基于RFPA~(2D)-Flow软件对裂隙岩体渗透特性表征单元体的研究

大型水利水电工程多依附于高陡裂隙岩体边坡而建,而边坡的渗控结构成为研究重点。为进一步研究裂隙岩体渗透特性及其各向异性的影响因素,基于C语言程序,考虑不同迹长、密度的概率分布,通过蒙特卡罗方法生成随机裂隙,然后将随机裂隙导入有限元渗流计算软件RFPA~(2D)-Flow,形成渗流裂隙网络模型。通过对不同的方位、不同尺寸上的等效渗透系数的模拟计算,得到不同工况下的渗透张量,结合类张量特性和类常量特性判定依据,确定渗流表征单元体,并自定义渗透特性各向异性系数,研究裂隙的密度、迹长对岩体渗透张量、表征单元体尺寸和各向异性系数的影响。结果表明:①裂隙密度和裂隙迹长对裂隙岩体的渗透主值影响较大,但对渗透主方向几乎无影响,随密度或者迹长的增大,裂隙岩体的渗透主值逐渐增大;②在一定范围内,随着裂隙密度或迹长的增大,裂隙岩体的渗透表征单元体尺寸逐渐减小;③裂隙岩体渗透特性的各向异性系数r随密度增大逐渐减小,随裂隙迹长增大呈现先减小后增大的趋势。在此基础上,以锦屏一级水电站坝区左岸边坡裂隙岩体为例,根据地质勘探所获的裂隙概率分布特征及相关参数,利用本文研究方法进行渗流数值模拟计算,确定锦屏左岸裂隙岩体的渗透张量和表征单元体尺寸,并结合现场压水试验结果对本文数值模拟结果进行修正,修正系数在一个数量级之内,说明本文模拟计算结果与实测结果相近。

Study on the element volume of permeability characteristics in fractured rock mass based on RFPA2D flow

Large scale water conservancy and hydropower projects are mostly built on highly steep fractured rock slope,and the seepage control structure of the slope has become a key research subject.In order to further study the permeability characteristics of fractured rock mass and the influencing factors of its anisotropy,considering the probability distribution of different trace lengths and densities,the random cracks are generated by Monte Carlo method.After that the random cracks are imported into the finite element seepage calculation software RFPA2D Flow to form a seepage fracture network model.Simulated calculation of equivalent permeability coefficient in different directions and sizes could obtain the permeability tensor in different working conditions.Combining the approximate tensor property and approximate constant property as the criterion to determine the seepage characterization unit.Also,the permeability anisotropy coefficient could be customized to study the influences of different trace lengths and densities onto the permeability tensor,the characterized element sizes and the anisotropy coefficient.The results showed that:① the density and length of fractures have great influences on the principal permeability value of fractured rock mass,but have little influence on the principal direction of permeability.② With the increase of density or trace length,the principal permeability value of fractured rock mass increases gradually.Within a certain range,with the increase of fracture density or trace length,the size of characterization unit of fractured rock mass decreases gradually.③ The anisotropic coefficient of permeability characteristics r in fractured rock mass decreases with the increase of density,and decreases first and then increases with the increase of fracture trace length.Based on these results,this paper took the fractured rock mass on the left bank slope of Jinping I Hydropower Station Dam Area as an example to perform the seepage numerical simulated calculation based on fracture probability distribution characteristics and related parameters obtained from geological exploration.The permeability tensor and the size of characterization unit were determined from calculation,and were corrected based on on site water pressure test results.The correction coefficient is in one order of magnitude,which shows that the simulation results in this paper are close to the measured ones.