高围压下砂土的渗透特性试验研究

利用高压三轴渗透试验系统,对某矿区深部的粗砂和细砂进行了高围压条件下的渗透试验。研究了同一水力梯度下渗透系数与围压的关系;同一围压下渗透系数与渗透水力梯度的关系;同一水力梯度下,围压逐级加载的渗透系数与一次加载的渗透系数之间的差别。结果表明,粗砂和细砂在同一水力梯度下渗透系数均随围压的增大而逐渐减小,在同一围压下,渗透系数会随渗透水力梯度的增大而逐渐增大;同一水力梯度下,围压逐级加载下的渗透系数明显小于一次加载条件下的渗透系数。根据围压与渗透系数的关系拟合出了两种砂样渗透系数与围压关系的数学表达式。为探究高围压下渗透系数变化的原因,研究了砂样试验过程中的体积变化和试验前后的粒度成分变化。结果表明,围压的施加过程伴随着试样的体积减小,相应的孔隙度减小,渗透系数降低;高围压条件下,砂土颗粒被挤碎成细颗粒,使得砂土的细粒含量增多,孔隙度减小,导致了砂土渗透系数的降低。

Experimental investigation of hydraulic conductivity of sand under high confining pressure

This paper presents an experimental investigation on hydraulic conductivity of coarse and fine sands from a deep underground mine under high confining pressures using a static triaxial permeability test system. A series of experiments for hydraulic conductivity is performed under high confining pressures to investigate the correlation between the hydraulic conductivity and the confining pressure in the same hydraulic gradient, the relationship between the hydraulic conductivity and hydraulic gradient in the same confining pressure, the differences between hydraulic conductivities from the confining pressures by stepwise loading test and the direct loading test under the same hydraulic gradient. The results show that the hydraulic conductivity of the coarse sand and fine sands are all gradually decreased with the increasing confining pressure under the same hydraulic gradient. Under the same confining pressure, the hydraulic conductivity of the sand increases gradually with the increasing hydraulic gradient. It is also found that the hydraulic conductivity of the sand with stepwise loading is much higher than that with the direct loading under the same hydraulic gradient. The volume change and grain size compositions of the sand sample before and after the test are studied to find the reason why the hydraulic conductivity changes with the confining pressure. The results indicate that the volume of the sand sample decreases during the process of confining pressure increasing and permeation, which lead to the decreasing hydraulic conductivity. The grain size compositions of the sand samples before and after the permeability test show that some sand grains are crushed under high confining pressure, which increase the finer particles and decrease the porosity of the sample therefore decrease the hydraulic conductivity.