冻融循环对冻土-混凝土界面冻结强度影响的试验研究

为研究冻融循环作用对冻土-混凝土界面冻结强度的影响,对不同冻融循环次数、法向应力、试验温度及土体初始含水率条件下的冻结界面进行了系列直剪试验,研究经历冻融循环后界面峰值剪切强度、残余剪切强度及强度参数的变化规律。试验结果表明:冻融循环对界面剪切应力与水平位移曲线形态影响很小,经历20次循环后曲线仍是应变软化型。冻融循环对峰值剪切应力的影响强于对残余剪切应力的影响,表明其对界面胶结冰含量产生影响。当土体初始含水率较低且温度较高时,冻融循环使界面峰值剪切强度增加,但变化量较小。然而在含水率较高(20.8%)及试验温度较低时(-5℃),峰值剪切强度随着冻融循环增加而降低。因此在土体含水率较高且冻结温度较低时,对于发生小变形的冻结界面需要重视冻融循环对峰值剪切应力的影响。不同初始含水率、试验温度下冻融循环对残余剪切强度的影响较小且变化规律不明显。在试验温度为-1℃,-3℃,-5℃时,峰值黏聚力随冻融循环增加分别表现为增加、波动和下降,推测是由于界面胶结冰含量不同而引起。峰值摩擦角和残余摩擦角随冻融循环次数增加略有变化。

Experiment study on effects of freeze-thaw cycles on adfreezing strength at frozen soil-concrete interface

In order to study the effects of freeze-thaw cycles on the adfreezing strength between frozen soil and concrete interface, a series of direct shear tests are conducted with different numbers of freeze-thaw cycles under different normal stresses, test temperatures and initial water contents. The peak shear strength, residual shear strength, shear strength parameters are used to analyze the adfreezing strength at the interface. The test results show that the shear behaviors of the interface are still strain-softening after 20 cycles. The influences of freeze-thaw cycles on the peak shear stress are stronger than those on the residual shear stress, indicating that they have an effect on the content of ice crystal of the interface. When the water content of the soil is low and the test temperature is high, the peak shear strength lightly increases with the increasing cycles, and it decreases obviously at water content of 20.8% and test temperature of -5℃. Therefore, it is necessary to pay attention to the influences of freeze-thaw cycles on the peak shear stress under high water content, low test temperature and small deformation of the structural interface. The cycles have few influences on the residual shear stress. The peak cohesions of the interface increase, become stable and decrease with the increasing cycles at the test temperature of -1℃, -3℃ and -5℃, respectively, which is presumed to be caused by the water migration of the soil near the interface. The peak and residual interface friction angles are influenced slightly by the cycles.