Experiment and analysis of slope failure of debris-flow fans

Failure of debris flow fan is distinct from the common rock and soil slope failure due to the unique geotechnical features of debris flow sediment. However, this type of failure has not been comprehensively and systematically studied in the past. In our recent research, a practical subroutine is developed to interpret the slope stability using a Visual Basic application embedded in Microsoft Excel. The Spencer slicing method with varying physical parameters along the slice depth is used to search for the noncircular critical slip surface from a calculated circular critical slip surface. This is done using spreadsheet-automated constrained optimization. The results are then compared with in situ observed slip surface. The in situ experiment indicated that the water content hardly changed at a depth of 50 cm beneath the surface after a period of concentrated artificial rainfall, but the landslide failed anyway. With the increase in height of the soil layer, the calculated safety factor gradually decreased and an optimized noncircular slip surface with an average height of 2.4 m was obtained satisfying all the constraints and assumptions. However, there was a discrepancy between the calculated slip Surface and the actual sliding surface, despite using parameters adopted from the in situ experiment and laboratory testing. Briefly, the method of slices to perform slope stability analysis for investigating slope failure of debris flow fans was unsuccessful due mainly to inconsistencies between the stability analysis and experimental observation.