Developing on Permeability Tensor for Fractured Rocks
Date Issued
2014
Date
2014
Author(s)
Lin, Po-Yu
Abstract
Before underground excavation, engineers have to build a suitable model describing the behavior of rock masses to predict and analyze all sorts of possible engineering problems. Generally speaking, the behavior of rock masses should be described specifically in accordance with the characteristic of the engineering project such as mechanical field, thermal field, flow field or chemical field. However, every field not only affect the corresponding behavior for rock masses, but also influence each other. For tunnel excavation projects, flow field and mechanical field control the engineering stability in most cases. Therefore, appropriate prediction on the coupled hydraulic-mechanical behavior related to permeability, stress and strain relationships of fractured rock masses become an important issue to ensure the safety of tunnel engineering.
This study utilize the Discrete Fractured Network (DFN) model of Chiang (2008) to describe fractured rock mass, and propose an approach to obtain its permeability tensor. In order to obtain a reasonable permeability tensor, a rotary sampling method is constructed to observe the directionality of permeability. To improve the efficiency of rotary sampling method, a 2-steps sampling method is also proposed, which reduces the sampling time from several hours to thirty minutes only.
Finally, this study proceeds a parameter study base on the discussion of the results mentioned above. The continuum model is used to figure out the change in permeability tensor under different apertures and dip angles. Theoretically, the kxy and kyx of models with two sets of orthogonal fractures should be zero. In the other hand, the discrete model is utilized to observe the change of permeability tensor in different stress paths. All series of tests indicate that the rotary sampling method provides great approximation on computing permeability tensor of discrete fractured networks.
Subjects
離散裂隙網絡
旋轉取域
滲透係數張量
代表性體積元素
水力-力學耦合
Type
thesis
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