00200527

open access

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シントウ ハカイ モンダイ ニオケル ジバン ノ タソウケイ キンジ セイド

Accuracy of Approximation of a Gradually Varied-Permeability Ground to a Multi-Layered Syatem in Seepage-Failure Problem

Japanese (日本語)

神戸大学農学部研究報告

19(2)

125-133

神戸大学農学部

1991-01

2006-09-15

本文ファイルは、国立情報学研究所CiNiiより提供されたものです。

The accuracy of approximation of a gradually varied-permeability ground to a multi-layered system is discussed using the Critical State Calculation Program : CRIT 1. In this study, the multi-layers approximation of the hyperbolically varied-permeability ground with no loaded filter is investigated precisely, which is analysed theoretically in the previous paper. The following results are then obtained : (1) The equivalent Darcy's coefficient of permeability k_<av> is calculated accurately for every value of k_r by the multi-layers approximation. This is considered to be due to using Eq. (4) in calculating k_j. Where k_r is the ratio of the Darcy's coefficient of permeability of the top to one of the bottom of the ground, and k_j is the Darcy's coefficient of permeability of the j th stratum from the bottom layer. (2) For 0.0<k_r<1.0,in which the ground becomes critical at its top in the critical state, the accuracy of the multi-layers approximation is as follows : (i) Critical hydraulic head difference h_c : When the ground is divided into more than 50 layers, the calculation error of h_c can be lowered to less than 1%. (ii) Minimum effective overburden pressure of a loaded filter p_<1c min> : The calculation error of p_<1c min> is very large. Particularly, for 0.0<k_r<0.05,the ground must be divided into more than 1000 layers in order to reduce the calculation error of p_<1c min> to less than 1%. (iii) Area of the residual vertical effective normal stress diagram S_<res.> : When the ground is approximated to more than 149 layers or 289 layers, the calculation error of S_<res.> can be lowered to less than 1% or 0.5%, respectively. (iv) Location of the critical point z_t : When the ground is approximated to more than 100 layers, the calculation error of z_t can be lowered to less than 1%. (3) For k_r>1.0,in which the ground is critical at its bottom in the critical state, the accuracy of the multi-layers approximation is as follows : (i) h_c, p_<1c min> and z_t are calculated accurately by the multi-layers approximation. (ii) The calculation error of S_<res.> is very small. When the ground is approximated to more than 10&acd;11 layers, 31&acd;32 layers or 100 layers, the calculation errors of S_<res.> can be lowered to less than 1%, 0.1% or 0.01%, respectively. In this study, the only hyperbolically varied-permeability ground was discussed. It is, however, considered that the similar things are said for another-type gradually varied-permeability ground. An inverted filter is designed to be more permeable from the bottom to the upper part. In this case, particularly, the approximation accuracy of the filter to a multi-layered system is very high, which demonstrates the usefulness of the approximation method used here in designing the stability of the filter.

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