachen, Germany, 21st – 23rd November, pp. 314–333. https://doi.org/10.18154/RWTH-2022-01713
Abstract: Vital transport and other linear infrastructure in Britain and elsewhere depends upon an extensive set of earthworks of varying age, condition and engineering quality. These earthworks are subject to normal deterioration, and these processes are exacerbated and complicated by the variable and unpredictable effects of climate change on weather patterns, particularly in the form of increased rainfall intensity and flooding. Railway earthworks are particularly vulnerable to these effects, given their typical age and the comparatively primitive engineering techniques used in their design and construction, as well as the increasing (pre-Covid) traffic levels to which they have been subjected. This paper describes research work being undertaken to improve the understanding of earthworks condition, deterioration and remediation, and to develop methods and tools to assist with the economic assessment of, selection from and prioritisation of alternative design interventions.
Armstrong, J. and Preston J. (2022). ACHILLES: The benefits and costs of increased asset information. Proceedings of The Fifth International Conference on Railway Technology: Research, Development and Maintenance, 22-25 August 2022, Montpellier, France.
Abstract: The ACHILLES research programme is providing improved understanding of earthworks’ deterioration mechanisms, of earthworks’ performance, with and without engineering interventions, and of the associated lifecycle cost implications. It is also developing decision support methods to inform intervention strategies and reduce whole-life costs. One of the novel aspects of ACHILLES is that it looks beyond the direct costs and benefits of the deterioration of assets and their remediation to consider the indirect costs and benefits of the various existing and potential sources of data and information on earthworks condition, on the safety, engineering and wider social implications of earthworks failures, and on the engineering and general social impacts of preventive measures to improve earthworks condition. The aim of this aspect of the work is to maximise the ratio of the benefits (safety, engineering and social) obtained from the data to the costs incurred in its collection and analysis. This aspect of ACHILLES is based upon the review of current and potentially available sources of data on earthworks condition, remediation costs and the impacts and benefits of earthworks failures and reactive/proactive interventions. The costs of obtaining and processing different data sources are compared with their potential accuracy, and their contribution to understanding and overall benefits. The work aims for generality where possible, but also takes account of the situation- and location-specific influences on failure and intervention costs.
Ball, J, Chambers, J., Wilkinson, P, Binley, A. (2022). Resistivity imaging of river embankments: 3D effects due to varying water levels in tidal rivers. Near Surface Geophysics, Vol. 21, Issue 1. https://doi.org/10.1002/nsg.12234
Abstract: Electrical resistivity tomography (ERT) has seen increased use in the monitoring the condition of river embankments, due to its spatial subsurface coverage, sensitivity to changes in internal states, such as moisture content, and ability to identify seepage and other erosional process with time-lapse ERT. Two-dimensional ERT surveys are commonly used due to time and site constraints, but they are often sensitive to features of anomalous resistivity proximal to the survey line, which can distort the resultant inversion as a three-dimensional (3D) effect. In a tidal embankment, these 3D effects may result from changing water levels and river water salinities. ERT monitoring data at Hadleigh Marsh, UK, showed potential evidence of 3D effects from local water bodies. Synthetic modelling was used to quantify potential 3D effects on tidal embankments. The modelling shows that a 3D effect in a tidal environment occurs (for the geometries studied) when surveys are undertaken at high water levels and at distances less than 4.5 m from the electrode array with 1 m spacing. The 3D effect in the modelling is enhanced in brackish waters, which are common in tidal environments, and with larger electrode spacing. Different geologies, river water compositions, and proximities to the model parameters are expected to induce a varied 3D effect on the ERT data in terms of magnitude, and these should be considered when surveying to minimize artefacts in the data. This research highlights the importance of appropriate geoelectrical measurement design for tidal embankment characterization, particularly with proximal and saline water bodies.
Blake A, Smethurst J, Yu Z, Brooks H, Stirling R, Holmes J, Watlet A, Whiteley J, Chambers J, Hughes P, Smith A, Briggs KM. (2022). Long-term monitoring of long linear geotechnical infrastructure for a deeper understanding of deterioration processes. 11th International Symposium on Field Monitoring in Geomechanics, London, UK, 4th – 8th September. https://doi.org/10.57711/f73d-pf35
Abstract: Long linear geotechnical infrastructure such as earth embankments and cuttings used for railways, highways and flood defence can progressively reduce in performance over time as a result of aging and deterioration principally driven by environmental cycles of wetting and drying. These include volumetric and fabric changes including desiccation cracking, accumulating downslope plastic strain and geo-chemical/mineralogical changes, influencing the strength, stiffness, permeability and water retention behaviour of the soils from which they are constructed. A deeper understanding of these processes is necessary to develop effective tools for assessing and forecasting the geotechnical condition of long linear infrastructure over the lifespan of the asset and in response to climate change. As part of a major research project called ACHILLES, three exemplar long linear geotechnical earthworks have been instrumented with state-of-the-art sensors for long-term monitoring of deterioration behaviour and condition. The monitored sites are a highway cutting slope, a constructed trial embankment and a flood embankment. The sites are also being extensively characterised using geophysical, geodetic, UAV and cone penetrometer approaches. Data from these exemplar assets is of fundamental importance to understanding deterioration processes and is being used to validate conceptual and numerical models of asset performance and enable rapid characterisation of their current condition.
Boyd, J., Chambers, J., Wilkinson, P., Meldrum, P., Merrit, A., Jones, L., Kirkham, M., Binley, A. (2019). Time-lapse electrical resistivity tomography as an aid in active slope stability assessment. EGU General Assembly 2019, Vienna, Austria, 7–12 April 2019. https://doi.org/10.3997/2214-4609.201902452
Summary: Landslides pose risks to both infrastructure and communities globally; mitigating these risks requires an understanding of susceptible geological materials and trigger mechanisms within landslides, and how these can change with time. Typically, site investigation of hazardous hillslopes involves discrete measurements to identify key mechanical parameters for the types of material present, but at low spatial resolutions. As a consequence slope stability modelling, which relies on these discrete measurements, does not always capture the full spatial or temporal complexity of the problem. Numerous studies have shown the benefit that geophysical techniques (e.g. geoelectrics, seismics) can bring to landslide site investigation, illuminating geometrical, mechanical and hydrological conditions of unstable hillslopes. Time-lapse electrical resistivity tomography (ERT) has been shown to be sensitive to changes subsurface in moisture content. Resistivity is readily related to water saturation using well established petrophysical relationships, which are of upmost interest given the majority of landslides are moisture induced. In this study we present the use of a geoelectrical monitoring system on an active landslide in Lias mudrocks, North Yorkshire, UK. Building on previous studies of the field site, subsurface resistivity distributions determined from time-lapse ERT are converted into shear strength estimates through appropriate calibration between moisture content, electrical resistivity and matrix suction in order to compute pore pressures. The ERT workflow is constrained by other data streams, such as a series of GPS surveys to track electrode movements on the hillslope, seasonal temperature corrections, digital elevation models (observed by laser ranging) and seismic refraction surveys. Shallow borehole and field samples are used to determine mechanical parameters (such as density, internal frictional angle) and petrophysical relationships. Preliminary results show agreement between decreases in ERT-derived shear strength estimates and real slope movements observed by tilt meters and LIDAR images. Given the development of dedicated time-lapse ERT systems, and the use of electrical resistivity as a proxy for moisture content, and by extension pore pressure, we suggest the basis for coupling time-lapse ERT with hydromechanical modelling for real time slope stability assessment.
Boyd, J., Chambers, J., Wilkinson, P., Uhlemann, S., Merritt, A., Meldrum, P., Swift, R., Kirkham, M., Jones, J., Binley, A. (2019). Linking Geoelectrical Monitoring to Shear Strength – A Tool for Improving Understanding of Slope Scale Stability. 25th EU Meeting of Environmental & Engineering Geophysics, The Hague, Netherlands, 8 – 12 September 2019. https://doi.org/10.3997/2214-4609.201902452
Summary: Landslides pose a risk to both infrastructure and wider society, managing the geohazard requires and understanding of factors driving slope instability, in particular the response to moisture content. Traditional methods of slope investigation involve discrete point geotechnical measurements which are not spatially sensitive. Recent studies have shown the spatial sensitivity of geoelectrical methods to both the internal geometry of unstable hill slopes and moisture dynamics, demonstrating their value in landslide investigation and characterisation. In this study we present the use of a geoelectrical monitoring system on an active landslide in Lias mudrocks, North Yorkshire, UK. Building on previous studies of the field site, subsurface resistivity distributions determined from time-lapse electrical resistivity tomography (ERT) are converted into shear strength estimates through calibration between electrical resistivity and matrix suction. Geotechnical parameters are determined from shallow borehole samples. Shear strength distributions show agreement with field observations of the slope, relatively low shear strength values (<100 kpa) correspond to the parts of the slope which are actively moving. We suggest there is scope for further work identifying regions of potentially instability on hillslopes through coupled hydromechanical and geoelectrical modelling.
Boyd, J., Holmes, J., Wilkinson, P., Chambers, J., Binley, A. (2019). Long-term geoelectrical monitoring for unstable slopes: challenges and opportunities for slope stability modelling. New Advances in Geophysics 2019, London, UK
Boyd, J. P., Chambers, J., Wilkinson, P., Watlet, A., Holmes, J. and Binley, A. (2021). Linking field electrical resistivity measurements to pore suction and shear strength, for improved understanding of long term landslide stability. 33rd Symposium on the Application of Geophysics to Engineering and Environmental Problems, SAGEEP 2021, online, 14th – 19th March. https://doi.org/10.4133/sageep.33-078
Abstract: The mechanical properties and the level of pore water saturation within a slope contribute to its stability; changes in these parameters, like an increase in saturation, can trigger a landslip. Conventional discrete point sampling methods are used to measure crucial mechanical and hydrological properties, but often lack the spatial resolution required to capture the full complexity of the problem. Geophysical methods, such as electrical resistivity tomography (ERT), are spatially sensitive to relevant subsurface properties. Electrical resistivity is related to the moisture content through well understood petrophysical relationships; consequently, recent studies have successfully explored the use of ERT to monitor saturation levels with geoelectrical monitoring. In such applications, repeated surveys (e.g. with a permanently installed measurement system) allow time-lapse tomographic images of the subsurface to be constructed. This is of particular interest given that the majority of landslides are induced by changes in pore pressure due to rainfall infiltration. We present the use of a geoelectrical monitoring system on an active landslide in Lias mudrocks, North Yorkshire, UK. Subsurface resistivity distributions determined from time-lapse ERT are converted into pore suction estimates through direct laboratory calibration between moisture content, electrical resistivity and matrix suction. A custom time-lapse ERT workflow has been developed to account for slope movements during the monitoring period. GPS markers, which cover the extent of the monitoring array, are used to infer slope movements and changing electrode positions. Field samples are recovered from shallow boreholes for mechanical testing and petrophysical relationships are developed, such that shear strength can be estimated from the ERT models. Decreases in ERT-derived pore suction (and hence shear strength) are observed prior and during slope movements measured by infield accelerometers. Given the development of dedicated time-lapse ERT systems, and the use of electrical resistivity as a proxy for suction and saturation, we suggest the use of ERT monitoring as an input for slope-scale stability monitoring.
