A Study of Vertical Earthquake Effect on Stability Behavior of Retaining Wall

臺灣地震頻繁，特別是921集集大地震後，國內對於結構物的耐震設計之考量更加慎重，而土壤結構物受地震作用下之結構設計，其水平地震係數採一般建築結構物之1/2，而垂直地震係數一般則採水平地震係數值之1/2，惟地震作用下垂直效應進一步之探討，似乎較為缺乏，因此針對現有一些擋土牆受地震作用力之評估方式有深入研究之必要。 本文進行垂直地震效應對擋土牆穩定性影響之研究，針對兩類型重力式擋土牆四個研究範例，利用工程計算方法與PCSTABL程式，探討擋土牆之穩定性與相關力學行為，工程計算方法結果顯示：(1) 牆背前傾之擋土牆，不論常時或地震情況下，其抗傾覆與抗滑動之安全係數均較牆背為垂直之擋土牆為低；(2) 垂直地震係數增加，抗傾覆與抗滑動之安全係數不減少反而增加，但其增加幅度不大；(3) 牆背前傾之擋土牆，不論常時或地震情況下，其底版承受最大土壓力數值較牆背為垂直之擋土牆為高。PCSTABL程式分析結果顯示：(4) 抗滑動安全係數，以PCSTABL程式分析結果較工程計算方法有較低數值，因前者係選擇較為臨界之可能滑動面；(5) 受地震作用下整體滑動之安全係數較常時為低，惟垂直地震係數之改變，對於整體滑動安全係數之影響極為有限。Earthquake occurs frequently in Taiwan area. More considerations are in the earthquake-resistant design of internal structures especially after the 921 Chi-Chi earthquake. The design of earth structures under seismic motion is based on the fact that the horizontal seismic coefficient is half that of general building, while the vertical effect is considered as only half of horizontal seismic coefficient. However, the vertical effect under seismic motion is short of further study. Therefore, the evaluation of retaining walls under seismic motion is worthwhile more research. This paper studies the stability effect of retaining walls under vertically seismic motion with two types of gravity retaining walls and four research examples. The engineering computation method and PCSTABL program are used to study the stability and related mechanical behavior of retaining walls. From the analyzed results of engineering computation method, it indicates that (1).The safety factors of resistance in overturning and sliding for retaining wall with back wall leaning forwards are less than those for back wall vertically, no matter what it is under normal or earthquake condition; (2).The safety factors of resistance in overturning and sliding for retaining wall increase with increasing vertical seismic coefficients, but the amplitude is little; (3).The maximum soil pressures beneath the wall bottom slab of retaining wall with back wall leaning forwards are greater than those of retaining wall with back wall vertically. On the other hand, from the analyzed results of PCSTABL program, it shows that (4). The safety factors of resistance in sliding using PCSTABL program are less than those by engineering computation method. This is attributed that the former traces the more critical sliding surfaces; (5). The safety factors of resistance in global sliding under seismic motion are less than those under normal condition, while the little effect is found with the variation of vertical seismic coefficients.致謝 i 中文摘要 ii ABSTRACT iii 目錄 iv 圖目錄 vii 表目錄 x 符號表 xi 第一章 緒論 1 1.1 前言 1 1.2 研究動機與目的 2 1.3 研究方法與流程 2 1.4 研究內容 3 第二章 文獻回顧 4 2.1 側向土壓力 4 2.2 Rankine側向土壓力理論 7 2.3 Coulomb側向土壓力理論 11 2.4 擋土構造之設計 13 2.5 擋土牆牆體穩定性 21 2.6 擋土牆的設計步驟 28 2.7 Mononobe-Okabe 動態土壓力 30 2.8 其他相關研究 33 第三章 PCSTABL程式簡介 35 3.1 前言 35 3.2 分析原理與方法 35 3.3 分析方法與適用條件 36 3.4 PCSTABL6 程式分析邊坡穩定流程 36 3.5 程式指令 39 3.6 PCSTABL6 程式應用特色 40 第四章 研究範例工程設計分析 41 4.1 研究範例一 41 4.2 研究範例二 57 4.3 研究範例三 69 4.4 研究範例四 80 4.5 研究範例之綜合比較分析 91 第五章 研究範例PCSTABL程式分析 97 5.1 研究範例 97 5.2 分析結果之檢討 97 第六章 結論與建議 104 6.1 結論 104 6.2 建議 105 參考文獻 10