Normalized Behavior and Residual Shear Strength of Sand

Abstract

The residual or post-liquefaction shear strength of liquefiable soils and the driving shear stresses are the main factors determining whether a soil mass will experience flow failure and large deformations due to earthquake or non-earthquake loadings. Despite its importance, determining the residual shear strength remains challenging, if not controversial. One method to determine the residual shear strength is by laboratory testing of reconstituted soil samples and to correct for soil sample disturbance using the framework of Critical State Soil Mechanics (CSSM). There are several key requirements before a Critical State (CS) framework can be used for sands: (1) the definition or existence of a CS for sands, (2) the relationship between void ratio e and mean stress p for the Isotropic Consolidation Line (ICL) and the Critical State Line (CSL) for sands, (3) the parallelism of the ICL and CSL, (4) the normalization of the undrained CS or residual shear strength qcs by the effective consolidation or initial stress, and (5) the non-uniqueness of the ICL for sands. This paper presents a new procedure to determine the undrained liquefied or CS shear strength of sands based on the linearity between e and p for both the ICL and CSL. A growing amount of experimental data supports such linearity, particularly at high confining stresses, but has been hitherto ignored because of the "deeply ingrained" use of e vs. log(p) relationship in soil mechanics. The proposed new normalized procedure does not require parallelism between the ICL and CSL. The evaluation is supported by and validated against experimental data.