Briggs, KM, Dijkstra, TA and Glendinning, S (2019). Evaluating the Deterioration of Geotechnical Infrastructure Assets Using Performance Curves. In International Conference on Smart Infrastructure and Construction 2019 (ICSIC) Driving data-informed decision-making (pp. 429-435). ICE Publishing. [link]
Abstract: Long Linear (geotechnical) Assets (LLAs) are a major component of the physical infrastructure required to deliver critical services over long distances. This existing, physical transport infrastructure is at various stages of performance and deterioration, some of which is in a poor state or reaching the end of life. This paper describes a framework for understanding deterioration processes and then evaluates the use of curves to map the performance of LLAs forming the UK’s transport infrastructure network. Detail was added to generic performance curves by considering the peer-reviewed evidence for the drivers, properties and mechanisms causing a loss of soil strength in transport infrastructure embankments. The results show that performance curves can be used to evaluate the performance of LLAs over their lifetime, to consider specific definitions of performance and to compare asset types. They provide a common language to communicate the deterioration mechanisms affecting assets or a network of assets. They provide a method to structure the planning, collection and interpretation of large volumes of ‘smart’ information describing the performance of long linear assets. This contributes to the UK’s infrastructure vision to deliver intelligent design, management and maintenance.
Briggs, K.M., Loveridge, F.A. and Glendinning, S., (2017). Failures in transport infrastructure embankments. Engineering Geology, 219, pp.107-11
Abstract: To ensure that road and rail transport networks remain operational, both highway and railway embankments require continual maintenance and renewal to mitigate against ongoing deterioration and repair any sections damaged by realised failures. This paper provides a review of recent developments in the understanding of highway and railway embankment degradation and failure. Failures due to pore water pressure increase, seasonal shrink-swell deformation and progressive failure are considered. The material composition and construction of highway and railway embankments differ, which influences the dominant type and timing of embankment failure. There is evidence for highway embankment failures induced by pore water pressure increase, but not seasonal deformation and progressive failure. Some railway embankments are susceptible to pore water pressure increase, seasonal shrink-swell deformation and progressive failure due to the age and nature of the dumped clay fill used in their construction. The approaches used to measure and explore embankment failure mechanisms are compared and discussed. Field observations have been used to understand pore water pressure increase and seasonal shrink-swell deformation in embankments, while the investigation of progressive embankment failure has mainly utilised physical and numerical modelling approaches. Further field and laboratory investigation is required before the rigorous analysis of embankment failure can be routinely undertaken. However, progress is being made to empirically identify and evaluate the various risk factors affecting transport infrastructure embankment failure.
Briggs, K., Blackmore, L., Svalova A., Loveridge F., Glendinning, S., Powrie, W., Butler, S., Sartain, N. (2022). The influence of weathering on index properties and undrained shear strength for the Charmouth Mudstone Formation of the Lias Group at a site near Banbury, Oxfordshire, UK. Quarterly Journal of Engineering Geology and Hydrogeology, Vol. 5. https://doi.org/10.1144/qjegh2021-066
Abstract: The Lias outcrop extends continuously from Dorset to Yorkshire in England, with outlying areas in Somerset and Wales. It underlies the transport routes between a number of major UK cities. Understanding the material properties of the Lias Group is therefore important for infrastructure construction and maintenance across England and Wales. This study examines the influence of weathering on the engineering properties of the Charmouth Mudstone Formation (Lias Group) in light of recent developments in ground-investigation practice including: (i) the use of modern visual weathering classifications for soils and rocks; and (ii) the availability of large ground-investigation datasets from the construction of the High Speed Two (HS2) railway. The variability in the undrained shear strength data was consistent with the moisture content, liquidity index and plasticity index of the samples, but they were poorer indicators than shown in previous studies. The visually-assessed weathering class and the depth below ground level were found to be more useful indicators of the undrained shear strength of the clay and mudstone samples of the Charmouth Mudstone Formation.
Brooks H, Stirling R, Blake A, Dijkstra T, Glendinning S, Holmes J, Yu Z, Watlet A, Whiteley J, Briggs K, Smith A, Hughes P, Smethurst J, Chambers J, Dixon N. (2022). Climate-driven impacts on flood embankment deterioration. 16th BGA Young Geotechnical Engineers Symposium, Newcastle upon Tyne, UK, 4th – 5th July 2022.
Brooks H, Stirling R, Blake A, Holmes J, Yu Z, Watlet A, Whiteley J, Briggs K, Smith A, Hughes P, Smethurst J, Chambers JE, Dixon N. (2022). Climate-driven deterioration of long-life, long-linear geotechnical infrastructure. EGU General Assembly 2022, Vienna, Austria, 23rd – 27th May. https://doi.org/10.5194/egusphere-egu22-13409
Summary: Long-life, long linear geotechnical assets such as road, rail and flood embankments provide vital transport and flood defence infrastructure. Slope failures can close transport networks and cause delays, or can reduce the protection provided against flood hazards. This creates huge economic cost and can cause a risk to life for those using affected transport networks or resident on the floodplain. Where emergency repair is needed, the estimated cost of this is 10 times that of scheduled maintenance making effective asset management an industry priority (Glendinning et al., 2009). However, projected climatic changes pose a threat to the stability of these assets. The most recent IPCC report highlighted projected future changes to temperatures and rainfall. These climatic changes alter the natural cycles of wetting and drying experienced by assets, which results in deterioration of asset performance. Deterioration can occur due to a variety of processes, including crack formation and propagation, downslope plastic strain accumulation and geochemical or mineralogical changes. These ultimately influence the strength, stiffness, permeability and water retention of the soil, which can often mean the construction standard of the asset is not maintained (Stirling et al., 2021). The ACHILLES project aims to improve understanding of how these processes occur and how they may be affected by projected climatic change. Here, we introduce three large-scale field monitoring sites, including a purpose-built trial embankment, flood embankment and highway cutting. These assets are heavily instrumented to measure soil deformation, soil hydrology and local weather conditions, amongst others. Data from these sites are analysed to further understand deterioration processes and inform future design, construction, monitoring and management of these earthworks. We will discuss key insights from this project, including implications for stakeholders.
Clarkson, P., Crickmore, R., Godfrey, A., Minto, C., Chambers, J., Dashwood, B., Gunn, D., Jones, L., Meldrum, P., Morgan, D., Watlet, A. and Whiteley, J. (2021). Correlation between Distributed Rayleigh Sensing (DRS) and moisture sensors as indicators of slope instability. 27th European Meeting of Environmental and Engineering Geophysics, Held at Near Surface Geoscience Conference and Exhibition 2021, August 2021. https://doi.org/10.3997/2214-4609.202120110
Summary: This paper describes the verification of Distributed Rayleigh Sensing (DRS), traditionally associated with acoustic sensing, for monitoring low frequency activity on a slope prone to landslides that is used as the British Geological Survey’s landslide observatory at Hollin Hill, North Yorkshire, U.K. The observatory is monitored using a variety of geological survey instruments and provides a unique opportunity to compare measurement systems that have very different principles of operation. Previous studies of the slope have shown good correlation between the low frequency strain and temperature measured using the fibre with prior knowledge of the geology of the site and longer-term measurements made on more established geological survey instruments. This paper presents a more detailed comparison of measurements made on the DRS system over the winter of 2020/2021, with measurements of soil moisture content made on point sensors and estimates of ground movement measured using GPS marker posts. The DRS system is sensitive to multiple important indicators of slope instability and can monitor ground movement effectively. Areas of unstable ground can be clearly identified by the larger changes observed in the fibre output in those regions.
Chambers, J. (2019). Electrical imaging methods in geotechnical applications: From site investigation to near-real-time monitoring and decision support. 7th International Symposium on Deformation Characteristics of Geomaterials, Glasgow, UK, 26–28 June 2019 (Keynote)
Chambers, J. (2022). Development of geoelectrical imaging for the remote condition monitoring of engineered structures. First workshop on NDT, CM and SHM requirements for civil structures. Institution of Civil Engineers, London, UK.
Chambers J., Boyd J., Novellino A., Jordan C., Biggs J., Selvakumaran S., Hooper A., Wright T. (2021). Using corner reflectors for enhancing landslide and infrastructure monitoring in the UK. EGU General Assembly 2021, online, 19-30 April. https://doi.org/10.5194/egusphere-egu21-5133
Summary: We present InSAR results of the Hollin Hill landslide where a variety of ground-based geophysical measurements (e.g. GPS, Electric resistivity tomography, meteorological observations) are available for comparison with InSAR data. We use Sentinel-1 InSAR data acquired between Oct 2015 and Jan 2021 to study the behaviour of this landslide. We find that the Line of Sight component of the down-slope movement is 2.7 mm/yr in the descending track, and 7.5-7.7 mm/yr in the ascending track. The InSAR measurements also highlight the seasonal behaviour of this landslide. In July 2019 six corner reflectors were installed to improve the coherence of the InSAR measurements, especially in the ascending acquisition mode. We present comparison with ground-based measurements such as the movement recorded by the GPS measurements of the pegs of the ERT survey or the moisture recorded by the various instruments at the site, and show the improvement introduced by the corner reflectors. In addition we present results of an experiment that explores the use of smaller corner reflectors for potential urban applications of infrastructure monitoring. A single corner reflector needs to be at least ~67cm wide and tall to be seen by the Sentinel-1 satellites. We show that by placing 4 reflectors with 33cm dimensions in the same pixel coherent signal can be acquired. It is feasible to install small reflectors on bridges, tall buildings, or incorporate “corner-like” features in newly built structures,but care needs to be taken on the precise spacing of the reflectors to avoid destructive interference. Continuous monitoring of infrastructure with remote sensing and machine learning can alert to potential failures where further investigation is needed.
Chambers J, Holmes J, Whiteley J, Boyd J, Meldrum P, Wilkinson P, Kuras O, Swift R, Harrison H, Glendinning S, Stirling R, Huntley D, Slater N, Donohue S. (2022). Long-term geoelectrical monitoring of landslides in natural and engineered slopes. The Leading Edge, 41(11), pp. 742–804. https://doi.org/10.1190/tle41110768.1
Abstract: Developments in time-lapse electrical resistivity tomography (ERT) technology are transforming our ability to monitor the subsurface due to purpose-built monitoring instruments, advances in automation and modeling, and the resulting improvements in spatial and temporal resolution. We describe the development of a novel ERT-based remote monitoring system called PRIME that integrates new low-power measurement instrumentation with data delivery, automated data processing and image generation, and web-based information delivery. Due to the sensitivity of ERT to hydrologic processes in the near surface, we focus on the application of PRIME for moisture-driven landslide monitoring. Case examples are considered of landslides in engineered and natural slopes, including those impacting geotechnical assets in rail and highways, where slope hydrology is seen to be controlled by lithology, vegetation, fissuring, and drainage structures. We conclude by taking a forward look at emerging developments in ERT monitoring relating to hardware, software and modeling, and applications.
Chambers, J., Meldrum, P., Wilkinson, P., Gunn, D., Watlet, A., Dashwood, B., Whiteley, J., Harrison, H., Swift, R., Inauen, C., Kuras, O., Jessamy, G., Glendinning, S., Clarkson, P., Minto, C., Godfrey, A. and Crickmore, R. (2021). Geophysical remote condition monitoring of transportation infrastructure slopes. 2nd Conference on Geophysics for Infrastructure Planning, Monitoring and BIM, Held at Near Surface Geoscience Conference and Exhibition 2021, April 2021. https://doi.org/10.3997/2214-4609.202120077
Summary: Here we consider the development and use of geophysical remote-condition-monitoring (RCM) solutions for monitoring slope stability, which have the advantage of providing spatial and volumetric subsurface information with the potential to identify the causal processes leading to slope failure. We illustrate geophysical RCM of transportation infrastructure and third party land, with examples from highways and rail, and with reference to the Hollin Hill Landslide Observatory (HHLO), which has been used to trial candidate technologies, to show the benefit of integrated geophysical-geotechnical monitoring approaches.
