Determination of Critical Height of Unsupported Vertical Cuts Using Experimental and Numerical Methods

Stability of unsupported cuts are commonly analyzed numerically as a 2-dimensional problem using commercial geotechnical software such as SLOPE/W. This is also true for the unsupported cuts excavated into unsaturated soils. However, limited experimental studies have been undertaken to validate the numerical approaches in estimating the critical heights of unsupported cuts in unsaturated soils. To bridge this gap, laboratory test was conducted using a large-scale soil tank (W x L x H = 1.5 x 2.2 x 2.4 m) to determine the critical height of an unsupported vertical cut in sand with water table at 0.7 m from the surface. Excavation was simulated by removing 0.1 m height retaining panels until general failure took place. The matric suction profile in sand above the water table was established based on the suction values measured from various depths with high capacity tensiometers (i.e., T5X). The critical height determined in the laboratory test was compared with the one estimated using PLAXIS (3D).