Study on discrete seepage model for fractured rock masses
Date Issued
2008
Date
2008
Author(s)
Chiang, Chih-Wei
Abstract
It is crucial to well know on the behaviors of rock masses for underground utilization, such as the tunnel, radioactive waste material store and the liquefied naturalas stores etc., all need to build the appropriate model for the description of behaviors of rock masses, so as to estimate, analyze, predict or control all sorts of projectehaviors. Traditionally, the behavior of rock masses can be described specifically in accordance with the characteristic of handling problem such as thermal field, flow field, mechanical field or chemical field. However, the problems of flow field and mechanical field always lead the security of fractured rock engineering. Therefore, the appropriate prediction on the flow rate, stress and deformation of fractured rock masses, i.e., theydro-mechanical coupled behavior, is not only the base for engineering design, but also the key point for its performance assessment.n this study, the 2-D discrete fractured networks (DFN) model was performed through MATLAB programming language. The discrete fractured networks model was generated according to geometric parameters of fractures, such as the locations of centers of fractures, trace lengths, orientations and apertures, and they also follow theirwn distribution type. Furthermore, the flow field in the rock was solved using Darcy’s Law and mass-balance equation with specified boundary conditions. Then, it based on the concept of equivalent continuum to obtain the hydraulic conductivity of a zone which was selected by users. On the basis of this model, this research considers the permeability of rock mass and to probe into their influences on the mechanical and hydraulic behaviors.sers can select the theories of hydraulic behavior or hydro-mechanical coupled behavior free in this 2-D discrete fractured networks model. Using the theory ofydraulic behavior, it will calculate with hydraulic apertures instead of mechanical apertures. Using the theory of hydro-mechanical coupled behavior, it not only employs mechanical apertures to advance the accuracy compared with using the theory of hydraulic behavior, but also probe into the variations of permeability of rock massaused by stresses changing. Under analytic process, users also can freely choose the zone and size which they want to observe and obtain the hydraulic conductivity of rockass in the zone. Utilizing this way which freely choose the zone and size, we can obtain the size of representative volume element (RVE) exactly. Additionally, the permeability of fractured rock mass would cause the permeability anisotropy with the change of stresses. Thus this research also probe into the change of permeabilitynisotropy caused by overburdenend and caused by parameters.he results of study show that when the compressed normal to the joint, JRC and JCS would affect the hydraulic conductivity. And the accuracy of JRC will be a keyactor. Under shear loading, the residual friction angle affects the hydraulic behavior of VII joints hardly. The hydraulic conductivity tends toward stability when the overburden is deep to certain depth. Utilizing the way which the observed zone’s size and position cooperate each other, the size of representative volume element (RVE) would be obtained exactly. The observed zone’s size chooses smaller, the more variable hydraulic conductivity is. The observed zone’s size chooses larger, the more steady hydraulic conductivity tends toward. The density of spacing is lower, the larger range of steady size is. The density of spacing is higher, the higher k value is. The trace length is longer, the smaller range of steady size is. The trace length is shorter, the larger range of steadyize is. The coefficient of lateral earth pressue and JRC could cause the permeability anisotropy with the change of overburdened, but the orientation of fractured rock massnfluence the permeability anisotropy smaller.
Subjects
fractured rock masses
2-D discrete fractured networks (DFN)
hydro-mechanical coupled behavior
representative volume element (RVE)
anisotropic permeability
Type
thesis
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