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標題: 台中地區卵礫石層管推進工程之研究
A Study of the Pipejacking Construction in the Gravel Formations in Taichung Area
作者: 林棕元
Yuan, Lin Tsung
關鍵字: gravel formations;卵礫石層;pipejacking;underground excavation;finite element method;管推進工程;地下開挖;有限元素法
出版社: 土木工程學系
新建或更新維生管線為都市發展必須面對的工作,傳統之明挖工法有施工簡易、造價低廉之優點,但其對環境及交通之衝擊大,或遭遇地表無法開挖的障礙時也不能採用,因此有非明挖之工法之發展與應用。台中地區之地層,除地表4m以內的表土層外,主要為渾厚之卵礫石層;且因卵礫石屬石英砂岩,質地相當堅硬,一般仍多以人工方式代替機械進行地下開挖施工。近年來台中都會區非明挖之管推進工法漸漸被採用,卵礫石層管推進工程之分析研究為急需探討之課題。本研究對台中地區於民國86至 88年間的管推進工程進行現地案例調查,共蒐集調查11個管推進工程進行案例調查,針對相關資料進行分析探討,並利用有限元素程式ABAQUS進行三維數值分析,模擬卵礫石層地下開挖之行為。
本研究參考前人研究之文獻資料,並根據現場試驗所得部分之參數,利用ABAQUS有限元素法程式進行管推進工程之三維模擬。考慮卵礫石土之應力-應變關係為彈性完全塑性( elasto perfectly plastic ),塑性部分主要採用Mohr-Coulomb塑性降伏準則模擬。分析管推進工程地下開挖過程卵礫石層受力及變形行為,所得之結果與現場觀測值比較,並探討不同內摩擦角f、管頂覆土深度(d)、靜止土壓力係數Ko、輪進長度(S)、管直徑(D)及前進面效應對開挖穩定之影響。

Constructing or renewing service pipelines is one of the major construction works during development of an urban area. Traditional trench excavating method has advantages, such as easy working and low cost, etc., however, it has large impact on not only the environment but also the traffic. Also, it does not suitable for the conditions with permanent surface facilities. Therefore, trenchless construction methods were developed and applied to avoid those difficulties. The surface formations of Taichung area, besides a 4 meter thick soil, consists of a gravel formations thicker than 50 meters. As the quartz-sandstone gravel is very hard and difficult to break, the most common excavation methods are non-mechanical and semi-mechanical methods. In recent years, due to the rapid development of the city, there are more and more trenchless pipejacking constructions. The objective of the this study is focused on the pipejacking construction in gravel formations. The study investigated and analyzed 11 pipejacking constructions in Taichung area during 1997~1999. Besides, the finite element software ABAQUS was used to simulate the behavior of underground excavation in the gravel formations.
In the three-dimensional pipejacking simulation, elasto perfectly plastic stress-strain relationship as well as the Mohr-Coulomb plasticity yielding model was used. We analyzed the behavior of the gravel formations in the process of pipejacking construction and compare the numerical results with the in-situ subsidence surveying results. A systematic analysis was also performed to investigate the influence of friction angle(f), overburden depth(d), earth pressure coefficient at rest(Ko), unsupported span(S), and pipe diameter(D) .
A pipejacking construction at the crossroad of the Sinhochung Road and the Chungching Road (overburden depth=3.7m, pipe diameter =2.6m, excavated length=32m) was chosen for the case study. Analysis results only shows qualitatively reasonable behavior, and as the typical case is in the extreme shallow tunnel category and lack of references, the special deformation behavior needs more advanced study. From the parameter study, it shows that the largest settlement increases as the overburden depth(d) increases. In addition, the surface heaving phenomenon becomes less significant as the overburden depth increases. When the earth pressure coefficient at rest(Ko) or friction angle(f) increases, the largest settlement becomes smaller. The largest settlement becomes larger as the unsupported span(S) or pipe diameter(D) increases .
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