現地橋梁沉箱基礎側推試驗之三維有限元素分析

本研究利用國家地震工程研究中心於宜蘭縣舊牛鬥橋所進行之現地大地試驗及橋梁沉箱基礎側推試驗，發展適用於卵礫石地層之沉箱基礎三維有限元素數值分析模式。此數值分析模式結合多孔介質彈性模型及Modified Drucker-Prager/Cap降伏模型予以模擬礫石層，透過現地大地試驗曲線來率定分析參數。本研究主要分為兩部分。第一部分先利用有限元素分析程式ABAQUS建立垂直及水平平鈑載重試驗之數值分析模型，以現地大地試驗結果配合現地平鈑載重試驗進行模擬，驗證分析模式之適用性，並率定分析參數。第二部分採用第一部分所建立之地層材料組成模式，建立沉箱基礎的數值分析模型進行模擬橋柱及基礎側推試驗，探討沉箱基礎受側向荷載時之行為，分析結果顯示，所採用之分析模型可有效模擬沉箱基礎在側向載重作用下之反應，包括橋柱頂部及基礎頂部之側向位移與轉角、土層於各深度之變位等。透過模擬不同荷載條件及基礎條件下之基礎側向荷載行為可知，基礎之側向荷載行為除受到上部結構物及載重型式之影響，亦會受到基礎裸露深度之影響，即基礎之荷載條件及裸露深度顯著地影響沉箱基礎之勁度與強度。

關鍵字

有限元素法；礫石層；平鈑載重試驗；沉箱基礎；側向荷載

並列摘要

This study simulates in situ lateral load tests on caisson-type bridge foundations conducted in Ilan County, Taiwan using three-dimensional finite element analysis. The test site was located on soil with high gravel content. The soil model used in the numerical model combines the Porous elastic model with the Modified Drucker-Prager/Cap model. The parameters of the soil model are calibrated using the results of plate loading testing. The study is divided into two parts. The first part is to verify the applicability of the soil model and determine the analysis parameters through simulation of the plate loading testing. The second part adopts the soil model calibrated from the first part and establishes the numerical analysis model of the caisson foundations to simulate the bridge column and foundation lateral load tests. The responses of the test caisson analyzed are in agreement with the measured, including the pier-head displacement and rotation, caisson displacement, caisson-head rotation, and soil displacement at different depths. In addition, according to the analysis results, load conditions and the exposed depth significantly affect the stiffness and the strength of the caisson foundations.