Chambers, J., Meldrum, P., Wilkinson, P., Inauen, C., Watlet, A., Swift, R., Whiteley, J., Harrison, H., Gunn, D., Kuras, O., Glendinning, S., Curioni, J., Jessamy, G. and Slater, N. (2021). Automated geoelectrical monitoring in support of infrastructure management and remediation. SEG Expanded Abstracts – First International Meeting For Applied Geoscience & Energy. https://doi.org/10.1190/segam2021-3584038.1
Abstract: The development and application of a novel low cost geoelectrical monitoring system is described. The system comprises measurement instrumentation designed for long-term deployment at field sites, telemetric control, automated data processing and modelling, and information delivery. System deployment for a range of scenarios is considered, including before, during and after remedial interventions for engineered earthworks and subsurface infrastructure.
Chambers, J, Meldrum, P, Wilkinson, P, Kuras, O, Gunn, D, Uhlemann, S, Swift R, Inauen, C, Watlet, A and Slater, N (2019). Novel Low-Power Autonomous Ground Imaging Technology for Geohazard Monitoring, Information Delivery and Decision Support. 81st EAGE Conference and Exhibition 2019, Jun 2019, Vol 2019, p.1 – 5. doi.org/10.3997/2214-4609.201901663
Summary: Here we present a comprehensive geophysical geohazard monitoring approach, built on geoelectrical imaging and encompassing novel monitoring instrumentation, automated data processing, and web-based information delivery. The approach is referred to as the PRIME (Proactive Infrastructure Monitoring and Evaluation) system. We describe the concept, and consider how it contributes to geohazard monitoring, forecasting and information delivery.
Chambers, J., Meldrum, P., Wilkinson, P., Whiteley, J., Watlet, A., Boyd, J., Holmes, J., Donohue, S., Gunn, D., Kuras, O., Swift, R., Harrison, H., Inauen, C., Uhlemann, S. and Kendall, J. (2021). Geophysical monitoring of natural and engineered slopes: Towards improved early warning of landslides. 17th Conference and Exhibition Engineering and Mining Geophysics, April 2021. https://doi.org/10.3997/2214-4609.202152175
Summary: Here we describe the development of geoelectrical monitoring approaches and their contribution to the landslide early warning systems. Our focus is site (or local) scale monitoring of moisture driven slope failure in soft rock environments.
Clarkson, P, Cole, S, Godfrey, A, Crickmore, R, Minto, C, Watlet, A, Whiteley, J, Chambers, J, Boyd, J, Dashwood, B. (2022). Verification of a distributed fiber optic sensing slope stability monitoring solution. 56th U.S. Rock Mechanics / Geomechanics Symposium, Santa Fe, New Mexico, USA, June 2022. https://doi.org/10.56952/ARMA-2022-0715
Abstract: This paper describes the testing of a novel ground condition and slope stability monitoring system based on Distributed Rayleigh Sensing (DRS) on a landslide observatory operated by the British Geological Survey (BGS). The DRS system uses the backscattered light from buried fiber optic cables to determine the strain and temperature at any point along the fiber up to distances of over 50 km and has been shown to respond to ground movement, moisture content changes and temperature variations. The output of the fiber is compared to that expected based on the known geology of the slope and other instruments such as tiltmeters and moisture content sensors. In addition to long-term strain and temperature measurements, the system can also sense acoustic vibrations and can be used to make active and passive seismic surveys to give a comprehensive 3D picture of the subsurface state. The results show that the DRS system can provide improved spatial and time resolution and sensitivity to give a more comprehensive and detailed picture of slope behavior than would otherwise be possible. Such detail allows improved landslide prediction methods and early warning systems to be developed.
Clarkson, P., Minto, C., Crickmore, R., Godfrey, A., Purnell, B., Chambers, J., Dashwood, B., Gunn, D., Jones, L., Meldrum, P., Watlet, A. and Whiteley, J. (2021). Distributed Rayleigh Sensing for Slope Stability Monitoring. 55th U.S. Rock Mechanics Geomechanics Symposium 2021, Houston, Texas, U.S., 20th – 23rd June 2023. [link]
Abstract: We present a novel approach to slope stability monitoring using a Distributed Rayleigh Sensing system on conventional, commercial fiber optic cables. Commercially this technology is generally deployed for characterising short time period strains or Distributed Acoustic Sensing (DAS) and is not usually considered for static strain monitoring. Advances in equipment and characterisation at ultra low frequencies tending towards 0 Hz provides a mechanism to record static strain from an arbitrary starting point together with local temperature and acoustic monitoring from a single instrument / fiber pair. By exploiting differences in cable characteristics we can extract each measurand from what would be a combined single measurand. The long range of Rayleigh based systems enables the linear monitoring of dams, levees and embankments over many miles. We describe a long term deployment at the UK’s National Landslip Laboratory with the British Geological Survey which experiences annual slips and correlate data from the purely glass sensor with those from other instrumentation.
Dixon, N., Crosby, C.J., Stirling, R., Hughes, P.N., Smethurst, J., Briggs, K., Hughes, D., Gunn, D., Hobbs, P., Loveridge, F., Glendinning, S., Dijkstra, T and Hudson, A (2019). In situ measurements of near-surface hydraulic conductivity in engineered clay slopes. Quarterly Journal of Engineering Geology and Hydrogeology, 52(1), pp.123-135
Abstract: In situ measurements of near-saturated hydraulic conductivity in fine-grained soils have been made at six exemplar UK transport earthwork sites: three embankment and three cutting slopes. This paper reports 143 individual measurements and considers the factors that influence the spatial and temporal variability obtained. The test methods employed produce near-saturated conditions and flow under constant head. Full saturation is probably not achieved owing to preferential and bypass flow occurring in these desiccated soils. For an embankment, hydraulic conductivity was found to vary by five orders of magnitude in the slope near-surface (0–0.3 m depth), decreasing by four orders of magnitude between 0.3 and 1.2 m depth. This extremely high variability is in part due to seasonal temporal changes controlled by soil moisture content, which can account for up to 1.5 orders of magnitude of this variability. Measurements of hydraulic conductivity at a cutting also indicated a four orders of magnitude range of hydraulic conductivity for the near-surface, with strong depth dependence of a two orders of magnitude decrease from 0.2 to 0.6 m depth. The main factor controlling the large range is found to be spatial variability in the soil macrostructure generated by wetting–drying cycle driven desiccation and roots. The measurements of hydraulic conductivity reported in this paper were undertaken to inform and provide a benchmark for the hydraulic parameters used in numerical models of groundwater flow. This is an influential parameter in simulations incorporating the combined weather–vegetation–infiltration–soil interaction mechanisms that are required to assess the performance and deterioration of earthwork slopes in a changing climate.
Grebby, S., Sowter, A., Gluyas, J., Toll, D., Gee, D., Athab, A. and Girindran, R., (2021). Advanced analysis of satellite data reveals ground deformation precursors to the Brumadinho Tailings Dam collapse. Communications Earth & Environment, 2(1), pp.1-9.
Abstract: Catastrophic failure of a tailings dam at an iron ore mine complex in Brumadinho, Brazil, on 25th January 2019 released 11.7 million m3 of tailings downstream. Although reportedly monitored using an array of geotechnical techniques, the collapse occurred without any apparent warning. It claimed more than 200 lives and caused considerable environmental damage. Here we present the Intermittent Small Baseline Subset (ISBAS) technique on satellite-based interferometric synthetic aperture radar (InSAR) data to assess the course of events. We find that parts of the dam wall and tailings were experiencing deformation not consistent with consolidation settlement preceding the collapse. Furthermore, we show that the timing of the dam collapse would have been foreseeable based on this observed precursory deformation. We conclude that satellite-based monitoring techniques may help mitigate similar catastrophes in the future.
Holmes, J., Chambers, J., Meldrum, P., Wilkinson, P., Boyd, J., Williamson, P., Huntley, D., Sattler, K., Elwood, D., Sivakumar, V. and Reeves, H., 2020. Four‐dimensional electrical resistivity tomography for continuous, near‐real‐time monitoring of a landslide affecting transport infrastructure in British Columbia, Canada. Near Surface Geophysics, 18(Geoelectrical Monitoring), pp.337-351. https://doi.org/10.1002/nsg.12102
Abstract: The Ripley Landslide is a small (0.04 km2), slow‐moving landslide in the Thompson River Valley, British Columbia, that is threatening the serviceability of two national railway lines. Slope failures in this area are having negative impacts on railway infrastructure, terrestrial and aquatic ecosystems, public safety, communities, local heritage and the economy. This is driving the need for monitoring at the site, and in recent years there has been a shift from traditional geotechnical surveys and visual inspections for monitoring infrastructure assets toward less invasive, lower cost, and less time‐intensive methods, including geophysics. We describe the application of a novel electrical resistivity tomography system for monitoring the landslide. The system provides near‐real time geoelectrical imaging, with results delivered remotely via a modem, avoiding the need for costly repeat field visits, and enabling near‐real time interpretation of the four‐dimensional electrical resistivity tomography data. Here, we present the results of the electrical resistivity tomography monitoring alongside field sensor‐derived relationships between suction, resistivity, moisture content and continuous monitoring single‐frequency Global Navigation Satellite System stations. Four‐dimensional electrical resistivity tomography data allows us to monitor spatial and temporal changes in resistivity, and by extension, in moisture content and soil suction. The models reveal complex hydrogeological pathways, as well as considerable seasonal variation in the response of the subsurface to changing weather conditions, which cannot be predicted through interrogation of weather and sensor data alone, providing new insight into the subsurface processes active at the site of the Ripley Landslide.
Holmes, J., Chambers, J., Wilkinson, P., Dashwood, B., Gunn, D., Cimpoiaşu, M., Kirkham, M., Uhlemann, S., Meldrum, P., Kuras, O., Huntley, D., Abbott, S., Sivakumar, V., Donohue, S. (2022). 4D electrical resistivity tomography for assessing the influence of vegetation and subsurface moisture on railway cutting condition. Engineering Geology, Vol. 307. https://doi.org/10.1016/j.enggeo.2022.106790
Abstract: Instability of slopes, embankments, and cuttings on the railway network is increasingly prevalent globally. Monitoring vulnerable infrastructure aids in geotechnical asset management, and improvements to transport safety and efficiency. Here, we examine the use of a novel, near-real-time Electrical Resistivity Tomography (ERT) monitoring system for assessing the stability of a railway cutting in Leicestershire, United Kingdom. In 2015, an ERT monitoring system was installed across a relict landslide (grassed) and an area of more stable ground on either side (wooded), to monitor changes in electrical resistivity through time and space, and to assess the influence of different types of vegetation on the stability of transportation infrastructure. Two years of 4-Dimensional ERT monitoring results are presented here, and petrophysical relationships developed in the laboratory are applied to calibrate the resistivity models in order to provide an insight into hydrogeological pathways within a railway cutting. The influence of vegetation type on subsurface moisture pathways and on slope stability is also assessed – here we find that seasonal subsurface changes in moisture content and soil suction are exacerbated by the presence of trees (wooded area). This results in shrink-swell behaviour of the clays comprising the railway cutting, resulting in fissuring and a reduction in shear strength, leading to instability. As such, it is proposed that on slopes comprised of expansive soils, grassed slopes are beneficial for stability. Insights into the use of 4-D ERT for monitoring railway infrastructure gained from this study may be applied to the monitoring of critical geotechnical assets elsewhere.
