Deformation mechanism and treatment effect of deeply excavated expansive soil slopes with high groundwater level: Case study of MR-SNWTP, China

Abstract

Taking a 4 km long deeply excavated expansive soil canal segment of the South–North Water Transfer Project Middle Route (MR-SNWTP) in China as an example, a comprehensive investigation of the deformation mechanism and effect of treatment work on the slope with high groundwater level was carried out. First, the project background and initial behaviour were introduced. Second, a series of site investigation, including visual inspection, exploration pit, and geological penetrating radar, was employed to identify the deformation characteristics, appearance damage, and groundwater distribution. Third, the environmental factors were analyzed, and the spatio-temporal deformation characteristics were identified. Then the zoned numerical model was built to analyze the slope stability. Finally, the deformation mechanism and effect of treatment work were discussed. The results show that although the slope surface was replaced with a cement-treated weak expansive soil layer, the water vapor exchange between the undisturbed expansive soils and atmosphere is not completely isolated. The perched groundwater is also still replenished by precipitation infiltration. Groundwater, perched groundwater, long-large fissure and dense fissure zone induce the lateral creep deformation of the slope, and result in significant trend changes. The stability of the deformed body is in a critical state. The critical sliding surface is a broken line consisting of a gentle dip angle at the leading edge and a steep dip angle at the trailing edge. The depth of the potential sliding surface varies due to the geological condition and arrangement of anti-slide piles. Drainage wells can discharge deeper groundwater, thus can lower groundwater level and discharge perched groundwater. Supporting and unloading measures should also be taken to improve the slope stability.