Effect of strain rate on shear strength and pore pressure behavior of soft soil

Abstract

Soft soils are highly plastic fine grained soils and known for their high compressibility, large water content and low shear strength behavior. The current research is focused on the shear strength behavior of soft soil at different loading rate, stress history & boundary conditions. The soft soil samples are collected from Kanjurmarg, Mumbai; and the slurry consolidation technique is used to prepare the reconstituted specimens of soil at its in-situ water content & density. Limited research has been performed on rate dependent strength behavior of soil, which is restricted to small range of strain rate or non-cohesive/low plasticity soils. An extensive experimental research has been conducted on Kanjurmarg soft soil (CH soil) by performing three series of consolidated undrained triaxial compression tests. These CU triaxial test series explain the following aspects of soft soil: effect of strain rate on shear strength behavior of NC soil, effect of OCR on soft soil for overconsolidation ranging from lightly overconsolidated to heavily overconsolidated stress state, effect of confining pressure on shear response of NC soil, combined effect of strain rate & confining pressure, combined effect of strain rate & OCR. A wide range of strain rate; from 0.005% per min to 5% per min; is used to study the effect of strain rate on shear strength and pore pressure behavior of soft soil. The effect of boundary conditions and stress history has been explored by performing CU triaxial tests on soft soil under confining pressure varying from 100 kPa to 400 kPa and OCR values ranging from 1 to 10 respectively. The combined effect of strain rate and OCR has been studied for strain rate of 0.05% per min & 0.5% per min. The confining pressure influences the strain rate effect on stress-strain & pore pressure evolution of soft soil. The stress history of soft soil also shows its impact on shear behavior of soil at varying strain rate. The effect of loading rate on compressibility response of soft soil is studied by performing 1D consolidation test at different load increment. SEM, AFM, hydrometer & self weight consolidation tests are also performed to evaluate the effect of dispersing agent on behavior of Kanjurmarg soft soil.