• Journal of the Korean Geotechnical Society
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• v.15 no.5
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• pp.217-228
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• 1999

The three methods of analysis (i) REV(representative elemental volume), (ii) non-REV and (iii) joint network analysis are introduced in this paper to analyze the groundwater flow in jointed rock mass and the inflow into underground excavations. The results from those methods are compared one another to reveal their characteristics by varying the number of joints and the diameter of the opening. The pre-processor, the so-called sequential analysis, is introduced to predict the equivalent hydraulic conductivity of a jointed rock mass having a number of intersecting joints. Using the finite element mesh, joint map and sequential analysis, the equivalent hydraulic conductivities are calculated for all 445 elements. The hydraulic inhomogeneity and the determination of the representative properties of jointed rock masses are discussed. In the REV analysis where the entire rock mass is homogenized through the representative properties, the inflow is increased regularly and consistently by increasing the joint density, the opening size and the conductivity contrast value. Though the non-REV analysis showed irregular variation of the inflow due to the local inhomogeneity allowed to individual elements, the inflow approached the REV results as the characteristic length increases. The joint network analysis showed the most sensitive reaction to the joint density, the opening size and the presence of the network crossing the opening. The reliability of the network analysis depends on the geometric data of individual joints. In view of the limited field data on joint geometry and possible uncertainty the REV and non-REV methods are considered more practical and rational than the joint network analysis.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.10a
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• pp.271-278
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• 1999

Soil filters are commonly used to protect the soil structures from eroding and piping. When filters are clogged by fine particles which are progressively accumulated, these may lead to buildup of excessive pore pressures also leading to instability in subsurface infrastructure. A filter in the backfill of a retaining wall, a filter adjacent to the lining of a tunnel, or a filter in the bottom of an earth dam can be clogged by transported fine particles. This causes reduction in the permeability, which in turn may lead to intolerable decreases in their drainage capacity. In this thesis, the extent of this reduction is addressed using results from both experimental and theoretical investigations. In the experimental phase, the permeability reduction of a filter is monitored when an influent of constant concentration flows into the filter (uncoupled test), and when the water flow through the soil-filter system to simulate an in-situ condition (coupled test), respectively. The results of coupled and uncoupled test are compared with among others. In the theoretical phase of the investigation, a representative elemental volume of the soil filter was modeled as an ensemble of capillary tubes and the permeability reduction due to physical clogging was simulated using basic principles of flow in cylindrical tubes. In general, it was found that the permeability was reduced by at least one order of magnitude, and that the results from the uncoupled test and theoretical investigations were in good agreement. It is observed that the amount of deposited particles of the coupled test matches fairly well with that of the uncoupled test, which indicates that the prediction of permeability reduction is possible by preforming the uncoupled test instead of the coupled test, and/or by utilizing the theoretical model.