臺北市深開挖受震行為之數值模擬

Numerical Investigation of Behavior of Deep Excavation in Taipei City Subjected to Seismic Ground Motion

蔡哲倫(Che-Lun Tsai)

指導教授 ： 郭安妮

國立臺灣大學/工學院/土木工程學研究所/碩士(2022年)

https://doi.org/10.6342/NTU202200797

摘要

由於深開挖工程在整個工程施作期間甚至建築結構之50年生命週期中僅占據非常短的時間，因此過去甚少有針對深開挖工程受震下之行為的研究文獻，然而現如今有越來越多長工期之深開挖工程，例如捷運系統之開挖工程往往花費數年，台灣由於位於環太平洋地震帶，各式大小的地震發生頻繁，其中臺北盆地由於具備盆地效應以及地層軟弱之特性，因此必須對於建築結構之抗震能力有特殊要求。本研究以有限元素差分數值模擬軟體FLAC 2D 7.0探討在台北盆地軟弱粉土質黏土下深開挖工程承受台北盆地475年回歸週期設計地震力下之行為，本研究首先以EGDT資料庫提供之台北各地區之剪力波速剖面建立地層之數值模型，接著以加州柏克萊大學建立的PEER Ground Motion Database找出7組反應譜與台北盆地475年回歸週期設計地震型態相近之地震歷時，再將這7組地震歷時分別乘上相對應的放大係數即可模擬台北盆地之設計地震，這七組地震歷時分別具備不同的主要頻率含量及強地動延時(D5-95)，並將地震歷時輸入深開挖之數值模型中進行分析。本研究使用了六種深開挖尺寸，包含了三種開挖深度及兩種水平支撐間距，以探討深開挖工程遭受475年設計地震時之壁體變位、剪力及彎矩分布、動態土壓、地表沈陷及開挖面隆起，其中由於目前建築物耐震設計規範建議以Mononobe-Okabe提出之公式設計動態土壓力，然而此公式適用於懸臂式擋土牆及無凝聚力土壤，對於使用支撐式擋土系統之軟弱黏土深開挖工程的適用性有待探討，因此本研究也將以此公式與數值模擬所得之動態土壓進行比較與分析。

關鍵字

深開挖 ； 有限元素差分 ； 設計地震力 ； M-O動態土壓力法

並列摘要

Taiwan is located in the Circum-Pacific Belt. There are more than 18000 earthquakes annually. Failures of basement or deep-excavation walls in earthquakes are rare even if the structures were not designed for the actual magnitude of the earthquake loading so there are only a limited number of studies focusing on the behavior of braced excavation under seismic conditions. However, we still need to develop a better understanding of the distribution and magnitude of the seismic earth pressures on braced retaining structures since nowadays many metro systems construction projects continue for several years, it is necessary that these underground retaining systems be designed for an earthquake condition, especially in high seismic density area such as Taiwan.
To understand the distribution of lateral earth pressure, moment, and displacement of diaphragm wall for deep excavation considering seismic condition, finite difference method (FDM) is used to simulate deep excavation construction with different geometry factors under several ground motions with a magnitude of 475 years design earthquake and different values of predominant period and significant duration. After finishing the FDM models, we will do the analysis to understand the effect of predominant frequency and significant duration and excavation size on behavior of braced excavation and then compare the simulated seismic pressure with that from Mononobe-Okabe.

並列關鍵字

deep excavation ； FDM ； design earthquake ； M-O method

參考文獻

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