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.
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.
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.
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., 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.
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.
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.
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.
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).
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.
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.
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.
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.
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]
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