Effect of freeze-thaw cycles on uniaxial mechanical properties of cohesive coarse-grained soils

Freeze-thaw cycles are closely related to the slope instability in high-altitude mountain regions. In this study, cohesive coarse-grained soils were collected from a high-altitude slope in the Qinghai–Tibet Plateau to study the effect of cyclic freeze-thaw on their uniaxial mechanical properties. The soil specimens were remolded with three dry densities and three moisture contents. Then, after performing a series of freeze-thaw tests in a closed system without water supply, the soil specimens were subjected to a uniaxial compression test. The results showed that the stress-strain curves of the tested soils mainly performed as strain-softening. The softening feature intensified with the increasing dry density but weakened with an increase in freeze-thaw cycles and moisture content. The uniaxial compressive strength, resilient modulus, residual strength and softening modulus decreased considerably with the increase of freeze-thaw cycles. After more than nine freeze-thaw cycles, these four parameters tended to be stable. These parameters increased with the increase of dry density and decreased with the increasing moisture content, except for the residual strength which did not exhibit any clear variation with an increase in moisture content. The residual strength, however, generally increased with an increase in dry density. The soil structural damage caused by frozen water expansion during the freeze-thaw is the major cause for the changes in mechanical behaviors of cohesive coarse-grained soils. With results in this study, the deterioration effect of freeze-thaw cycles on the mechanical properties of soils should be considered during the slope stability analysis in high-altitude mountain regions.

冻融循环作用下高寒地区粗粒土的力学和电学特性

为评价冻融影响下高寒地区粗粒土的工程特性,对不同干密度(ρd=1.90 g/cm^3,2.00 g/cm^3,2.15 g/cm^3)、不同含水率(w=9.0%,11.5%,14.0%)的粗粒土在不同冻融循环(C=0~20次)下电学和单轴力学特性进行试验研究。结果表明,循环冻融作用下,低密度、高含水(ρd=1.9 g/cm^3,w=14.0%)试样的应力-应变关系从应变硬化型向软化型过渡。随着冻融循环次数的增加,试样的电阻率(ρ)呈增长趋势,而单轴力学特性(单轴抗压强度qu、变形模量E)和脆性指标(IB)均显著衰减,在7~9次循环后趋于稳定。此外,冻融循环对试样的影响还受干密度和含水率的交互作用。采用图像法深入分析了冻融作用下粗粒土的剪切破坏和孔隙结构特征。在修正的Archie模型的基础上,提出了考虑冻融影响的非饱和含粘粒粗粒土的电阻率模型来评价试样电学特性的冻融效应。最后,建立了冻融粗粒土的单轴抗压强度、变形模量和电阻率的关系,对基于无损的电阻率法评价冻融粗粒土力学特性具有重要意义。