液化地盤之群樁行為研究

Seismic Behaviors of Group Piles in Liquefied Soils

林佑軒(You-Syuan Lin)

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(2017年)

https://doi.org/10.6846/TKU.2017.00217

摘要

本研究係採用 EQWEAP (EarthQuake Wave Equation Analysis for Piles)一維波動方程式分析群樁基礎行為，並進行液化地盤下的基礎行為分析。透過不同地震加速度歷時紀錄進行動力分析，以了解不同地震歷時紀錄下該項分析的適用性。研究首先將重點置於土壤液化模式的驗證之上，以其他學者的實驗數據了解本研究所選用的模式參數影響，再進行自由場地盤反應分析，了解不同地震影響；再以單樁和群樁基礎進行分析，了解不同分析的可能差別。以地盤液化對樁基礎影響為研究重點，本研究係採用集中質塊法、波動方程式所開發的EQWEAP 做為模擬基礎底層土壤-樁基承受地震力之工具，土壤模式選用為模擬動態地震力和土壤液化行為所需考慮之問題，自由場採用Byrne(2004)所建議之UBCSAND model 模擬飽和砂土在地震力下所產生的超額孔隙水壓激發，再配合知名地震記錄，模擬單一均質的土壤行為，並以三維有限元素動力分析 Midas GTS NX 軟體做為比較工具，採用2016年版新增之土壤組成律Modified UBCSAND model (Byrne, 1998)進行非線性動力分析模擬群樁基礎。
研究結果顯示: 1. UBCSAND model(Byrne, 2004)可做為砂土材料，液化行為經與實驗室數據比較證明其可行性。2. 根據不同地震對自由場的模擬，研究發現地震歷時函數將為地盤反應關鍵參數。加速度傅氏譜卓越週期或累積振幅量愈大者地盤反應愈明顯，且會造成較大的永久變位。3. 採用簡易一維集中質塊分析配合Byrne (2004)模式可掌握地盤的液化行為(位移、應力和應變等)，其結果在位移上與三維有限元素分析結果差異不大。4. 採用EQWEAP分析可模擬群樁基礎受震反應，各樁的分配力對基樁受震反應影響不明顯；同時，單樁的受震反應將取決於地盤運動，不隨樁數增加、樁長變化而產生較大的影響。5. EQWEAP分析無法模擬地盤對樁身所造成的永久位移影響，但其內力和扣除永久變位後的有限元素分析所得結果相似；且非線性基樁和線性基樁分析差異不大，顯示使用線性基樁分析在實務上的合理性。

關鍵字

群樁基礎 ； 液化模式 ； 波動方程 ； 動力分析 ； 三維有限元素分析

並列摘要

This study intends to discuss the seismic behaviors of group piles with the one- dimensional wave-equation modeling EQWEAP (EarthQuake Wave Equation Analysis for Piles) in liquefied soils through different seismic acceleration records. The suitability of EQWEAP applies in liquefied soils is investigated. First of all, the research focuses on the validation of soil liquefaction model, supported by the experimental data from other scholars to validate the UBCSAND model (Byrne, 2004). Moreover, the implementation of free field reaction analysis is to understand the impact of different earthquakes and their influences on single pile and grouped piles. By applying the UBCSAND model to obtain the solution of EQWEAP, the seismic free-field response of the site was computed from the lumped mass analysis and excess pore water pressure model; the soil deformations were imposed onto the pile foundation to conduct the wave equation analysis. One-dimensional EQWEAP analysis is compared to three-dimensional finite element analysis program MIDAS GTS NX to ensure the reliability of the EQWEAP analysis in the applications.
The results are summarized as follows: (1) The solutions from UBCSAND model at material level were found similar to experimental data shown by other scholars on cyclic simple shear and dynamic triaxial tests. (2) According to the simulation of the free field on different earthquakes, it is found that the key point is the ground response. The greater predominant period and larger accumulated Fourier amplitudes of the acceleration at 0-100 Hz will create larger responses of the site, and it will cause greater permanent displacements. (3) By comparing EQWEAP analysis with MIDAS GTS NX analysis on piles, the results were found compatible. (4) It is found that the responses of grouped piles are very similar to each other. The changes of water level, SPT-N value, and pile length caused minor effects to the displacements and internal stresses of the piles. (5) EQWEAP analysis does not simulate the permanent displacement, but the internal stresses found are similar to the finite element analysis after the deduction of permanent displacements. In addition, the difference between nonlinear pile and linear pile is not distinctive.

並列關鍵字

Group Pile Foundation ； Liquefaction Model ； Wave Equation Analysis ； Dynamic Analysis ； Three-dimensional Finite Element Analysis

參考文獻

3. 王彥誌 (2012)，「以波動方程和有限元素分析樁基礎受震行為之比較」，碩士論文，淡江大學土木工程研究所，台灣，淡水。

4. 王寅綸 (2013)，「樁基礎耐震性能之研究」，碩士論文，淡江大學土木工程研究所，台灣，淡水。

11. 宋士豪 (2012)，「樁基承載力與耐震性能之關聯性研究」，碩士論文，淡江大學土木工程研究所，台灣，淡水。

14. 林煒宸 (2014)，「樁筏基礎受力變形之有限元素分析」，碩士論文，淡江大學土木工程研究所，台灣，淡水。

19. 張紹綸 (2008)，“孔隙水壓模式應用於液化影響樁基礎之波動方程分析”，碩士論文，淡江大學土木工程研究所，台灣，淡水。