冻融循环过程中土体的孔隙水压力测试研究

冻融循环对土的结构以及物理力学性质有着重要影响，其变化与冻融过程中的孔隙水压力变化有密切关系。但土体冻结过程中的孔隙水压力测试一直是冻土土工测试试验的技术难题。针对这一难题，研发了一种适用于冻结土体孔隙水压力测试的探头，并对砂土和粉质黏土在冻融循环过程中的孔隙水压力发展变化进行了实时监测，获得了圆柱试样冻融循环过程中不同深度处的孔隙水压力变化过程。在冻结过程中，粉质黏土形成冻结缘区及可视的分凝冰，而砂土则无冻结缘及分凝冰的形成。冻融循环过程中土体内部的孔隙水压力变化受温度、冻结速率、冻融循环以及土质等因素的影响。孔隙水压力随温度的循环变化而经历周期性变化：冻结过程中，孔隙水压力不断下降，吸力不断增加；融化过程中，孔隙水压力增大。而冻结速率、冻融循环及土质主要对孔隙水压力降的幅值变化产生影响。此外，冻结锋面位置附近孔隙水压力的下降、吸力的增加，正是水分由未冻区向冻结区迁移的主要驱动力。根据以上试验结果及其理论分析发现，所研制的孔隙水压力探头具有一定的实用性。

Pore water pressure measurement for soil subjected to freeze-thaw cycles

The freeze-thaw cycles change the structure of soils and influence their physical and mechanical properties, which can in turn be closely related to the pore water pressure change. However, measuring the pore water pressure of freezing soils has always been a challenge task. Here a new pore water pressure probe is developed and used to measure variations of pore water pressures of sand and silty clay during freeze-thaw cycles, from which the pore water pressures at three different depths of a cylindrical specimen are obtained. It is found that the frozen fringe and some ice lens occur in the silty clay samples during freezing; while no frozen fringe and ice lens form in sand samples. The pore water pressure is influenced by temperature, freezing rate, freeze-thaw cycles, soil types and others. The pore water pressure experiences a periodical change during the freeze-thaw cycles. The pore water pressure decreases and suction increases gradually during freezing, whereas the pore water pressure increases during thawing. The freezing rate, freeze-thaw cycles and soil types can primarily influence the amplitude of pore water pressure drop. In addition, the pore water pressure drop and suction increase near the freezing front are the major driving force of water migration from unfrozen zone to frozen zone. The above results show that the pore water pressure probe can be effectively used to measuring the pore water pressure of frozen soils.