A new geotechnical method for natural slope exploration and analysis

Abstract

Geotechnical investigation of natural slopes is challengeable especially when natural slopes having higher gradients and access is difficult. Also, it is even more problematic to find the shear strength parameters spatially to evaluate the stability of slopes as most of the methods available to find the shear strength parameters in the literature are uneconomical or such methods cannot be applied in vegetated slopes. Recently, authors have conducted a series of in situ investigations based on the newly developed lightweight dynamic cone penetrometer to examine its applicability in analyzing the slopes covered with weathering remnants of decomposed granite. Six patterns were identified based on the penetration resistance varies with the depth. Spatial variability analysis conducted on different grid spaces showed that the coefficient of variation of cone resistance varies from 0 to 35 %. Semi-variogram analysis showed that the Spherical Models can be used to evaluate the spatial variability of weathering remnants of decomposed granite. A series of laboratory calibration tests based on the lightweight dynamic cone penetration tests and direct shear tests with pore pressure measurements were conducted at different void ratios and degrees of saturation. Based on the laboratory calibration test results, a method to determine the void ratio, e, from the data of qd was presented. Based on this, two formulas to evaluate the shear strength parameters, apparent cohesion and friction angle, were established with the cone resistance and degree of saturation. Slight modification was proposed in evaluating the apparent cohesion with respect to the different fine content in the soils. As a whole, the proposed method can be successfully applied to individual slopes to determine the profile thickness and to evaluate the shear strength parameters spatially. Based on this, hazard assessment of individual slopes can be made.