Study on long-term permeability of fracture in rock mass

为了预测和控制岩体中裂隙的长期渗透率，必须明确地下裂隙的渗透率随时间的变化。本研究的目的是建立一种预测裂缝长期渗透率的方法。为此，首先进行了恒定法向应力下粗糙表面裂缝随时间闭合的理论研究。其次，采用所提出的压痕试验系统对岩石的松弛模量进行了测量。最后，从实验和理论两方面阐明了岩石在剪应力和正应力作用下裂隙渗透率随时间的变化规律。主要研究结果如下：1)基于孔径局部极小值及其半径的分布，导出了恒定正应力与随时间变化的闭合关系公式。结果表明，在恒定的法向应力作用下，岩石的法向应力-弹性闭合曲线和松弛模量可以估计出岩石的最终闭合。如果弹性闭合与正应力的对数呈线性关系（古德曼骨折），则最终的时变闭合与正应力无关。2)开发了用于估算岩石松弛模量和弹性常数的压痕试验系统。利用断裂模型和测量的松弛模量，对恒定法向应力下断裂随时间的闭合进行了蒙特卡罗模拟。定性结果表明，花岗岩的时效闭合不依赖于正应力，砂岩的时效闭合依赖于正应力。然而，模拟的随时间变化的闭合比实验结果要小得多。认为这种差异是由于接触面积的不同而产生尺寸效应的主要原因。3)进行了围压条件下恒定/均匀法向应力剪切变形裂缝渗透性试验。少

For prediction and control of the long-term permeability of a fracture in rock mass, it is indispensable to clarify permeable change of an underground fracture with time. The purpose of this study is to establish a method for prediction of long-term permeability of a fracture. For this purpose, firstly, it was carried out that theoretical study of time-dependent closure of a fracture with rough surfaces under constant normal stress. Secondary, the relaxation modulus of rock was measured by using proposed indentation-test system. Finally, the permeable change of a fracture in the rock under both of shear stress and normal stress with time was clarified experimentally and theoretically.Main results obtained in this study are summarized as follows:1) A formula for the relationship between constant normal stress and time-dependent closure as a function of time was derived, based upon the distributions of aperture local minima and their radii. It was shown that the ultimate closure of a fra … More cture under constant normal stress can be estimated from the normal stress-elastic closure curve and the relaxation modulus of rock. The ultimate time-dependent closure was shown to be independent of the normal stress if the elastic closure is linear with the logarithm of the normal stress (Goodman's fracture).2) Indentation-test system for estimating the relaxation modulus and the elastic constant of rock was developed. A Monte Carlo simulation on time- dependent closure of a fracture under constant normal stress was performed by using the fracture model and the measured relaxation modulus.The results qualitatively showed that the time-dependent closure for granite is not dependent on normal stress and that for sandstone is dependent on normal stress. However, simulated time-dependent closure was fairly smaller than that of experimental results. It was thought that this difference was the main causes with the size effect by the difference of contact area.3) Permeability test of a fracture applying shear deformation with constant/uniform normal stress under confining pressure was carried out. Less