Holmes, J., Chambers, J., Wilkinson, P., Meldrum, P., Cimpoiaşu, M., Boyd, J., Huntley, D., Williamson, P., Gunn, D., Dashwood, B. and Whiteley, J., 2022. Application of petrophysical relationships to electrical resistivity models for assessing the stability of a landslide in British Columbia, Canada. Engineering Geology, p.106613. https://doi.org/10.1016/j.enggeo.2022.106613
Abstract: Landslides in the Thompson River Valley, British Columbia, Canada, threaten the serviceability of two railway lines that connect Vancouver to the rest of Canada and the US. To minimise the impact of slope instability on vital transport infrastructure, as well as on terrestrial and aquatic ecosystems, public safety, communities, local heritage, and the economy, and to better inform decision making, there is a need for monitoring. Since 2013, the Ripley Landslide – a small, slow-moving, translational landslide – has been the focus of monitoring efforts in the Thompson River Valley transportation corridor. In November 2017, a novel Electrical Resistivity Tomography (ERT) monitoring system was installed on the site, providing near-real-time data collection via a telemetric link. 4-Dimensional resistivity models are presented in the context of moisture content and soil suction, two parameters known to influence slope stability in the Thompson River Valley. Here, we discuss the development of laboratory-based petrophysical relationships that relate electrical resistivity to moisture content and soil suction directly, building on relationships developed in the field. The 4-D ERT models were calibrated using these petrophysical relationships to provide insights into the complex spatial and temporal variations in moisture content and soil suction. This study highlights the utility of geoelectrical monitoring for assessing slope stability in the context of moisture-driven landslides.
Holmes, J, Sivakumar, V, Wilkinson, P, Huntley, D, Chambers, J, Donohue, S. (2020). Assessing landslide risk using near surface geogphysics for the long term monitoring of a slope affecting transport infrastructure in western Canada. SAGEEP 2020 – 33rd Annual Symposium on the Application of Geophysics to Engineering and Environmental Problems, Denver, Colorado, 29th March – 1st April 2020. https://doi.org/10.4133/sageep.33-079
Abstract: The Ripley Landslide is a small (0.04 km2), slow moving, translational landslide, which threatens the integrity of two major railway lines in the Thompson River valley, British Columbia. This valley is a critical transportation corridor connecting Vancouver to other parts of Canada and the USA. In addition to damaging vital transport infrastructure, slope failure at this site would also negatively impact the economy, environment, salmon runs, potable water supply, public safety, culture and heritage. In order to monitor slope movement, to understand the processes that govern instability in this area, and to mitigate failure, a geophysical monitoring program commenced in 2013. Multiple geophysical methods were deployed on the site, including terrestrial-based Electrical Resistivity Tomography (ERT), Ground Penetrating Radar (GPR), Fixed Frequency Electromagnetic Induction (FEM), Seismic Refraction & Multichannel Analysis of Surface Waves (MASW), and waterborne ERT, GPR, FEM & Acoustic Bathymetry. This data was used to produce a 3-dimensional ground model of the site, providing insight into the lithological setting of the landslide. The focus of the geophysical investigation in recent years has been the long-term monitoring of a small section of the slope (crossing the head scarp of the landslide) using a Proactive Infrastructure Monitoring and Evaluation (PRIME) system, which uses a wireless connection to send ERT data to remote servers, producing near-real-time resistivity models for use in slope stability assessment. Here, the first year of monitoring data from the Ripley Landslide PRIME system is presented, alongside laboratory work, which has been undertaken to provide insight into the petrophysical relationships of the landslide materials. These relationships provide a direct link between resistivity, moisture content, and soil suction: key factors in slope stability assessment. They are applied to the PRIME resistivity models, using different relationships for each lithological unit present in the landslide, as informed by the 3-D ground model. This allows the time-lapse resistivity models to be used to monitor temporal changes in moisture content and soil suction. The PRIME images reveal complex hydrogeological pathways and subsurface responses to seasonal changes in weather conditions, providing an important step toward identifying precursors to failure, with the long-term aim of predicting the timing of failure at this site.
Huang, W. (2021). Efficient analytical approach for stability analysis of infrastructure slopes. Proceedings of the Institution of Civil Engineers – Geotechnical Engineering, 1-14. DOI: https://doi.org/10.1680/jgeen.21.00106
Abstract: Transportation infrastructure is of vital importance to economic prosperity. Transportation infrastructure (e.g. railway, highway) is usually supported by a large number of cuttings and embankments, which require regular maintenance to ensure serviceability and safety. The funding available for maintenance is usually limited. Hence, the key challenge is to identify the infrastructure slopes that require the most urgent attention. This paper presents an analytical framework that can be efficiently used for slope stability analysis at network scales. The analytical approach enables calculation of the factor of safety according to the traditional approach, the over-design factor following Eurocode 7 and the probability of failure considering uncertainty of parameters. Application of the analytical framework is illustrated with examples. The analytical approach can readily be incorporated into a spreadsheet program as user-defined functions, which are particularly useful for the generic slope stability analysis of long linear transportation infrastructure.
Huang, W., Dijkstra, T., Loveridge, F., Hughes, P., Blake, A. P., Dobbs, M., Gonzalez, Y. T. (2022). Spatial variability of London Clay using CPT and SPT data. 8th International Symposium on Geotechnical Safety and Risk (ISGSR 2022), Newcastle, Australia, 14–16 December 2022. https://doi.org/10.3850/978-981-18-5182-7_00-03-015.xml
Abstract: London Clay has been the subject of intensive investigations, but further research is required to characterize the spatial variability in greater detail. This study focuses on establishing a measure of the spatial variability using the Scale of Fluctuation (SoF), a key input into random field modelling of geotechnical problems. At two sites in Central London, the SoF is calculated using cone penetration tests (CPT) and standard penetration tests (SPT), both driven perpendicular to the lithostratigraphic sequence. The vertical interval (spacing) of CPT data is 0.02 m. The spacing of SPT data is ≥ 1.5 m. The results show that the vertical SoF from CPT is 0.24 – 1.01 m with a mean of 0.48 m; the vertical SoF from SPT is 0.96 – 3.99 m with a mean of 2.26 m. The SoF from SPT is close to the SPT data spacing, therefore the accuracy of SoF from SPT is questionable. The results also suggest that the main drivers for spatial variability are likely attributed to sedimentary cycles acting over thousands of years. The results do not provide sufficient resolution to evidence any seasonal variations.
Huang, W., Loveridge, F., Briggs, K. M., Smethurst, J. A. (2022). Effect of climate change on pore-water pressure regimes for earthwork design. 16th BGA Young Geotechnical Engineers Symposium, Newcastle upon Tyne, UK, 4th – 5th July 2022.
Huang, W., Loveridge, F., & Satyanaga, A. (2022). Translational upper bound limit analysis of shallow landslides accounting for pore pressure effects. Computers and Geotechnics, Volume 148. https://doi.org/10.1016/j.compgeo.2022.104841
Abstract: Many rainfall-induced landslides are reported to be shallow. Therefore, when regional slope stability analysis, or landslide hazard mapping is carried out, simple approaches, such as the infinite slope model, are often used. However, the infinite slope model is known to underestimate the factor of safety due to the absence of boundary effects. More sophisticated methods that account for the boundary effects at the toe and head of the landslide are much more computationally expensive. In this paper upper bound limit analysis (UBLA) is presented with a novel failure mechanism which consists of a translational parallelogram in the middle slope and two log-spiral components at the slope crest and slope toe to capture the boundary effect. The new approach is derived for a full range of pore water pressure conditions and validated by finite element limit analyses. For shallow landslides the translational UBLA is found to outperform the conventional log-spiral UBLA. The results of a large parametric study using the translational UBLA are then used to develop a novel analytical shallow landslide model which retains the simplicity of the traditional infinite slope model, but yet improves accuracy considerably, making this an attractive alternative for routine analysis such as landslide hazard mapping.
Hughes PN, Margrave-Jones S, Huang C, Dobson K, Toll DG, Stirling RA, and Glendinning S (2019). Laboratory Assessment of the Impact of Freeze-Thaw-Cycling on Sandy-Clay Soil. XVII ECSMGE-2019, 1-6 Sept, 2019, Reykjavic, Iceland. European Conference on Soil Mechanics and Geotechnical Engineering, [pdf]
Abstract: Understanding the mechanisms of engineered soil slope degradation is essential for efficient management and maintenance of transport infrastructure networks. In temperate zones such as the United Kingdom recent research has focussed on the impacts of cycles of wetting and drying on hydraulic and mechanical properties though less attention has been given to temperature cycling. This paper investigates the impact of freeze-thaw-cycles (FTCs) on the shear strength, stiffness and soil water retention properties of a UK Glacial Till. X-ray computed tomography (XRCT) scanning was used to identify soil fabric changes linked to changes in soil properties. Scans revealed progressive cracking and potential pore redistribution as the number of FTCs increased. Repeated FTCs led to lower soil suctions, shear strengths and stiffness. After 6 FTCs, the soil had lost: significant suction potential, 32% of its original shear strength and 14% of its original stiffness. The research suggests that in the case of the soil studied, suction reductions were the dominant factor behind FTCs’ influence over soil strength with cracking being a lesser component. Similarities have been identified between the effects of FTCs and repeated wetting and drying.
Loke M, Wilkinson P, and Chambers J, (2019). 3-D resistivity inversion with electrodes displacements. ASEG Extended Abstracts, 25th International Conference and Exhibition – Interpreting the Past, Discovering the Future, epub: 12 Feb 2019. doi.org/10.1071/ASEG2016ab125
Abstract: 3-D resistivity monitoring surveys are used to detect temporal changes in the subsurface using the measurements repeated over the same site. The positions of the electrodes are measured at the start of the survey program and perhaps at occasional intervals. In areas with unstable ground, the positions of the electrodes can be displaced by ground movements. If this occurs at times when the positions of the electrodes are not measured, they have to be estimated from the resistivity data. The smoothness-constrained least-squares optimisation method can be modified to include the electrodes positions as additional unknown parameters. 3-D resistivity surveys present a special challenge due to the greater computational requirements for the forward modelling routine and the possible movements of the electrodes in three directions. To reduce the calculation time, a fast adjoint-equation method is used to calculate the Jacobian matrices required by the least-squares method. It is several orders of magnitude faster than the simpler perturbation method previously used for 2-D problems. In areas with large near-surface resistivity contrasts, the inversion routine sometimes cannot accurately distinguish between electrodes displacements and subsurface resistivity variations. To overcome this problem, the model for the initial time-lapse data set (with accurately known electrodes positions) is used as the starting model for the inversion of the later-time data set. This greatly improves the accuracy of the estimated electrode positions compared to the use of a homogeneous half-space starting model.
