砂岩三轴循环加卸载条件下的渗透率研究

渗透率是地下工程的流-固耦合分析中的一个关键因素。对多孔红砂岩进行了三轴压缩试验，在不同变形阶段实施了轴向应力循环加卸载，并在试验全过程中测量轴向渗透率，得到了试样破坏全过程的渗透率演化规律。从平均应力和循环加卸载对渗透率的影响等两方面进行了深入分析，结果表明，（1）随着轴向变形的增加，初始压密阶段和弹性变形试样渗透率均匀减小；进入塑性变形阶段，渗透率与轴向变形的曲线逐渐趋于水平，低围压条件下渗透率略有增加。（2）轴向加载使骨架颗粒被压缩，引起孔隙减小，造成渗透率减小；采用经验公式定量描述了渗透率和平均应力之间的关系。（3）轴向应力循环加卸载过程中，骨架颗粒的不可恢复变形引起渗透率产生不可恢复现象。（4）峰值后渗透率只发生少许突跳，说明对于多孔砂岩，孔隙和裂隙对渗透率的影响相当，且渗透率的突跳程度随着围压的升高而降低。

Study of permeability of sandstone in triaxial cyclic stress tests

Permeability is one of the key factors in hydro-mechanical coupling study for underground engineering. A series of cyclic triaxial compression tests were conducted with red porous sandstones; the axial permeability was calculated according to Darcy’s law during the failure process. Based on the mechanical and permeability results, the influences of mean stress and stress cycles on permeability were investigated according to stress-strain curves and deformation modulus evolutions. Some conclusions are drawn: (1) With the increase of axial strain, permeability is consistently decreased in initial compaction and elastic deformation stages; during the plastic deformation stage, the reduction ratio of permeability is gradually decreased; in the end, permeability is even increased under low confining pressure. (2) The skeleton grain compaction causes porosity decrease, consequently permeability decreases; an empirical function is proposed to describe the relationship between permeability and mean stress. (3) During the stress cycles, the irreversible permeability behavior is induced by the irreversible deformation of skeleton grains. (4) There is a weak augment of permeability in post-peak stage, which shows the effect of induced cracks corresponds with the one of pore, the augment extent has a negative correlation with confining pressure, for porous sandstone.