Determination of critical height and critical distance of unsupported vertical cuts in unsaturated soils

Abstract

This study investigates how the level of groundwater table and foundation stress intensity affect the critical height of unsupported vertical cuts. Stability analyses were performed using SLOPE/W (GeoStudio 2023) for various soil types with a broad range of plasticity indices. Based on the analyses results, critical distances - the distance between the edge of a shallow foundation and the face of an unsupported vertical cut where the critical heights are not influenced by groundwater table level and foundation stress - are proposed for different soil types. To validate the methodology, large-scale laboratory tests were conducted at the geotechnical laboratory of UNB, using a soil tank filled with cohesionless soil to simulate foundation stress near the unsupported vertical cut. For cohesive soils, comparable load test results on unsaturated slopes from the literature were revisited. This study is expected to provide practical guidelines for excavating unsupported vertical cuts near an existing superstructure in unsaturated soils.