Liu G, Toll DG, Kong L, Asquith JD (2020). Matric Suction and Volume Characteristics of Compacted Clay Soil under Drying and Wetting Cycles. Geotechnical Testing Journal Vol 43, no. 2, March 2020: 464-479. epub: 22 Apr 2019. doi.org/10.1520/GTJ20170310 [alternatively, please follow this link]
Abstract: The influence of drying and wetting cycles on matric suction and volume characteristics of a compacted low plasticity clay soil was studied experimentally. An apparatus was developed where soil specimens were placed in direct contact with a high suction tensiometer, then repeated drying and wetting cycles were applied; drying by means of evaporation and wetting using the application of water droplets. The matric suction, vertical and radial displacement, and mass change of the specimens were all monitored continuously during the cycles. The equipment is the first to provide natural drying, unconstrained shrinkage or swelling with continuous measurements of volume, suction and water content in a way that could readily be used in engineering practice. The results indicated that drying-wetting cycles resulted in accumulated irreversible shrinkage. However, the amount of shrinkage decayed very significantly as the number of cycles increased, and the behaviour became almost repeatable after the third cycle. It was also observed that the positions of soil water retention curves (SWRC) under wetting-drying cycles shift downwards with the increasing number of cycles; the larger the number of cycles, the smaller the difference between the curves and after 2 or 3 cycles, the difference became steady. The shape of the curves changed very obviously under the first three wetting-drying cycles but less significantly after this.
Maguda Vishwanath, S., Hughes, P.N., Augarde C.E. (2021) Cross-linking of biopolymers for soil earthen construction. Building Research & Information, Vol. 50, Issue 5, p. 502-514. http://dx.doi.org/10.1080/09613218.2021.2001304
Abstract: Biopolymers are promising potential soil stabilizers due to their ease of application and stabilization efficacy. Biopolymers are biologically occurring polymers that form hydrogels when added to soil in the presence of water. Hydrogels are three-dimensional polymer networks formed through the interaction of polymer chains with soil particles and pore water. The chemical properties of the biopolymer and external factors (like temperature) affect the physical characteristics of the hydrogels formed. Cross-linking of biopolymer chains with another monomer or biopolymer enables the development of hydrogels with enhanced physical integrity and mechanical properties. Recent studies have shown that the biopolymers, guar and xanthan gums, improve the mechanical and durability properties of soil. As a galactomannan, guar gum naturally forms cross links with xanthan gum, and the study presented here evaluates the impact of this cross-linking on plasticity, shrinkage, strength and durability. Cross-linked specimens with higher guar gum have higher plasticity indices and linear shrinkage; however, when the amount of xanthan gum is increased, these values reduce. Strength tests suggest that cross-linking addresses some of the shortcomings of each biopolymer and improves the overall mechanical behaviour of the soil. The durability performance of cross-linked specimens was found to be comparable with specimens stabilized with individual biopolymers.
McConnell E, Holmes J, Stirling R, Davie CT, Glendinning S. (2022). Multiscale approach to the investigation of desiccation cracking and its influence on the hydraulic regime in high plasticity clay. 16th BGA Young Geotechnical Engineers Symposium, Newcastle upon Tyne, UK, 4th – 5th July 2022. https://doi.org/10.57711/kz8q-q554
Abstract: Slope instability within clay embankments, caused by preferential infiltration through desiccation cracks, is set to increase under climate change intensification of weather extremes. Infiltration within a desiccated slope depends on crack pattern, which evolves temporally with climate. Therefore, an understanding of crack formation processes, and how this influences slope hydrology, is required to identify the impact of climate change on desiccated slopes. This study uses a multiscale approach to link findings from laboratory investigations, into the role of construction practices on crack formation, with decisions and observations made during construction and long-term hydrologic monitoring of a large-scale lysimeter slope. Preliminary laboratory results indicate a thicker, sand-based topsoil reduces the evaporation, and therefore cracking potential, of the Ampthill Clay. The lysimeter slope is highly sensitive to changes in moisture content in the upper 100 mm where cracks have formed therefore, applying topsoil could dampen this response. This highlights a multi-scale approach’s effectiveness in understanding the contribution of individual parameters to crack formation and translating the results to field-scale observations.
McConnell E, Holmes J, Stirling R, Davie CT, Glendinning S. (2022). Hydrological monitoring of an outdoor, large-scale desiccation crack experiment. 11th International Symposium on Field Monitoring in Geomechanics, London, UK, 4th – 8th September 2022. https://doi.org/10.57711/qv4x-f230
Abstract: Climate-driven deterioration from desiccation cracking, together with increased climate variability, is a growing threat to the stability, and therefore management of infrastructure embankments. Desiccation cracking at multiple scales increases assets’ vulnerability to failure by imposing irrecoverable spatial and transient changes in soil hydromechanical properties. Current research into the relationship between climate change, slope deterioration and soil water retention capacity within a cracked slope, at a scale comparable to field embankments, is limited. Understanding this relationship is crucial in order to formulate a deterioration and remediation framework for infrastructure assets’ experiencing desiccation cracking. Preliminary results are presented in this paper from a large-scale (4500 x 2000 x 1200 mm), heavily instrumented slope within an outdoor lysimeter located at the UKCRIC National Green Infrastructure Facility, Newcastle University, UK. The lysimeter is an opportunity to monitor the hydrological regime and water retention capacity of a cracked slope in situ, under natural and simulated weather events.
Mendes, J, Gallipoli, D, Tarantino, A and Toll, D (2019). On the development of an ultra-high-capacity tensiometer capable of measuring water tensions to 7 MPa. Géotechnique, Vol 69, Issue 6, June 2019, pp. 560-564. epub: 13 May, 2019. doi.org/10.1680/jgeot.18.T.008
Abstract: Tensiometers are increasingly used in geotechnical engineering to monitor pore-water tension in the field and to study the hydro-mechanical behaviour of unsaturated soils in the laboratory. Early tensiometers exhibited a relatively small measuring range, typically limited to a tension of 0·1 MPa, due to the breakdown of water tension inside the sensing unit at absolute negative pressures. This limitation was subsequently overcome by the design of high-capacity tensiometers (HCTs), which enabled the measurement of considerably larger pore-water tensions. According to the literature, the highest value of water tension ever recorded by an HCT is 2·6 MPa. In the present work, this value is almost tripled by designing a novel ultra-high-capacity tensiometer (UHCT) capable of recording water tensions up to 7·3 MPa. This is achieved by replacing the traditional ceramic interface with a nanoporous glass (typically employed by physicists for the study of confined liquids), which has never been used before in the manufacture of tensiometers. The maximum attainable tension has been determined using tests where the UHCT measurement was progressively increased by vaporising water from the glass interface until the occurrence of tension breakdown (often referred to as ‘heterogeneous cavitation’ or ‘tensiometer cavitation’). The increased measuring range and the potentially larger measuring stability of the proposed UHCT will contribute to enhance laboratory testing of soils at high suctions and long-term monitoring of earth structures.
Mendes, J, Gallipoli, D, Toll, DG, and Tarantino, A, (2018). First Saturation and Resaturation of High Capacity Tensiometers with 1.5 MPa High Air Entry Value (HAEV) Ceramic Filters. Second Pan-American Conference on Unsaturated Soils. [pdf]
Abstract: High capacity tensiometers, or HCTs, are sensors that can measure negative pore water pressures (soil suctions) between −1.5 and −2 MPa. To achieve such measured values, HCTs first need to be fully saturated by water. For the first saturation of an initially dry HCT, the most common procedure involves application of vacuum followed by forced flooding by pressurised water. Instead, for the resaturation of a HCT that has cavitated (and is therefore still water flooded), only application of water pressure is necessary. Typically, the procedures for the first saturation and resaturation of HCTs can last days or weeks, which hinders adoption of these devices by the geotechnical industry. In this paper, faster procedures are presented for both first saturation and resaturation of HCTs built with 1.5 MPa air entry value filters. The duration of the first saturation can be reduced to less than 24 h if high vacuum is first applied to the ceramic filter followed by water pressurisation at about twice the air entry value of the filter. Even more, resaturation of a cavitated HCT can be achieved in less than 10 min by simple water pressurisation of the ceramic filter. This is however true only if the HCT is not left to dry out to the atmosphere completely and is submerged in water just after cavitation.
Morsy, A., Helm, P.R., El-Hamalawi, A., Smith, A., Hughes, P.N., Stirling, R.A., Dixon, N. & Glendinning, S. (2023). Development of a Multi-Phase Numerical Modeling Approach for Hydromechanical Behavior of Clay Embankments Subject to Weather-Driven Deterioration. ASCE Journal of Geotechnical and Geoenvironmental Engineering, Vol. 149, Issue 8. https://doi.org/10.1061/JGGEFK.GTENG-11213
Abstract: Clay embankments used for road, rail, and flood defense infrastructure experience a suite of weather-driven deterioration processes that lead to a progressive loss of hydromechanical performance: micro-scale deformation (e.g., aggregation and desiccation), changes in soil-water retention, loss of strength, and macro-scale deformation. The objective of this study was to develop a numerical modeling approach to simulate the construction and long-term, weather-driven hydromechanical behavior of clay embankments. Subroutines within a numerical modeling package were developed to capture deterioration processes: (1) strength reduction due to wet-dry cycles; (2) bimodality of the near-surface hydraulic behavior; (3) soil-water and soil-gas retentivity functions considering void ratio dependency; and (4) hydraulic and gas conductivity functions considering void ratio dependency. Uniquely, the modeling approach was comprehensively validated using laboratory tests and nine years of field measurements from a full-scale embankment. The modeling approach captured the variation of near-surface soil moisture and matric suction over the monitored period in response to weather cycles. Further, the developed model approach could successfully simulate weather-driven deterioration processes in clay embankments. The model predictions manifested the ability of the modeling approach in capturing deterioration features such as irrecoverable increases in void ratio and hydraulic permeability near surface. The developed and validated numerical modeling approach enables forecasting the long-term performance of clay embankments under a range of projected climate conditions.
Muddle, D.M. and Briggs, K.M., 2019. Macropore structure and permeability of clay fill samples from a historic clay fill earthwork. Transportation Geotechnics, 19, pp.96-109. https://doi.org/10.1016/j.trgeo.2019.02.003
Abstract: Near surface macropores and macro features (e.g. cracks and fissures) provide pathways for rapid water infiltration into the core of clay fill earthworks. However it is more difficult to measure the size and distribution of macropores located below the weathered soil surface (>1.5 m depth) and hence assess their influence on water flow through the clay fill core of an earthwork. This paper explores the influence of macropores on the rate of water flow within the core of a historic railway earthwork. Samples were excavated from the core (1.5 m–6.5 m depth) of a clay fill railway embankment and subjected to laboratory saturated hydraulic conductivity testing. The samples were scanned using X -ray computed tomography (XCT) before and after laboratory testing. XCT was used to measure the size and distribution of macropores (>63 × 10−6 m) within the samples and compare with the saturated hydraulic conductivity measurements. The results showed that the distribution of macropores and the saturated hydraulic conductivity of the samples from the embankment core was not dependant on the depth of excavation. The total macroporosity of the samples was very small relative to the total porosity (less than 10%). The saturated hydraulic conductivity of the samples was more closely related to the connectivity of the macropores (mean length) than to the total porosity or the total macroporosity. The macropores were variably distributed within the core of the clay fill embankment, they did not show a clear relationship with depth and they were connected over relatively short lengths (the mean macropore length was not greater than 1.6 × 10−3 m). Therefore water flow through the core of the embankment is likely to be through the clay fill matrix, rather than through the connected macropore pathways which allow rapid water infiltration at the near soil surface (<1.5 m depth).
