Modeling spatial fracture intensity as a control on flow in fractured rock |
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Authors: | Chen-Chang Lee Cheng-Haw Lee Hsin-Fu Yeh Hung-I Lin |
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Institution: | (1) Department of Resources Engineering, National Cheng Kung University, Tainan 701, Taiwan; |
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Abstract: | Spatial fracture intensity (P
32, fracture area by volume) is an important characteristic of a jointed rock mass. Although it can hardly ever be measured,
P
32 can be modeled based on available geological information such as spatial data of the fracture network. Flow in a mass composed
of low-permeability hard rock is controlled by joints and fractures. In this article, models were developed from a geological
data set of fractured andesite in LanYu Island (Taiwan) where a site is investigated for possible disposal of low-level and
intermediate-level radionuclide waste. Three different types of conceptual models of spatial fracture intensity distribution
were generated, an Enhanced Baecher’s model (EBM), a Levy–Lee Fractal model (LLFM) and a Nearest Neighborhood model (NNM).
Modeling was conducted on a 10 × 10 × 10 m synthetic fractured block. Simulated flow was forced by a 1% hydraulic gradient
between two vertical x–z faces of the cube (from North to South) with other boundaries set to no-flow conditions. Resulting flow vectors are very
sensitive to spatial fracture intensity (P
32). Flow velocity increases with higher fracture intensity (P
32). R-squared values of regression analysis for the variables velocity (V/V
max) and fracture intensity (P
32) are 0.293, 0.353, and 0.408 in linear fit and 0.028, 0.08, and 0.084 in power fit. Higher R
2 values are positively linked with structural features but the relation between velocity and fracture intensity is non-linear.
Possible flow channels are identified by stream-traces in the Levy–LeeFractal model. |
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Keywords: | |
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