00406484

open access

Version of Record

ノウギョウヨウ カンセン スイロ コウジ ニオケル ボイリング ハッセイ ジレイ ト カイセキ

A case history and analysis of boiling during excavation in main canal works for agricultural use

Japanese (日本語)

神戸大学都市安全研究センター研究報告

7

181-193

神戸大学都市安全研究センター

2003-03

2007-04-17

Boiling occurred in the excavation bottom within double sheet piles in the North Main Canal Works in the Yoshino River Downstream Integrated Agricultural Land Disaster Prevention Project. A case history and countermeasures were described. Seepage flow (by FEM) and stability against seepage failure were analyzed. Characteristics of seepage flow and causes of the failure were discussed, and the following results were then obtained: (1) A permeable sand layer was overlaid with a less permeable silty sand layer, and a large head loss took place dominantly in the upper silty sand layer, and as a result seepage force was exerted downward on soil particles. (2) Soil was laid at both longitudinal ends to take the role of a loaded filter. It is speculated that boiling did not occur due to three-dimensional concentration of seepage flow into the corner of the excavation. (3) Seepage flow was concentrated into soil between the double sheet pile walls in two dimensions, and the safety factor against seepage failure of soil within the walls decreased drastically to one third of the safety factor of soil in front of a single sheet pile wall (an assumed condition). (4) The safety factors against seepage failure calculated using the Prismatic failure concept showed the same values with or without consideration of friction. This is because the upward seepage flow through soil surrounded by the double sheet pile walls was in a one-dimensional state, no effective stress remained in its critical state and no frictional resistances were exerted. (5) Especially where b/D is small, the safety factor for seepage failure decreases excessively. b is half the width between double sheet pile walls and D is the penetration depth of the walls on the excavation side. In the cases treated here, b/D=0.426 (at No.228+5m) and b/D=0.464 (at No.227). (6) It seems reasonable that the elevation of Ground Water Level (G.W.L.) at No.228+5m is equal to that of G.W.L. at No 227 located 105m away from the point No.228+5m.

浸透破壊に対する安定性

紀要論文