Mugarza E, Glendinning S, Stirling R, Davie CT (2022). Climate Change Impact on Earthworks Slope Stability: A Study of Drainage Design. 16th BGA Young Geotechnical Engineers Symposium, Newcastle upon Tyne, UK, 4th – 5th July 2022.
Postill, H, Helm, PR, Dixon, N, El-Hamalawi, A, Glendinning, S and Take, WA (2021). Strength parameter selection framework for evaluating the design life of clay cut slopes. Proceedings of the Institution of Civil Engineers – Geotechnical Engineering. Published online ahead of print. DOI: https://doi.org/10.1680/jgeen.21.00125
Abstract: Design of engineered earthworks is predominately conducted through limit equilibrium analysis requiring strain independent strength criteria. Previous studies for deep-seated first-time failures within over-consolidated clay cut slopes have proposed the use of fully softened strength parameters for design. A study investigating shallow first-time failures in clay cut slopes due to seasonal stress cycles has been undertaken using a validated numerical model capable of capturing seasonal ratcheting and progressive failure. It is shown that fully softened strength criteria are inappropriate for the assessment of shallow first-time failures due to seasonal ratcheting and that slopes at angles between the material’s fully softened and residual friction angle may be at risk of failure in the future due to this behaviour. However, adopting residual strength parameters will likely result in overly conservative solutions considering the required design life of geotechnical assets. It is shown that the strain-softening behaviour of clay defines the rate of strength deterioration and the operational life of engineered slopes. While general guidelines for analysis considering shallow first-time failures in clay cut slopes are made, detailed understanding of a material’s strain-softening behaviour, the magnitude and rate of strength reduction with strains, is needed to establish strength criteria for limit equilibrium analysis.
Postill H, Dixon N, Fowmes G, El–Hamalawi A, and Take AW, (2019). Modelling Seasonal Ratcheting and Progressive Failure in Clay Slopes: A Validation. Canadian Geotechnical Journal, epub: 16 October 2019. doi.org/10.1139/cgj-2018-0837 [alternatively, please follow this link]
Abstract: Seasonal wetting and drying stress cycles can lead to long-term deterioration of
high-plasticity clay slopes through the accumulation of outward and downward deformations leading to plastic strain accumulation, progressive failure and first-time failures due to seasonal ratcheting. Using recent advances in hydro-mechanical coupling for the numerical modelling of unsaturated soil behaviour and development of nonlocal strain-softening regulatory models to reduce mesh dependency of localisation problems, the mechanism of seasonal ratcheting has been replicated within a numerical model. Hydrogeological and mechanical behaviours of the numerical model have been compared and validated against physical measurements of seasonal ratcheting from centrifuge experimentation. Following validation, the mechanism of seasonal ratcheting was explored in a parametric study investigating the role of stiffness and long-term behaviour of repeated stress cycling extrapolated to failure. Material stiffness has a controlling influence on the rate of strength deterioration for these slopes; the stiffer the material, the smaller the seasonal movement and therefore the more gradual the accumulation of irrecoverable strains and material softening. The validation presented provides confidence that the numerical modelling approach developed can capture near-surface behaviour of high-plasticity overconsolidated clay slopes subject to cyclic wetting and drying. The approach provides a tool to further investigate the effects of weather driven stress cycles and the implication of climate change on high-plasticity clay infrastructure slopes.
Postill, H (2019). Cooling Prize Paper: Clay cut slope deterioration, climate change and maintenance. Ground Engineering, 13 June. [link]
Postill, H, Helm, PR, Dixon, N, Glendinning, S, Smethurst, JA, Rouainia, M, Briggs, KM, El-Hamalawi, A and Blake, AP (2021). Forecasting the long-term deterioration of a cut slope in high-plasticity clay using a numerical model. Engineering Geology, Volume 280, 105912, DOI: https://doi.org/10.1016/j.enggeo.2020.105912
Abstract: This paper details development of a numerical modelling approach that has been employed to forecast the long-term performance of a cut slope formed in high plasticity clay. It links hydrological and mechanical behaviour in a coupled saturated and unsaturated model. This is used to investigate the influence of combined dissipation of excavation-generated excess pore water pressures and seasonal weather-driven near-surface cyclic pore water pressures. Deterioration of slope performance is defined in terms of both slope deformations (i.e. service) and factor of safety against shear failure (i.e. safety). Uniquely, the modelling approach has been validated using 16 years of measured pore water pressure data from multiple locations in a London Clay cut slope. Slope deterioration was shown to be a function of both construction-induced pore water pressure dissipation and seasonal weather-driven pore water pressure cycles. These lead to both transient and permanent changes in factor of safety due to effective stress variation and mobilisation of post-peak strength reduction over time, respectively, ultimately causing shallow first-time progressive failure. It is demonstrated that this long-term (90 year) deterioration in slope performance is governed by the hydrological processes in the weathered near surface soil zone that forms following slope excavation.
Rouainia M, Helm PR, Davies O and Glendinning S (2020). Deterioration of an infrastructure cutting subjected to climate change. Acta Geotechnica, epub 19 May 2020. doi.org/10.1007/s11440-020-00965-1 [alternatively, please follow this link]
Abstract: Observations show that many soils in linear geotechnical infrastructure including embankments and cuttings undergo seasonal volume changes, and different studies confirm that this is due to cycles in climatic and hydrological conditions. These cycles can give rise to progressive failure of the soil mass, which in turn may lead to deterioration of performance
and ultimately slope failure. It is expected that the magnitude of the seasonal cycles of pore pressure will be increased by more extreme and more frequent events of wet and dry periods predicted by future climate scenarios. In this paper, numerical modelling has been undertaken to simulate a continuous time series pore water pressure within a representative cutting in London Clay. The approach uses synthetic control and future climate scenarios from a weather generator to investigate the potential impacts of climate change on cutting stability. Surface pore water pressures are obtained by a hydrological model, which are then applied to a coupled fluid-mechanical model. These models are able to capture the significant soil–vegetation–atmospheric interaction processes allowing the induced unsaturated hydro-mechanical response to be investigated. The chosen hydraulic conductivity variables in the model are shown to affect the total magnitude of pore pressure fluctuation and hence the rate of progressive failure. The results demonstrate for the first time that higher total magnitude of annual variation in pore pressures caused by future climate scenarios can have a significant effect on deformations in cuttings. This in turn leads to increased rates of deterioration and reduces time to failure.
Smethurst, J.A., Sellaiya, A., Blake, A.P. and Powrie, W., (2022). A Long-Term Record of Water Content and Pore Water Pressure in a Vegetated Clay Highway Cut Slope. In Advances in Transportation Geotechnics IV (pp. 767-779). Springer, Cham. https://doi.org/10.1007/978-3-030-77238-3_58
Abstract The major highway network in the UK was developed from the 1960s, and the earthworks are generally well engineered. However, as many of the earthworks get older, slope failures are becoming more common, with some posing a threat to the safety of transport operations. Field measurements of soil water content and pore water pressure changes within the surface zone of a highway cut slope in London Clay at Newbury, Berkshire, UK, have been carried out continuously since 2003. This paper describes and gives examples of the long-term field measurements from the site at Newbury and details a number of significant findings from the observations from the site. The paper explains how these have been used to calibrate appropriate models of seasonal cycles of pore water pressure and slope deterioration.
Sophocleous, M., Atkinson, J.K., Smethurst, J.A., Espindola-Garcia, G. and Ingenito, A., 2020. The use of novel thick-film sensors in the estimation of soil structural changes through the correlation of soil electrical conductivity and soil water content. Sensors and Actuators A: Physical, 301, p.111773.
Abstract: Novel, low-cost, screen-printed (thick-film) conductivity sensors have been incorporated into laboratory-based soil columns together with water-content sensors, so that changes in the soil structure could be monitored through correlation of changes in soil conductivity and water content during cyclic wetting and drying of the soil. Significant differences were found in the relationship between the electrical conductivity and water content (CWC) characteristics for the different soil types tested. It was also found that cyclic wetting and draining of the soils, such as would occur due to natural climate effects, produces changes in the CWC characteristics that are indicative of soil structural change.
Stirling RA, Toll DG, Glendinning S, Helm PR, Yildiz A, Hughes PN, and Asquith JD (2020). Weather-driven deterioration processes affecting the performance of embankment slopes. Géotechnique 2020, epub ahead of print: 23 April 2020. doi.org/10.1680/jgeot.19.SiP.038 [alternatively, please follow this link]
Abstract: Deterioration of earthworks and the resultant implications for serviceability and increased occurrence of failures have a significant negative impact on transport networks both in the UK and internationally. There is evidence in the field that deterioration processes are occurring over the life of an asset, comprising cracking and loss of suction. These are weather-driven processes that occur in the absence of increased mechanical loads and can lead to failure many years after construction. To demonstrate the progressive loss in mechanical performance of clay fill due to a purely environmentally driven deterioration process, a programme of unsaturated triaxial testing was carried out. A new mechanism of soil deterioration driven by cyclic wetting and drying is proposed, based on an extensive laboratory and field experimental programme. The underlying cause for this is the micro-structural changes to the soil fabric leading to loss of suction generation capacity. In addition, cracking leads to changes in hydraulic conductivity and the movement of water into and out of the soil. The implications for slope stability assessment include the need for changeability of soil parameters and of the ground model, with changes occurring both seasonally and gradually over time.
Svalova, A, Helm, P, Prangle, D, Rouainia, M, Glendinning, S, and Wilkinson, DJ (2021). Emulating computer experiments of transport infrastructure slope stability using Gaussian processes and Bayesian inference. Data-Centric Engineering, Volume 2, E12, DOI: https://doi.org/10.1017/dce.2021.14
Abstract: We propose using fully Bayesian Gaussian process emulation (GPE) as a surrogate for expensive computer experiments of transport infrastructure cut slopes in high-plasticity clay soils that are associated with an increased risk of failure. Our deterioration experiments simulate the dissipation of excess pore water pressure and seasonal pore water pressure cycles to determine slope failure time. It is impractical to perform the number of computer simulations that would be sufficient to make slope stability predictions over a meaningful range of geometries and strength parameters. Therefore, a GPE is used as an interpolator over a set of optimally spaced simulator runs modeling the time to slope failure as a function of geometry, strength, and permeability. Bayesian inference and Markov chain Monte Carlo simulation are used to obtain posterior estimates of the GPE parameters. For the experiments that do not reach failure within model time of 184 years, the time to failure is stochastically imputed by the Bayesian model. The trained GPE has the potential to inform infrastructure slope design, management, and maintenance. The reduction in computational cost compared with the original simulator makes it a highly attractive tool which can be applied to the different spatio-temporal scales of transport networks.
