Effect of anisotropy on stress-strain and pore pressure response of normally and heavily over consolidated nagpur expansive soil

Abstract

Expansive soil is a residual cohesive soil, mostly present in the arid and semi-arid regions of the world. Stress induced anisotropy is an important aspect to be considered for the analysis and design of several geotechnical structures on expansive soils. Though, its effect is yet to be explored. Hence, the aim of the current study is to evaluate the effect of stress induced anisotropy on the shear behavior of normally and heavily over consolidated Nagpur expansive soil. Nagpur expansive soil is classified as CH (clay with high plasticity) type of soil with high amount of clay content (60%) and high value of differential free swell index (DFSI, 123%). Experimental research has been performed on Nagpur soil by conducting a series of anisotropically (Kc = 0.70, 0.85, 1) consolidated undrained (CU) triaxial compression tests at an over consolidation ratio (OCR) of 1 and 10. Change in void ratio during anisotropic consolidation phase was found to be a function of both, the mean effective stress and deviatoric stress. As Nagpur expansive soil was subjected to pre-shear stress during consolidation phase, its shear behavior showed distinctive response that was different from isotropic condition because of induced stress anisotropy. Normalized undrained shear strength was reduced for anisotropically consolidated specimen in comparison to isotropically consolidated specimen for both the OCR 1 and 10. Excess pore water pressure behavior and the A and βmax parameters were also significantly influenced by the induced stress anisotropy for both the normally and heavily over consolidated states.