冻结砂土三轴试验中颗粒破碎研究

压力作用下颗粒发生破碎是引起砂土力学特性变化的重要因素之一,冻结砂土也是如此。对冻结砂土进行了不同温度和围压下的三轴剪切试验,并筛分得到三轴试验前后的颗粒大小分布曲线。通过引入Hardin定义的颗粒破碎率Br,分析了围压与颗粒破碎的关系及颗粒破碎对冻土抗剪强度的影响。结果表明:在温度为-0.5℃,-1℃,-2℃,-5℃和围压为0.5,2,5,10 MPa的条件下,三轴剪切过程中会产生较为可观的颗粒破碎;颗粒破碎率Br随围压增大,到达一定围压后Br不再随着围压的增大发生明显变化,即存在一个颗粒不再发生明显破碎的临界围压σr。结合前人研究发现,-5℃下一般工程关心的围压范围内压融对冻土力学特性没有显著影响,而颗粒破碎起控制性作用。分析表明:-5℃条件下在不同的围压范围颗粒破碎对抗剪强度具有不同的影响。试验所采用的围压范围内,随着围压的增大,颗粒破碎率增大使得冻土的抗剪强度降低;破碎率达到极限以后,由于破碎的颗粒重排列又导致抗剪强度有所提高。

Particle crushing of frozen sand under triaxial compression

Particle crushing is one of the important factors to change mechanical properties of frozen sand, which is hardly studied quantitatively so far. Triaxial compression tests are carried out on a saturated frozen sand at -0.5℃, -1℃, -2℃ and -5℃ under the confining pressure of 0.5, 2, 5 and 10 MPa, respectively. The particle crushing ratio, B_r, defined by Hardin is obtained through the particle-size distribution curves for samples before and after triaxial tests. It aims to analyze the relationship between confining pressure and particle crushing as well as the influence of the particle crushing on strength. The testing program presents a considerable particle crushing in triaxial compression of the frozen sand. There is a critical confining pressure σ_r. When σ₃<σ_r, the particle crushing ratio, B_r, increases with the increase in confining pressure; otherwise, B_r does not increase obviously with the increase in confining pressure. Previous studies as well as the test results from this work show that under -5℃, pressure melting does not play important roles in mechanical properties of frozen soils. Therefore the test results under this temperature are taken for analysis without considering pressure melting. It is found that particle crushing has a dual influence on the strength of frozen sand. Under low pressure levels, particle crushing leads to weakening and strength decreases; with the increase in pressure, particle crushing reaches the maximum and particle rearrangement tends to improve the strength.