考虑应力状态的裂隙岩体渗透系数张量计算

Hydraulic Conductivity Tensor for Fractured Rock Mass Considering Stress State

渗透系数张量的正确确定是进行大范围裂隙岩体渗流计算的基础。以实测岩体不连续面的几何特征和统计参数为基础,利用立方定律计算渗透系数张量时,还必须进行裂隙粗糙度、裂隙网络连通程度的修正,并考虑应力变化对渗透系数的影响。对取自丹江口水库库区的辉绿岩剪切裂隙进行了不同围压和裂隙水压力下的渗透试验,结果表明:裂隙的渗透系数与净围压的关系符合指数函数特征,而随着裂隙水压力的增大,裂隙面两侧基岩发生附加变形,导致渗透系数增大。在此渗流试验的基础上对渗透系数进行考虑三向应力和裂隙水压力变化的修正后,得到新的渗透系数张量计算公式。对丹江口水库库区某段裂隙岩体渗透系数张量的计算实例表明,修正后的渗透系数张量更符合实际。

The hydraulic conductivity tensor is a set of parameters fundamental to the seepage analysis for large-scale fractured rock mass. Based on the geometrical characteristics and statistic parameters of discontinuities in rock mass obtained by means of field survey, the cubic law is usually used for the calculation of hydraulic conductivity tensor, and some modification must be made considering the roughness of the real discontinuities, the connectivity of the fracture network, and the influence of stress variation. Permeability tests under different confining pressure and fracture water pressure were carried out on diabase rock samples from Danjiangkou Reservoir to study the permeability characteristic of the shear fracture. The test results show that the permeability of fracture decreases with the increase of net confining pressure, following the law of exponential decay. While with the increase of fracture water pressure, the fracture permeability increases as well because of the enlargement of fracture aperture caused by the additional compression of the rock matrix. Thus, further modification considering stress variation was made based on the experimental data and a new calculation formula for the determination of hydraulic conductivity tensor was obtained. Results of calculation example of a certain section of fractured rock mass located in Danjiangkou Reservoir show that the calculated value of hydraulic conductivity tensor obtained by the new formula corresponds well with the field measured values.