國內慣用之開挖底部隆起分析法的土壤強度異向性考慮

Effect of Strength Anisotropy on Current Design Method for Base Stability of Deep Excavation in Clay

廖洪鈞(H. J. Liao) ； 蘇世豐(S. F. Su)

《地工技術》 76期 (1999/12) Pp. 63-74

https://doi.org/10.30140/SG.199912.0004

摘要

本文從土壤強度異向性的觀點，探討國內慣用之開挖底部隆起分析法（亦即是中華民國大地工程學會1998年版「建築技術規則建築構造編基礎構造設計規範」之建議方法），其有關土壤不排水剪力強度的選用問題。就該分析法所建議之破壞機制而言，沿著破壞面上各點土壤元素，其最大主應力方向均不相同，顯示土壤強度異向性對現行分析法有其影響性。有鑑於此，本文乃結合適用於異向性軟弱粘土之不排水剪力強度準則和國內慣用分析法之隆起分析機制，提出一套可以考慮土壤強度異向性之開挖底部隆起分析法，並以美國波士頓之數值模擬案例和台北市之隆起破壞案例來印證其可行性。最後將建議之異向性分析法的結果與目前慣用之等向性分析法的結果加以比較，定出在不同開挖條件下（諸如開挖幾何關係是寬而淺或是窄而深），目前慣用分析法的適用範圍，以供設計者之參考。

關鍵字

深開挖 ； 隆起分析 ； 粘土 ； 強度異向性

並列摘要

This paper is to evaluate the effect of strength anisotropy on the current design method on the base stability of deep excavation in clay. Basically, the current method is an isotropic strength method and does not consider the effect of strength anisotropy. However, the direction of major principal stress changes along the slip surface beneath the base of excavation. To evaluate the effects of soil strength anisotropy on the calculated factor of safety against basal heave, an anisotropic strength criterion for soft clay is adopted here. After combining this strength criterion with the failure mechanism of the current design method, a modified method for analyzing the base stability of excavation can be established. The suitability of the proposed method has been verified by comparing with the numerical study results of deep excavations in Boston and a base failure case in Taipei. Finally, the results obtained from the proposed anisotropic strength method and the current isotropic strength method are compared. The range where the strength anisotropy of clay has little effect on the result calculated from the isotropic strength method under vavious construction conditions are identified also.

並列關鍵字

deep excavation ； basal heave analysis ； clay ； strength anisotropy