Field testing of shear strength of granite residual soils

Abstract

The characteristics of residual soils are very different from those of sedimentary soils. Although the strength characteristics of sedimentary soils have been studied extensively, the shear strength characteristics of granitic residual soils (GRS) subjected to the weathering of parent rocks have rarely been investigated. In this study, the shear strength characteristics of GRS in the Taishan area of southeast China (TSGRS) were studied by field and laboratory tests. The field tests consisted of a cone penetration test (CPT), borehole shear test (BST), self-boring pressuremeter test (SBPT), and seismic dilatometer Marchetti test (SDMT). The shortcomings of laboratory testing are obvious, with potential disturbances arising through the sampling, transportation, and preparation of soil samples. Due to the special structure of GRS samples and the ease of disturbance, the results obtained from laboratory tests were generally lower than those obtained from situ tests. The CPT and scanning electron microscopy (SEM) results indicated significant weathering and crustal hardening in the shallow TSGRS. This resulted in significant differences in the strength and strength parameters of shallow soil obtained by the BST. Based on the SDMT and SBPT results, a comprehensive evaluation method of shear strength for TSGRS was proposed. The SBPT was suitable for evaluating the strength of shallow GRS. The material index (ID) and horizontal stress index (KD) values obtained by the SDMT satisfied the empirical relationship proposed by Marchetti based on the ID index, and were therefore considered suitable for the evaluation of the shear strength of deep GRS.