压力溶解和自由面溶解/沉淀对双重孔隙岩体中热-水-应力耦合影响的有限元分析

摘要

The models of pressure solution and free-face dissolution/precipitation are introduced in the study. Aiming at a hypothetical nuclear waste repository in a saturated dual-porosity fractured rock mass, three computation cases are designed: (1) fracture aperture is a function of pressure solution and free-face dissolution/precipitation; (2) fracture aperture changes only with pressure solution(the matrix porosity of bedrock is also a function of stresses in these computation two cases); (3) fracture aperture and matrix porosity are constants. Then the corresponding two-dimensional finite element analysis of the coupled thermo-hydromechanical processes are carried out; and the states of temperatures, fracture apertures and permeabilities, pore water pressures, flow velocities and stresses in the rock mass are investigated. The results are as follows: the absolute values of increments of fracture aperture and relevant permeability caused by free-face dissolution/ precipitation are obviously larger than those of fracture aperture and relevant permeability caused by pressure solution; and the effects of pressure solution on fracture aperture and relevant permeability are less. The fracture apertures and relevant permabilities modified by combined action of pressure solution and free-face dissolution/ precipitation are about 1.5 and 7.0 times of those modified only by pressure solution, respectively. Under the action of temperature field from released heat, the fracture water pressures in the computation domain rise first, then drop again, but the change extents are not large. The differences between the magnitudes and distributions of stresses within rock mass in the three calculation cases are very small.%引入裂隙开度的压力溶解和自由面溶解/沉淀模型,针对一个假设的位于饱和双重孔隙-裂隙岩体中的高放废物地质处置库,拟定3种计算工况:(1)裂隙开度是压力溶解和自由面溶解/沉淀的函数；(2)裂隙开度仅随压力溶解而变化(这2种工况中基岩的孔隙率亦是应力的函数)；(3)裂隙开度和基岩的孔隙率均为常数,进行热-水-应力耦合的二维有限元分析,考察岩体中的温度、裂隙开度及渗透系数、孔隙水压力、地下水流速和应力的变化、分布情况.结果表明:自由面溶解/沉淀引起的裂隙开张及渗透系数增量的绝对值要明显大于压力溶解产生的裂隙闭合及渗透系数减量的绝对值,而压力溶解对裂隙的开度及其渗透系数的影响较小；同时计入压力溶解和自由面溶解/沉淀相比于仅考虑压力溶解,同时计入压力溶解和自由面溶解/沉淀的裂隙开度及其渗透系数分别约为仅考虑压力溶解时的1.5和7.0倍；在释热温度场的作用下,计算域中的裂隙水压力随时间先上升再下降,但变化幅度不大；3种工况下岩体中的应力量值及分布差别很小.