Back Analytical Technique for Evaluating the Hydraulic Properties of Unsaturated Rock.

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  • 岩石の不飽和特性の逆推定法
  • ガンセキ ノ フホウワ トクセイ ノ ギャク スイテイホウ

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Abstract

Hydraulic properties of unsaturated rock, that are the relations among saturation, capillary suction head and relative permeability, must be properly evaluated for calculating the saturated-unsaturated groundwater flow in rock mass. However, the practical technique for evaluating the properties has been lacked because the measurements of capillary suction and small rate of flow seeping through the unsaturated rock are much difficult. The present authors newly propose a back analytical technique for evaluating the hydraulic properties.<BR>A columnar rock specimen is prepared. The side of this specimen is completely sealed to avoid the evaporation from this side. The constant hydraulic head condition is given on the bottom of the specimen. When the air over the upper surface of the specimen is dry, water flows upwardly from the bottom through the specimen and evaporates at the upper surface. The evaporation rate is measured using evaporation sensor. The evaporation rate is the boundary flux condition of the flow through the specimen. After when the evaporation rate reaches the constant value, the specimen is broken and the vertical saturation distribution is measured. The saturation distribution can be calculated by solving the basic equation of one dimensional flow when the hydraulic properties of the specimen were given, because the boundary conditions are known. The hydraulic properties are back analytically looked for with many trial calculations. The van-Genuchten model is adapted for representing the properties and Maquet technique is used in this back analytical calculations.<BR>The hydraulic properties of two granitic rock and three Tertiary mud stone specimen were successfully measured. Transient moisture change in the mud stone, that was observed below an actual cutface, was also well analysed using the hydraulic properties evaluated by this technique.

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