针对寒区建设工程在土体冻结作用下的地基与基础稳定性问题,采用冻胀敏感性粉质黏土开展了土体冻结过程中的物理力学特性试验研究,获得了起始冻胀含水率、冻胀力、高温冻土抗剪强度等参数及其变化规律。主要结论如下:当土体含水率小于起始冻胀含水率时产生冻缩现象,由土骨架遇冷收缩和孔隙水相变膨胀共同作用所致;不同含水率条件下,土样冻结竖向位移经时变化曲线分为“冻缩”“冻缩-回弹”“冻缩-冻胀”3种类型;冻胀力经时变化曲线受温度场发展的影响分为快速增长和稳定增长2个阶段;冻胀力随冻结温度的降低而增大,利用分凝势理论进行分析,土体主动区温度梯度增大是冻胀力增大的原因;与常温土样相比,-3 ℃条件下的某冻结粉质黏土的黏聚力由7.34 kPa增加到29.56 kPa,内摩擦角由6.40°增加到9.18°,但其剪应力变化曲线并没有表现出低温冻土常见的脆性破坏,而是呈现应变硬化特征。
Abstract
To address the issue of foundation stability in construction engineering in cold regions, an experimental study was conducted to investigate the physical and mechanical properties of a frost susceptible silty clay in freezing process. Parameters such as the critical water content for frost heaving, frost heave forces, and shear strength of warm frozen soils were determined. The results indicate that frost shrinkage occurs when the water content of soil samples is below the critical water content for frost heaving. This phenomenon is attributed to the combined effect of frost shrinkage of the soil skeleton and phase transformation of pore water. The vertical displacement curves of soil samples exhibit three types with varying water content: frost shrinkage, frost shrinkage followed by rebound, and frost shrinkage followed by frost heave. The curve of frost heave forces can be divided into two stages, namely rapid growth and stable growth, due to the development of the temperature field. The frost heave force increases as the freezing temperature decreases. The increase in temperature gradient within the active zone of freezing soils, based on the theory of segregation potential, is the cause of higher frost heave forces. When compared to soil samples at normal temperature, the cohesion of frozen silty clay at -3℃ increased from 7.34 kPa to 29.56 kPa, and the internal friction angle increased from 6.40° to 9.18°. However, the shear stress curves did not exhibit brittle failure of frozen soils, but rather displayed characteristics of strain hardening.
关键词
粉质黏土 /
高温冻土 /
起始冻胀含水率 /
冻胀力 /
抗剪强度
Key words
silty clay /
warm frozen soils /
critical water content for frost heaving /
frost heaving force /
shear strength
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基金
国家自然科学基金面上项目(41271096);中国博士后科学基金面上资助项目(2021M703507);江苏省产学研合作项目(BY2021208);深部岩土力学与地下工程国家重点实验室开放基金项目(SKLGDUEK1704);江苏省高校哲学社会科学研究一般项目(2022SJYB1316)
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