Svalova, A., Helm, P., Prangle, D., Rouainia, M., Glendinning, S., Wilkinson, D.J. (2022) Bayesian emulation of computer experiments of infrastructure slope stability models. 8th International Symposium for Geotechnical Safety & Risk (ISGSR 2022), Newcastle, Australia, 14th – 16th December. https://doi.org/10.3850/978-981-18-5182-7_00-07-011.xml
Abstract: We performed a fully-Bayesian Gaussian process emulation and sensitivity analysis of a numerical model that simulates transport cutting slope deterioration. In the southern UK, a significant proportion of transport infrastructure is built in overconsolidated high-plasticity clay that is prone to deterioration due to seasonal wetting-drying cycles and weather extremes (Stirling 2021; Postill et al. 2021). Geotechnical modelling software (FLAC) was used to simulate the dissipation of excess pore water pressure and seasonal pore water pressure cycles in cuttings (Rouainia et al. 2020). However, due to their high computational expense, it was impractical to perform the number of computer simulations that would be sufficient to understand deterioration behaviour over a range of cutting geometries and soil strength parameters. To address this, we used Gaussian processes and Bayesian inference to emulate the relation between deterioration factors and slope properties (Bastos and O’Hagan 2009). These factors include time to failure (Svalova et al. 2021), failure area, and factor of safety. For our training data, we used a Latin hypercube design to create a computer experiment of 76 numerical models whereby we varied slope height, angle, peak cohesion, peak friction, and permeability. Some of the runs did not reach ultimate limit state failure, resulting in censored times to failure and failure areas. We used Markov chain Monte Carlo sampling to obtain posterior distributions of the emulator parameters, as well as the censored times to failure (Brooks et al. 2010; Kyzyurova 2017). Our emulator could be used to inform slope design, management, and maintenance on different spatio-temporal scales of transport networks.
Toll, D.G. (2020). Stress Components in Unsaturated Soils. Geotechnical Engineering, Vol. 51 No. 3, pp. 19-24. [link]
Toll DG, Bertolini I, and Asquith JD (2019). The effect of compaction conditions on the soil water retention behaviour of a compacted glacial till. XVII ECSMGE-2019, 1-6 Sept, 2019, Reykjavic, Iceland. (European Conference on Soil Mechanics and Geotechnical Engineering). [pdf]
Abstract: An instrumented embankment has been established at Nafferton farm in North East England to investigate the response of an embankment to changing climatic conditions. The embankment was constructed using Durham Lower Glacial Till as the fill material. Soil water retention curves for the embankment soil have been measured in the laboratory using novel high suction tensiometer based equipment that can continuously measure water content, suction and volume change. A suite of soil water retention curves have been measured with a range of techniques, using filter paper, chilled-mirror hygrometer and including the new Durham SWRC apparatus. Good agreement can be seen from the different methods, defining a consistent “primary drying curve”. The paper presents results for specimens compacted wet of optimum water content (gravimetric water content near 25%) and at the water content used for field compaction (gravimetric water content of 20%). Specimens compacted near saturation define a clear primary drying curve. Specimens compacted at the field water content show a flatter response, joining the primary drying curve as suction increases.
Thaman NIJ, Stirling R, Chambers J, Meldrum P, Wilkinson P, Davie CT, Glendinning S, Holmes J. (2022). Developing Novel Geophysical Tools to Investigate Urban Vegetated Soil Moisture Dynamics. 16th BGA Young Geotechnical Engineers Symposium, Newcastle upon Tyne, UK, 4th – 5th July 2022. https://doi.org/10.5194/egusphere-egu22-7386
Summary: Vegetation is an important tool for managing urban surface water and shallow geotechnical assets. However, root water uptake driven changes in slope hydrology (soil water content, matric suction, and hydraulic conductivity) are poorly understood in heterogeneous soils and under extreme climatic conditions. Slope stability is affected by intrinsic factors, including geometry, soil properties, groundwater and vegetation driven matric suction. Field evidence indicates that engineered slopes are susceptible to hydrometeorological slope instability mechanisms and that these pose a potential failure hazard to asset operation and public safety. The UK hosts 15,800 km of railway network and 7100 km of strategic road network, accounting for 49,000 slopes. This is a significant portfolio of slopes that must be managed and maintained at considerable expense. To better understand the influence of vegetation on soil water dynamics in geotechnical infrastructure, Electrical Resistivity Tomography (ERT) is being used. ERT is a non-invasive tool for measuring and imaging subsurface soil moisture dynamics volumetrically. ERT can be used to quantitatively establish how the presence of roots influences transient soil moisture content and suction to assess the effectiveness of vegetation in managing slope hydrology and excess surface water issues in the built environment. This research aims to use 4-D ERT to determine the impact of vegetation on the hydrological behaviour of a high plasticity clay derived sub-soil used in the construction of infrastructure slopes in the southern half of the UK. Laboratory-scale experiments are underway at the UK National Green Infrastructure Facility, Newcastle, using a controlled environment chamber. A suite of soil columns is planted with vegetation, False Oat Grass (Arrhenatherum elatius) and Common Bent (Agrostis capillaris) and feature a 3D ERT electrode array and point sensors for measurement of volumetric water content, matric suction, and electrical conductivity throughout the profile. Through frequent imaging of soil-water-plant interactions and correlation with destructive root architecture imaging, this research aims to highlight how these relationships change over time and respond to extreme weather conditions (drought/inundation) to better predict, manage, and mitigate the occurrence of slope failure. Furthermore, the work aims to improve understanding of vegetation-driven soil moisture movement in the near-surface to better assess seasonal and longer-term slope stability to inform asset management strategies.
Wang, J., Hughes, P.N. and Augarde, C.E., (2022). Effects of fibre additions on the tensile strength and crack behaviour of unsaturated clay. Proceedings of the Institution of Civil Engineers-Ground Improvement, pp.1-53. https://doi.org/10.1680/jgrim.21.00006
Abstract: Desiccation cracking in clay soils is a combined mechanical and hydraulic problem and such soils can be improved by various methods including reinforcement with fibres. The relationships between tensile strength, cracking resistance and water-retention properties of fibre-reinforced fine-grained soils lack coverage in the literature to date. In this study, these three properties are evaluated and connected by way of a series of tensile strength and desiccation cracking tests on fibre-reinforced London clay. The results confirm that increased fibre addition delays the occurrence of peak stress and changes failure behaviour from brittle to ductile. The tensile strength increment gets higher as water content decreases, and reaches a maximum value of 460 kPa when the water content is 12%. The crack intensity factor reduces from 7.20% to 0.89% when 12 mm long fibre is used at a ratio of 0.9%. Fibre reinforcement also changes the crack development pattern by reducing the size of large cracks and increasing the proportion of small individual cracks. However, the presence of fibres was not observed to change the water-retention properties of the soil, indicating that the tensile improvement comes from the pull-out resistance of the fibres rather than suction changes.
White, A, Wilkinson, P, Chambers, J, Boyd, J, Wookey, J, Kendall, J. (2021). Geophysical mapping of badger tunnels in levees. AGU Fall Meeting 2021, New Orleans, LA, 13-17 December 2021. [link]
Summary: Rivers provide freshwater, food, and transport routes but can also cause floods. Flood defences are often long piles of earth and rock, forming embankments or levees. In the UK over 38,000 km of flood defences have been built. Failure of these structures during flood events could cause disruption, property damage and even loss of life. It is therefore essential that levee failure is minimised. These manmade structures make ideal homes for many burrowing animals as they provide sloping ground raised above the surrounding water table. Over several years, animals such the European badger (Meles meles) can build extensive burrow networks through these structures, dramatically compromising their integrity. During flood events the network of tunnels can provide preferential flow paths for flood water, increasing the risk of seepage and piping failures. Piping failure is one of the main causes of levee failure and are commonly associated with animal burrows. European Badgers are a protected species in the UK, so badger setts cannot be disturbed without a license making remediation challenging and expensive. Geophysical methods can provide non-intrusive information about the subsurface so are particularly well suited to imaging tunnel networks. Only sites where badger activity was compromising structural integrity would remediation be needed. Ground Penetrating Radar (GPR) is commonly used to detect cavities, but penetration depth can be limited in clay rich and/or saline environments, often associated with levees. Electrical Resistivity Topography (ERT) is sensitive to voids due to their high resistivity contrast with the surrounding ground and may complement GPR. Unlike GPR, ERT is effective in electrically conductive environments. GPR and ERT have been used to investigate two badger setts located next to levees in the Humber region, United Kingdom. Co-located surveys were undertaken with the aim to image and map the extent of the burrow networks. Each method was interpreted independently to identify potential tunnel networks, before being combined to create a single ground model of each site. The results validate ERT as a suitable methodology for cavity detection in levees. The results will inform remediation plans for each site, allowing further ground truthing of the geophysical results.
Whiteley, J. S., Watlet, A., Kendall, J. M. & Chambers, J. E. (2021) The role of geophysical imaging in local landslide early warning systems. Natural Hazards and Earth Systems Science, Vol. 21, p. 3863–3871. https://doi.org/10.5194/nhess-21-3863-2021
Abstract: We summarise the contribution of geophysical imaging to local landslide early warning systems (LoLEWS), highlighting how the design and monitoring components of LoLEWS benefit from the enhanced spatial and temporal resolutions of time-lapse geophysical imaging. In addition, we discuss how with appropriate laboratory-based petrophysical transforms, geophysical data can be crucial for future slope failure forecasting and modelling, linking other methods of remote sensing and intrusive monitoring across different scales. We conclude that in light of ever-increasing spatiotemporal resolutions of data acquisition, geophysical monitoring should be a more widely considered technology in the toolbox of methods available to stakeholders operating LoLEWS.
Whiteley, J.S., Watlet, A., Uhlemann, S., Wilkinson, P., Boyd, J.P., Jordan, C., Kendall, J.M. and Chambers, J.E., 2021. Rapid characterisation of landslide heterogeneity using unsupervised classification of electrical resistivity and seismic refraction surveys. Engineering Geology, 290, p.106189. https://doi.org/10.1016/j.enggeo.2021.106189
Abstract: The characterisation of the subsurface of a landslide is a critical step in developing ground models that inform planned mitigation measures, remediation works or future early-warning of instability. When a landslide failure may be imminent, the time pressures on producing such models may be great. Geoelectrical and seismic geophysical surveys are able to rapidly acquire volumetric data across large areas of the subsurface at the slope-scale. However, analysis of the individual model derived from each survey is typically undertaken in isolation, and a robust, accurate interpretation is highly dependent on the experience and skills of the operator. We demonstrate a machine learning process for constructing a rapid reconnaissance ground model, by integrating several sources of geophysical data in to a single ground model in a rapid and objective manner. Firstly, we use topographic data acquired by a UAV survey to co-locate three geophysical surveys of the Hollin Hill Landslide Observatory in the UK. The data are inverted using a joint 2D mesh, resulting in a set of co-located models of resistivity, P-wave velocity and S-wave velocity. Secondly, we analyse the relationships and trends present between the variables for each point in the mesh (resistivity, P-wave velocity, S-wave velocity, depth) to identify correlations. Thirdly, we use a Gaussian Mixture Model (GMM), a form of unsupervised machine learning, to classify the geophysical data into cluster groups with similar ranges and trends in measurements. The resulting model created from probabilistically assigning each subsurface point to a cluster group characterises the heterogeneity of landslide materials based on their geophysical properties, identifying the major subsurface discontinuities at the site. Finally, we compare the results of the cluster groups to intrusive borehole data, which show good agreement with the spatial variations in lithology. We demonstrate the applicability of integrated geophysical surveys coupled with simple unsupervised machine learning for producing rapid reconnaissance ground models in time-critical situations with minimal prior knowledge about the subsurface.
