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ニジゲン シントウ ハカイ ジッケン ニオケル ジッケン ジバン ノ トウスイ ケイスウ ギャクカイセキ

Inverse Analysis of Soil Permeability in Two-Dimensional Seepage Failure Tests

Japanese (日本語)

神戸大学都市安全研究センター研究報告

9

273-286

神戸大学都市安全研究センター

2005-03

2007-04-23

Two-dimensional seepage failure tests were conducted to throw light on the seepage failure mechanism of soil in front of a sheet pile wall. The seepage failure phenomenon is largely influenced by anisotropy of soil permeability. Therefore, the anisotropic permeability or coefficients of permeability tensor should be examined for test soils. In this study, methods of obtaining permeability tensor for two-dimensional test soils are discussed. The visual-estimation method is first applied and it is concluded that: (1) There is an anisotropy in permeability for test soils, i.e. permeability in the horizontal direction kxx is larger than that in the vertical kzz. The cross component of permeability tensor is expressed as kxz= O.O.　 The inverse analysis method was next applied using all of the measurements of hydraulic heads in test soil. And we have (2) Anisotropic permeabilities kxx/kzz obtained by visual-estimation and FEM-inverse-analysis are the same for some test soils, but are different for others. The difference is thought to be due to observation error. Here we consider the following four methods for dealing with residual δ with respect to hydraulic heads H's obtained by measurements and FEM analyses, where H is the hydraulic head difference between up- and downstream sides of sheet piles: i) The δ0 method based on an absolute value, in which we consider only data for ｜δ｜＜δ0. ii) Theβmethod based on a fraction of hydraulic head difference H, in which we consider only data for ｜δ｜＜βH. iii) The αmethod (Masuyama's method) in which defective samples are neglected based on t-test on the level of significance α%. iv) The γ method in which inverse matrix of standard errors σ is taken as weights w for measurements: w=(i/γ)2 for ｜σ｜<γσ0 and w=(σ0/σ)2 for ｜σ｜≧γσ0, where σ is the standard error for the weight w=1, residual δ is here taken as σ for each measurement. Here we can conclude that δ0=1.5mm,β=0.005, α =5% and γ=0.5 are recommended values for the above methods. Anisotropic permeabilities for test soils should be judged from visual-estimation and FEM-inverse-analysis.

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