Experimental Study on Undrained Shear Properties of Saline Soil under Freeze-Thaw Cycles

Shukai Cheng,Yan Han,Jiaqi Wang,Qing Wang,Huazhou Li

doi:10.1155/2021/9987414

Abstract

The freeze-thaw cycle is an important external factor affecting the hydromechanical characteristics of saline soil in cold regions. Due to the presence of water and salt, it has a greater impact on stability. The construction of various projects, such as ditch fills and road subgrades, has mostly used disturbed soils. Therefore, this article takes remolded saline soil in Qian’an, Jilin Province, China, as the research object to evaluate the action of freeze-thaw cycles on the critical state line, effective stress path, pore water pressure-strain relationship, stress-strain relationship, shear strength index, and other mechanical properties via a freeze-thaw cycle test and a consolidated undrained triaxial shear test (CU). The experimental results show that regardless of whether the soil specimen undergoes a freeze-thaw cycle, its stress-strain relationship shows characteristics of strain hardening, while, as the number of freeze-thaw cycles increases, the shear strength gradually decreases. As both the confining pressure and number of freeze-thaw cycles increase, the pore water pressure increases, as does the pore water pressure coefficient in shear failure. Under the action of freeze-thaw cycles, on the p ′ − q plane of the stress space, the effective stress path gradually moves to the lower left side. Both the effective stress path and the pore water pressure characteristics indicate that the degree of consolidation of the soil specimens continuously decreases as the number of freeze-thaw cycles increases. The position of the critical state line gradually lowers, and the critical state stress ratio decreases. The effective stress strength index can more accurately reflect the comprehensive influence of freeze-thaw cycles and confining pressure on the mechanical characteristics of soils than the total stress strength index. Logistic functions can be used to fit and predict the degradation law of the internal friction angle and cohesion.

Highlights

Soil is a three-phase medium, and the effect of water on the soil is very important
As the number of freeze-thaw cycles increased, the undrained shear strength and initial tangent modulus decreased gradually, the pore water pressure corresponding to the same strain gradually increased, eventually slowing down, and the pore water pressure coefficient of the specimen during shear failure gradually increased
The shear strength, initial tangent modulus, and pore water pressure coefficient during failure increased as a function of the freeze–thaw cycles

Summary

Introduction

Soil is a three-phase medium, and the effect of water on the soil is very important. In cold regions, because of the changes in surface temperature, the alternating cycle of freezing and thawing of water in the soil leads to changes in soil deformation and strength characteristics, affecting the stability of various engineering constructions [1]. Studies involving freeze-thaw cycles have evaluated frost heave and thawing deformation, moisture migration, microstructural characteristics, and associated changes in permeability, stress-strain relationship, elastic modulus, and mechanical indicators, as well as a freeze-thaw cycle sensitivity analysis of influencing factors [13,14,15]. In these studies, mechanical properties were the main factors controlling the stability of various types of soil. In the engineering design and stability analysis of seasonally frozen soil, it is typically vital to determine the action of freezethaw cycles on soil mechanical characteristics

Methods

Results

Conclusion