冻结环境温度对粉质黏土冻融循环效应影响的试验（英文）

Experiment of freeze-thaw cycling effect on silty clay under different environmental freezing temperatures

为明确冻结过程中环境温度对土体冻融循环效应的影响规律,以青藏高原粉质黏土为对象,首先选择冻结环境温度(-5℃、-10℃、-15℃、-20℃、-25℃、-30℃)和冻融循环次数(0、1、3、6、9、12、15)为变量进行了一系列冻融循环试验,然后,以围压(50、100、150kPa)为变量,对经历冻融循环试验后的试样进行三轴压缩试验。研究结果表明:冻结环境温度会显著影响土体经历冻融循环后的物理力学性质。冻融循环后试样的破环强度整体上有所减小,并随冻结环境温度的降低呈先减小、后增大的变化规律,-15℃时破坏强度达谷值。虽然土体冻结后的表观体积增大,但膨胀变形分量和收缩变形分量在冻结过程中同时存在,而且随着环境温度的降低,冻胀先于冻缩达到极限状态,因此表观体积呈先增大、后减小的变化规律,相应地破坏强度呈相反的变化规律。此外,随着冻融循环次数的增加,破坏强度呈先减小、后逐渐稳定的变化规律。同时,冻结环境温度越低,破坏强度达到稳定值所需的冻融循环次数越少。试样冻结过程中的水分迁移速率和迁移量随环境温度的降低而减小,水分迁移对土体结构的影响也随之减小。抗剪强度指标表现为与破坏强度一致的冻融循环效应,其中内摩擦角对冻结环境温度变化的响应程度大于黏聚力的影响程度。

In order to study the influence of freezing temperature on freeze-thaw cycling of soil,a set of triaxial tests were conducted under different confining pressures（50,100,150kPa）for samples based on silty clay from Qinghai-Tibet Plateau regarding different freeze-thaw cycle numbers（0,1,3,6,9,12,15 times）under different freezing temperatures（-5℃,-10℃,-15℃,-20℃,-25℃,-30℃）.The results show that the level of freezing temperature considerably affects the soil freeze-thaw cycling.The failure strength decreases when freezing temperature changes from -5℃ to -15℃,and increases when freezing temperature changes from -15℃ to -30℃.Though volume of the surface increases under frozen condition,expansion and contraction coexist in freezing process.With the decrease of freezing temperature,it is earlier for expansion to reach the limit than contraction.Meanwhile,with the increase of freeze-thaw cycle number,the failure strength decreases dramatically,and then keeps constant.The failure strength achieves the relative stability index with less cycling times,when freezing temperature is lower.The migration rate inside samples becomes less when freezing temperature is lower,thus the amount of water migration correspondingly becomes less.Apparent shear strength parameters vary in the same regularity as failure strength,internal friction angle suffers a more significant effect on the freezing temperature than cohesion.