岩體通常由異質岩石材料及大量的不連續面所組成，其工程性質與構成岩體之各成分材料的性質及不連續面特性有密切關連。此種特質使得岩體具有尺度相依性、空間相依性及方向相依性。在岩石力學及水文地質學領域，常將異質性裂隙岩體經均質化或升尺度後，視為等值連續體。表徵單元體的概念是利用連續體理論的先決條件及探究評估岩體在多重尺度下各種性質的基礎，本計畫目標旨在建立決定裂隙岩體裂隙程度、水力傳導係數及力學性質表徵單元體尺寸的方法及程序。針對裂隙程度的表徵單元體尺寸，本計畫採用解析及數值方法求解。幾何參數隨岩體尺寸而變動的情形，透過統計學方法加以量化描述。解析解的結果將進一步與數值方法及案例研究加以驗證。水力傳導及力學性質之表徵單元體尺寸及等值性質方面，則採用合成岩體模式進行分析。結合FracMan生成離散裂隙網絡及 PFC3D鍵結顆粒模式及平滑節理模式，構成合成岩體，並進行一系列不同尺寸合成岩體力學及水力傳導試驗。不同尺寸裂隙岩體幾何參數、力學及水力傳導之變異係數將可由統計方法求得。以可接受變異係數為基礎，可決定裂隙岩體之幾何、力學及水力傳導係數之表徵單元體尺寸。 ;Rock masses commonly consist of heterogeneous rock materials and a large number of discontinuities. The engineering behaviors of a rock mass thus depend on the ensemble properties of rock materials and discontinuities. Given these, rock masses usually possess the characteristics of scale-dependency, spatial dependency, and directional dependency. Homogenizing or upscaling a heterogeneous rock mass to an equivalent continuum approximation is usually adopted in the evaluation of rock masses in the fields of rock mechanics and hydrogeology. The concept of the representative elementary volume (REV) is the premise of the continuum method and the basic to the evaluation of rock masses in a multiscale approach. The goal of this proposed study is to develop the methodology and procedure to quantify REVs of fracture intensity, hydraulic conductivity, and mechanical properties of fractured rock masses. To determine the REV of fracture intensity, both analytical and numerical approaches will be employed. The variation of geometrical parameters with varied sample sizes will be quantified by statistical analysis. The results of analytical approach will be verified by discrete fractured network model with selected cases studies. For the properties of hydraulic and mechanical REV and equivalent continuum of fractured rock masses, the synthetic rock mass (SRM) model will be adopted in this study. The SRM model will be generated by using the discrete fracture network (DFN) created by FracMan, the bonded particle model and smooth-joint model of PFC3D, and the results of mechanical and hydraulic tests with various sample sizes. The coefficient of variation of geometrical, mechanical, and hydraulic properties will be determined statistically from the results of the mechanical and hydraulic tests. Then the REVs for geometrical, mechanical and hydraulic properties are determined at acceptable coefficient of variation.