Woodman, N., Smethurst, J., Roose, T., Powrie, W., Meijer, G., Knappett, J., Dias, T. (2020). Mathematical and computational modelling of vegetated soil incorporating hydraulically-driven finite strain deformation. Computers and Geotechnics, Volume 127, 2020. https://doi.org/10.1016/j.compgeo.2020.103754
Abstract: In this paper a new model for the hydro-mechanical behaviour of rooted soils is developed. It is a physically-based model that couples finite strain soil deformation with unsaturated water and air flow, while improving on existing cohesion-based approaches to mechanical root reinforcement and empirical soil water-uptake approaches typically used to deal with rooted slopes. The model is used to show that the dynamics of soil-water pressure and soil deformation depend strongly on the physics of the root-water uptake and the elasto-plastic soil mechanics. Root water uptake can cause suctions and corresponding soil shrinkage sufficiently large to necessitate a finite-strain approach. Although this deformation can change the intrinsic permeability, hydraulic conductivity remains dominated by the water content. The model incorporates simultaneous air-flow, but this is shown to be unimportant for soil-water dynamics under the conditions assumed in example simulations. The mechanical action of roots is incorporated via a root stress tensor and a simulation is used to show how root tension is mobilised within a swelling soil. The developed model may be used to simulate both laboratory experiments and full-scale vegetated slopes.
Yu, Z, Eminue, OO, Stirling, S, Davie, C, and Glendinning, S (2021). Desiccation cracking at field scale on a vegetated infrastructure embankment. Géotechnique Letters, Volume 11, Issue 1, pp. 1-21, DOI: https://doi.org/10.1680/jgele.20.00108
Abstract: This paper presents a desiccation crack monitoring campaign conducted on a full-scale, vegetated infrastructure embankment subjected to one-year of seasonally variable weather. The field survey involved direct measurement of naturally developed, annually reoccuring cracks in a heavily instrumented, clay fill embankment (BIONICS, Newcastle University). Transient crack morphology was captured in terms of opening width, length and depth, in addition to meteorological and near-surface soil hydrological conditions. In order to assess any correlation between crack development and weatherdriven changes in near surface soil conditions, the volume of cracks was estimated using an empirically derived equation. This work identified crack behaviour in four stages: initiation, expansion, contraction and closure. These stages and the distribution of cracks on the slope are closely related to prevailing atmospheric conditions, namely wind direction, relative humidity, precipitation and potential evapotranspiration. These ultimately govern the soil hydrological conditions in the near-surface, as manifested in the presented matric potential and volumetric water content data. Linearly discrete cracks are shown to form under such conditions in contrary to the polygonal patterns typically reported under laboratory conditions. Crack length growth terminates prior to full volumetric maturation with crack depth dominating the dynamic response regardless of overall crack size.
Climate change impacts on slope stability
The early days of discussing climate change impact on slope stability were facilitated by a series of meeting for the CLIFFS network. These discussions resulted in a report in 2008 for the (then) Highways Agency (Dijkstra and Dixon 2008; project 5703/CV/HIG) on the effects of climate change impacts on earthwork slopes. This was followed by a more wide-ranging discussion on the challenges and approaches of climate change and slope stability (Dijkstra and Dixon; 2010). A few years later further developments in our approach, informed by projects such as FUTURENET and our development of the narratives underpinning iSMART, were published in Dijkstra et al. (2014) where we set out the theoretical approach to gaining a better understanding of the impacts of climate change on transport infrastructure. A further update on the state of climate change impacts on slopes was published in the book on Slope Safety Preparedness of the Effects of Climate Change edited by Ho et al., (2017; Dijkstra et al., 2017).
Dijkstra, T., Dixon, N., Crosby, C., Frost, M., Gunn, D., Fleming, P., & Wilks, J. (2014). Forecasting infrastructure resilience to climate change. Proceedings of the ICE-Transport, 167(5), 269-280. [pdf]
Dijkstra TA and Dixon N (2010). Climate change and slope stability: Challenges and approaches. Quarterly Journal of Engineering Geology and Hydrogeology, 43(4), 371-385 [pdf]
Dijkstra, T., Jenkins, G., Gunn, D., Dashwood, C., Dankers, R., Dixon, N., Petley, D., Gibson, A., Winter, M. (2017) Chapter 13: Landslides and Climate Change in the United Kingdom. In: Ho, K. Lacasse, S. and Picarelli, L. (eds.) Slope Safety Preparedness of the Effects of Climate Change. CRC Press, Taylor and Francis Group, 437-471p. [link]
Hydraulic conductivity of the near surface
The long-term performance of engineered (e.g. cuttings and embankment) clay slopes is influenced by seasonal cycles of weather, which drive cycles of pore water pressures and hence stress changes. These can lead to progressive failure of the slope. The rate at which water (i.e. rainfall) enters the slope through infiltration is dependent on hydraulic conductivity, often termed permeability, of the near surface. However, there is a dearth of measurements in the literature on this critical material property. Dixon et al. (2019) describe field measurements of saturated hydraulic conductivity conducted by the iSMART project partners at several exemplar embankment and cutting slopes on the UK transport network formed of intermediate and high plasticity clay soils. Dixon et al. (2019) reports 143 individual measurements and considers the factors that influence the spatial and temporal variability obtained. The test methods employed produce near saturated conditions and flow under constant head. For an embankment, hydraulic conductivity was found to vary by five orders of magnitude in the slope near-surface (0–0.3 m depth), decreasing by four orders of magnitude between 0.3 and 1.2 m depth. This extremely high variability is in part due to seasonal temporal changes controlled by soil moisture content, which can account for up to 1.5 orders of magnitude of this variability. Measurements of hydraulic conductivity at a cutting also indicated a four orders of magnitude range of hydraulic conductivity for the near-surface, with strong depth dependence of a two orders of magnitude decrease from 0.2 to 0.6 m depth. The main factor controlling the large range is found to be spatial variability in the soil macro-structure generated by wetting–drying cycle driven desiccation and roots. The measurements of hydraulic conductivity reported were undertaken to inform and provide a benchmark for the hydraulic parameters used in numerical models of groundwater flow. This is an influential parameter in simulations incorporating the combined weather–vegetation–infiltration–soil interaction mechanisms that are required to assess the performance and deterioration of earthwork slopes in a changing climate.
Dixon, N., Crosby, C.J., Stirling, R., Hughes, P.N., Smethurst, J., Briggs, K., Hughes, D., Gunn, D., Hobbs, P., Loveridge, F., Glendinning, S., Dijkstra, T. and Hudson, A. (2019). In-situ measurement of near surface saturated hydraulic conductivity in engineered clay slopes. Quarterly Journal of Engineering Geology and Hydrogeology, Vol. 52, pp. 123–135, DOI 10.1144/qjegh2017-059. [pdf]
A selection of references from the team pre-ACHILLES
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Asquith, J.D., Kong, L., Toll, D.G. and Liu, G., 2019. Matric Suction and Volume Characteristics of Compacted Clay Soil under Drying and Wetting Cycles. Geotechnical Testing Journal, 43(2).
Bergamo, P., Dashwood, B., Uhlemann, S., Swift, R., Chambers, J.E., Gunn, D.A. and Donohue, S., 2016. Time-lapse monitoring of climate effects on earthworks using surface waves. Geophysics, 81(2), pp.EN1-EN15.
Bergamo, P., Donohue, S., Gunn, D.A., Dashwood, B., Uhlemann, S., Chambers, J.E. and Ward, D., 2015, September. Time-lapse monitoring of the slopes of a heritage earthwork by means of near-surface seismic techniques. In Near Surface Geoscience 2015-21st European Meeting of Environmental and Engineering Geophysics.
Briggs, K.M., 2011. Impacts of climate and vegetation on railway embankment hydrology (Doctoral dissertation, University of Southampton).
Briggs, K.M., Smethurst, J.A., Powrie, W. and O’Brien, A.S., 2013. Wet winter pore pressures in railway embankments. Proceedings of the Institution of Civil Engineers-Geotechnical Engineering, 166(5), pp.451-465.
Briggs, K.M., 2010. Charing embankment: climate change impacts on embankment hydrology. Ground Engineering, 43(6), pp.28-31.
Briggs, K.M., Smethurst, J.A., Powrie, W. and O’Brien, A.S., 2016. The influence of tree root water uptake on the long term hydrology of a clay fill railway embankment. Transportation Geotechnics, 9, pp.31-48.
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Briggs, K., Smethurst, J. and Powrie, W., 2014. Modelling the influence of tree removal on embankment slope hydrology. In: Sassa, K., Canuti, P. and Yan, Y.P. (eds.) Landslide Science for a Safer Geoenvironment. Volume 2: Methods of Landslide Studies. Springer International Publishing. (pp. 241-246).
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Chambers, J.E., Meldrum, P., Wilkinson, P.B., Uhlemann, S., Swift, R.T., Inauen, C., Gunn, D., Kuras, O., Whiteley, J. and Kendall, J.M., 2017, December. Towards a geophysical decision-support system for monitoring and managing unstable slopes. In AGU Fall Meeting Abstracts.
Chambers, J., Meldrum, P., Gunn, D., Wilkinson, P., Uhlemann, S., Kuras, O. and Swift, R., 2015. Proactive infrastructure monitoring and evaluation (PRIME): a new electrical resistivity tomography system for remotely monitoring the internal condition of geotechnical infrastructure assets. In 3rd International Workshop on Geoelectrical Monitoring (GELMON). 3rd International Workshop on Geoelectrical Monitoring (GELMON).
Chambers, J.E., Gunn, D.A., Wilkinson, P.B., Meldrum, P.I., Haslam, E., Holyoake, S., Kirkham, M., Kuras, O., Merritt, A. and Wragg, J., 2014. 4D electrical resistivity tomography monitoring of soil moisture dynamics in an operational railway embankment. Near Surface Geophysics, 12(1), pp.61-72.
Chambers, J., Wilkinson, P., Meldrum, P. and Gunn, D., 2011. Forward looking remote monitoring technology for proactive planning. Innovation and Research Focus, 87.
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Dijkstra, T., Dixon, N., Crosby, C., Frost, M., Gunn, D., Fleming, P., & Wilks, J. (2014). Forecasting infrastructure resilience to climate change. Proceedings of the ICE-Transport, 167(5), 269-280.
Dijkstra TA and Dixon N (2010). Climate change and slope stability: Challenges and approaches. Quarterly Journal of Engineering Geology and Hydrogeology, 43(4), 371-385
Dijkstra, T., Jenkins, G., Gunn, D., Dashwood, C., Dankers, R., Dixon, N., Petley, D., Gibson, A., Winter, M. (2017) Chapter 13: Landslides and Climate Change in the United Kingdom. In: Ho, K. Lacasse, S. and Picarelli, L. (eds.) Slope Safety Preparedness of the Effects of Climate Change. CRC Press, Taylor and Francis Group, 437-471p.
Dixon, N., Crosby, C.J., Stirling, R., Hughes, P.N., Smethurst, J., Briggs, K., Hughes, D., Gunn, D., Hobbs, P., Loveridge, F., Glendinning, S., Dijkstra, T. and A. Hudson (2019). In situ measurements of near-surface hydraulic conductivity in engineered clay slopes. Quarterly Journal of Engineering Geology and Hydrogeology, 52(1), 123-135.
Donohue, S., Bergamo, P., Hughes, E., Gunn, D.A., Dashwood, B., Uhlemann, S., Chambers, J.E. and Ward, D., 2015, March. Assessing climate effects on railway earthworks using MASW. In Symposium on the Application of Geophysics to Engineering and Environmental Problems 2015 (pp. 116-120). Society of Exploration Geophysicists and Environment and Engineering Geophysical Society.
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