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，弄清地下裂隙的渗透率随时间的变化是必不可少的。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，首先对恒法向应力作用下粗糙表面裂纹的时间依赖闭合进行了理论研究。其次，利用所提出的压痕测试系统测量了岩石的松弛模数。最后，从实验和理论上阐明了岩石中裂隙在剪应力和正应力作用下的渗透性随时间的变化规律。本文的主要研究成果如下：1)基于孔洞局部极小值及其半径的分布，推导了恒定正应力和随时间变化的闭合度随时间变化的公式。结果表明，FRA…的最终关闭从岩石的法向应力-弹性闭合曲线和松弛模数可以估算出在恒定正应力作用下的更多裂缝。如果弹性闭合与正应力(古德曼断裂)的对数成线性关系，则最终的随时间变化的闭合与正应力无关。2)研制了用于估算岩石松弛模数和弹性常数的压痕试验系统。利用该断裂模型和测得的松弛模数，对恒正应力作用下裂隙随时间变化的闭合进行了蒙特卡罗模拟，定性地表明花岗岩的随时间变化的闭合与正应力无关，砂岩的随时间变化的闭合与正应力有关。然而，模拟的时间依赖闭合比实验结果要小得多。认为这种差异是接触面积不同而产生尺寸效应的主要原因。3)进行了围压作用下正应力恒定/均匀剪切变形裂缝的渗透性试验。较少

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