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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 under pressure is one of the important factors that cause the change of mechanical properties of sand, as is frozen sand. Triaxial shear tests were carried out on the frozen sand at different temperatures and confining pressures, and the particle size distribution curve before and after the triaxial test was screened. The relationship between confining pressure and particle breakage and the influence of particle breakage on the shear strength of frozen soil are analyzed by introducing the particle breaking rate Br defined by Hardin. The results show that under the conditions of temperature of -0.5 ℃, -1 ℃, -2 ℃, -5 ℃ and confining pressure of 0.5, 2, 5 and 10 MPa, the triaxial shear process will produce more considerable particle crushing The Br breaking rate increases with the increase of confining pressure. When the confining pressure reaches a certain confining pressure, Br no longer changes obviously with the increase of confining pressure. That is, there exists a critical confining pressure σr at which no obvious particle breakage occurs. Combined with the previous studies, it was found that the pressure-melting within the confining pressure range concerned by general engineering at -5 ℃ had no significant effect on the mechanical properties of frozen soils, whereas the particle crushing played a controlling role. The analysis shows that the particle crushing has different effects on the shear strength under different confining pressure range at -5 ℃. Within the confining pressure range used in the experiment, as the confining pressure increases, the particle crushing rate increases so that the shear strength of the frozen soil decreases. When the crushing ratio reaches the limit, the shearing strength due to the rearranged crushed particles improve.