Upper Bound Analysis of the Stability of 3D Slopes in the Saturated Soft Clay Subjected to Seismic Effect

In order to study the three-dimensional stability problem of the saturated soft clay slope under earthquake loads, based on the three-dimensional rotation failure model, the seismic force was introduced into the calculation by the quasi-static method. The work rate of external loads and the internal energy dissipation rate of the saturated soft clay slope were calculated using the upper bound method of limit analysis, and the analytical solution of stability coefficient of saturated soft clay slopes was derived based on the fictitious power principle. By virtue of the exhaust algorithm, the optimal solution of stability coefficient of saturated soft clay slopes was obtained. The influence of the slope angle and the horizontal and vertical seismic forces on the stability coefficient of saturated soft clay slope was analyzed. The results show that the slope angle has a great influence on the stability coefficient, and the relative difference is up to 35.7%. Therefore, the stability coefficient of saturated soft clay slopes can be effectively increased by a proper slope setting. The horizontal and vertical seismic forces also have a significant influence on the stability of saturated soft clay slopes. The relative differences of the stability coefficient under horizontal and vertical seismic forces are as high as 41 and 14.7%, respectively. If they are ignored, the stability coefficient of saturated soft clay slopes will be seriously overestimated. It is suggested that the effects of horizontal and vertical seismic forces must be considered simultaneously in the seismic design of saturated soft clay slopes.

Field Test Research on Red Clay Slope under Atmospheric Action

By embedding water content sensors and pore water pressure sensors inside the red clay slope on-site in Guiyang, Guizhou, shear tests were performed on soil samples at different depths of the slope under different weather. The changes of water content, pore water pressure, and shear strength index of the slope inside the slope under the influence of the atmosphere were tracked and tested, and the failure characteristics and evolution of the red clay slope were analyzed. It is believed that the depth of influence of the atmosphere on red clay slopes is about 0.7 m, rainfall is the most direct climatic factor leading to the instability of red clay slopes, and the evaporation effect is an important prerequisite for the catastrophe of red clay slopes. The cohesion and internal friction angle of the slope soil have a good binary quadratic function relationship with the water content and density. The water content and density can be used to calculate the cohesion and internal friction angle. Failure characteristics of red clay slopes: the overall instability failure is less, mainly surface failure represented by gullies and weathering and spalling, and then gradually evolved into shallow instability failure represented by collapse and slump. The damage evolution law is as follows: splash corrosion and surface corrosion stage⟶ fracture development stage⟶ gully formation stage⟶ gully development through stage⟶ local collapse stage⟶ slope foot collapse stage.

Erosion Control and Growth Promotion of W-OH Material on Red Clay Highway Slopes: A Case Study in South China

Ecological restoration is difficult on the red clay highway slopes in the rainy areas in South China that experience severe soil erosion. By using the hydrophilic polyurethane material W-OH to solidify and protect red clay slopes, the erosion control will be substantially improved. We employed simulated rainfall erosion experiments and pot experiments to evaluate the anti-corrosion and growth promotion performances. We found that, (1) in the initial stage of protection, W-OH had the effect of accelerating slope drainage, solidifying the soil structure, and reducing soil loss, with the sediment reduction benefit reaching 37.4–65.3%. (2) The anti-erosion effect was mainly based on soil solidification. (3) The W-OH was affected by rainfall intensity and the W-OH concentration, and the soil erosion prediction equation was constructed according to the observation. (4) W-OH had a promising water retention performance and can promote the germination and late growth of slope plants to reduce the influence of eluviation. (5) The suitable W-OH solution concentration was 3–5% for slope protection herbs and shrubs, which were commonly used in South China. (6) The reduction in porosity was the fundamental cause of water retention improvement. The ecological restoration of slopes is a comprehensive process. Therefore, both anti-erosion performance and later plant growth are necessary. Our research provides a theoretical and experimental basis for applying the W-OH in the ecological restoration of the red clay slopes in subtropical areas and expanding the scope of the W-OH.

Modelling seasonal ratcheting and progressive failure in clay slopes: a validation

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 hydromechanical coupling for the numerical modelling of unsaturated soil behaviour and development of nonlocal strain-softening regulatory models to reduce mesh dependency of localization 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.