液化土壤模數折減下樁基動力反應分析

Analyses for Dynamic Responses of Pile Foundations Affected by Modulus Reduction of Liquefied Soils

巫秀星(Sho-Sing Wu)

指導教授 ： 張德文

淡江大學/工學院/土木工程學系碩士班/碩士(2005年)

https://doi.org/10.6846/TKU.2005.00400

摘要

本研究係以波動方程模擬地盤液化狀態下樁基礎之動態反應，依據現場土層鑽探資料與測站地震紀錄，藉日本相關規範之土壤液化評估法分析其土質折減係數，並將此折減係數施用於土壤模數值，配合集中質塊分析模擬自由場地盤液化反應，再將地盤反應作用於樁之波動方程解，用以說明液化地盤內樁基之變形行為與破壞機制。研究除以員林地區地質構造特性討論相關分析外，並以日本新瀉地震之數項破壞案例驗證本研究之合理性。
研究發現：（1）液化下之土質折減係數分析將不致改變近地表之最大地盤位移和樁體變形量，但將使液化區土層的位移和樁體的變形和彎矩放大，衍生破壞。（2）無論土壤液化與否，大型地震將致使樁基頂部產生過量彎矩和剪力，造成混凝土開裂，進一步產生彎矩破壞並致使樁基被剪斷。（3）經研究發現液化土層中樁基結構系統之破壞模式將以複合型態發生，其並與樁頂束制條件有關；而非液化與液化土層之交界處應注意樁基礎之結構設計（4）本研究建立之簡易分析模式，可涵蓋土層液化時之弱化現象，且能有效掌控地盤反應與樁基礎間互制行為，將有助於預測液化中樁基礎引發之破壞行為。

關鍵字

波動方程分析 ； 樁基 ； 液化 ； 土質折減係數 ； 破壞

並列摘要

In this study, wave equation is used to model the dynamic responses of the foundation in a liquefied ground due to the earthquake. Based on the bore-hole data and the seismic records, the soil parameter reduction factor can be obtained from the liquefaction potential analysis such as those suggested in the Japanese codes. The reduction factor can be used to reduce the soil stiffness along the pile in the liquefaction zone. Lumped mass analysis is performed to obtain the free-field response of the liquefied ground. The deformations of the ground are then superimposed onto the pile elements for the discrete wave equation analysis. Thus the pile response and the failure mechanism are investigated. Besides the studies on Yuan-Lin County sites with Chi-Chi earthquake record, a number of case studies for 1964 Niigata earthquake are used to validate the proposed procedures.
The main observations of this study are: (1) The ground displacements at the surface would not be amplified by the soil liquefactions, however the ground and the pile displacements are significantly increased in the zone of liquefaction. (2) With or without the liquefaction, a large earthquake would cause excessive moments and shears for the piles near to the head, in which the pile may fail accordingly. (3) Complex failure mechanism could happen according to the connections between the pile and the cap. Further cautions would be required for the foundation structure near by the interfaces of the liquefied and non-liquefied soil layers. (4) The procedures suggested in this study could predict successfully the pile foundation responses in a liquefied ground. It can be used to model effectively for the failure behavior of the pile foundation due to the soil liquefaction.

並列關鍵字

Wave equation analysis ； pile foundation ； liquefaction ； soil reduction parameters ； failure

參考文獻

33. 黃俊鴻、陳正興（1998），“土壤液化評估規範之回顧與前瞻”地工技術，第70期，第23-44頁。

34. 翁作新、陳正興、黃俊鴻（2004），“國內土壤受震液化問題之檢討” 地工技術，第100期，第63-78頁。

44. 張德文，林伯勳 (2003)，“含樁帽及互制影響之波動方程分析”，地工技術雜誌，第九十五期，第49-60頁。

2. Chang, D. W. and Yeh, S. H. (1999), “Time-Domain Wave Equation analysis of single Piles Utilizing Transformed Radiation Damping”, Soils and foundations, JGS. , Vol. 39, No. 2, pp. 31-44.

3. Chang, D. W., Roesset, J .M. and Wen, C. H. (2000), “A Time-Domain Viscous Damping Model Based on Frequency-Depend Damping Ratios”, Soil Dynamic and Earthquake Engineering, Vol. 19, pp. 551-558.