应力对岩石中孔隙流体压力的影响和地下水位震前异常变化机理

THE EFFECT OF STRESS ON PORE PRESSURE IN ROCKS AND THE MECHANISM OF WATER TABLE ANOMALY BEFORE EARTHQUAKES

在不同的围压和初始孔隙压力作用下,对孔隙岩石试件进行了不排液的三轴压缩试验,观测了轴向应变和孔隙压力随差应力的变化.试验结果表明:在低差应力下,孔隙压力随差应力的增加而增加.在中等和高差应力下孔隙压力随差应力的增加而降低.在高差应力下,孔隙压力也会随差应力的大幅度降低而升高.基于上述试验,假定地下水位的震前异常变化是地壳岩石中差应力变化的反映.根据这种假定解释了唐山大震前震中及外围地区地下水位异常变化的特征.

Triaxial compressive experiments of porous rock samples were carried out under various confining pressure and initial pore pressure without drainage; axial strain and pore pressure were observed versus differential stress. The results of such experiments show that pore pressure increases with increase of differential stress at low differential stress; pore pressure decreases with increase of differential stress at media and high differential stress. Pore pressure also increases with large amplitude decrease of differential stress at high differential stress. Based on such experiments, it is suggested that water table anomaly before earthquakes reflects the change of differential stress in crustal rocks. The anomalous behavior of water tables in the epicentral and peripheral areas before the great Tangshan earthquake of July 28, 1976 are explained by such suggestion.