Development of a multi-phase numerical modeling approach for hydromechanical behavior of clay embankments subject to weather-driven deterioration

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 increase in void ratio and hydraulic permeability near surface. The developed and validated numerical modeling approach enables forecasting of the long-term performance of clay embankments under a range of projected climate conditions.</p

Evidence for the weather-driven deterioration of ageing transportation earthworks in the UK

Seasonal, weather-driven pore pressure cycles alter and degrade the hydro-mechanical engineering properties of earthworks as they age. The accumulating effects of deterioration over many years can lead to the excessive deformation or failure of earthworks; requiring interventions to ensure their reliable performance. This paper reviews the evidence for the weather-driven deterioration of ageing transportation earthworks, with a focus on clay earthworks in the UK. These include earthworks of various ages (up to ∼200 years old), formed from a range of clay-rich strata and at various stages of deterioration. Evidence is considered for both past behaviour and projected behaviour in response to continued ageing and a changing climate. There is clear evidence that some clay earthworks are influenced by the cumulative effect of seasonal weather cycles over many decades. Simulations show that seasonal slope ratcheting will become an increasingly dominant driver of shallow failures in high-plasticity cut slopes as they age and in response to projected climate change. The evidence can inform performance curves describing the deterioration of individual earthworks in response weather-driven ageing. This can help identify earthworks with the highest likelihood of failure and inform decisions made by earthwork asset managers.</p

Long-term monitoring of long linear geotechnical infrastructure for a deeper understanding of deterioration processes

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. </p