考虑分形特征的节理面渗流计算模型

SEEPAGE CALCULATION MODEL FOR ROUGH JOINT SURFACE CONSIDERING FRACTAL CHARACTERISTICS

粗糙表面对节理渗流影响显著,但难以定量描述,几何分形作为描述岩石节理表面形貌特征的一种方法,近年来得到了广泛应用。为了准确表述节理表面粗糙形态对节理渗流的影响,基于节理接触面积和开度,结合节理面分形特征影响,建立节理面水力开度计算分形修正公式。以自然节理试件为原型预制类岩石材料节理试件,通过激光测试获取节理表面三维形貌数据,应用立方体覆盖法计算节理试件的分形维数,并进行剪切–渗流耦合试验,计算剪切试验过程中水力开度变化规律。同时计算节理试件平均开度以及接触面积比在剪切过程中的变化规律,并应用Zimmerman计算公式、Yeo修正计算公式和分形修正公式分别计算节理面的水力开度,将计算结果与实测值进行比较。分析表明:分形修正公式与试验测试值吻合较好,实现了节理面接触面积、节理开度和节理面分形维数的良好耦合,能更为全面地描述节理面的渗流特性,具有较好的适用性。

Understanding hydro-mechanical behavior of single rock joints is a basic building block to assess several important properties of jointed rock mass associated with fluid flow,a representative one among which is mass transport in rock mass. The surface roughness plays an important role in the fluid flow behavior through a single rock joint,which has received extensive studies in the past a few decades,by using various approaches,such as JRC,statistical parameters and fractal dimension. An improved equation involving the relation between mechanical aperture and hydraulic aperture,with the employment of the fractal dimension of joint surface was proposed to evaluate the effects of surface roughness on the behavior of fluid flow through rock joints. To verify this equation,a number of coupled shear-flow tests for several artificial rock joint specimens with the surface characteristics of natural rock joints were carried out,and the evolution of mechanical and hydraulic apertures during shear processes were evaluated. The fractal dimension of each specimen was calculated using cubic covering method based on the measured surface topographical data. Compared with other commonly used equations,such as Zimmermans equation and Yeos correction equation,the proposed equation gives better fitting to experimental measurements,which may serve as an effective approach for quantitative estimation of the hydro-mechanical behavior of rock joints.