應用個別元素法模擬卵礫石層中管道開挖之行為

Modeling of Pipeline Excavation in Gravel Formation Using Distinct Element Method

林晉德(Ching-Te Lin)

指導教授 ： 徐松圻

朝陽科技大學/理工學院/營建工程系碩士在職專班/碩士(2011年)

摘要

由於卵礫石層為大小不同顆粒所組成之複合土層，其性質乃顆粒間之相互滑動、滾動及顆粒間之互鎖及粒徑大小分佈等所控制，應視為不連續體來分析模擬。卵礫石其力學行為主要與卵礫石顆粒形狀、大小、排列方式、細料含量及性質有密切的關係，而且粗、細顆粒含量之多寡對於卵礫石層之工程性質也有影響。
本研究主在，藉由改變不同的管道管徑、管頂覆土深及顆粒旋轉性情況，來探討土體之穩定性及破壞影響範圍，模擬分析開放式管道開挖在卵礫石層中之破壞機制，而數值模擬方法則採用個別元素法為主之數值程式 PFC2D，並觀察於不同階段時，顆粒滑動、滾動之位移影響情形。
由分析結果顯示，開挖面主要破壞由管道開口接近頂拱處先產生滑動及滾動崩塌，再逐步向管道錢及向上延伸崩塌，並可能導致地表下陷。當現地卵礫石愈趨近於圓形顆粒，開挖時極易崩塌，將來需採用先撐工法。由顆粒旋轉性對開挖面穩定模擬結果顯示，當卵礫石顆粒形狀愈趨向橢圓或微扁平狀時，即限制部分大顆粒之旋轉時，顆粒間排列之互鎖效應愈明顯，即便顆粒間填充較小的顆粒，開挖後仍具有極佳的自立性。顆粒旋轉度對管前影響分析顯示，相同管徑下，管前影響隨著深徑比增加而無太大變化。相同深徑比下，管前影響隨著管徑增加而增加。

關鍵字

個別元素法 ； 卵礫石 ； PFC ； 管道開挖

並列摘要

The gravel formation in Taichung consists of granular materials with various sizes and can be considered as a compound material. The properties of the formation are mainly determined by slipping, interlocking, and rolling between particles and grain size distribution. The gravel formation can be regarded as a discontinuous material for simulation and analysis. The mechanical behavior exhibited by the gravels is closely related to gravel size, gravel shape, size distribution, and percentage of fines content. The percentage of coarse and fine particles has a great impact on its engineering properties.
In order to study the failure mechanisms and failure zones of open-face underground pipe excavation, different diameters, overburdens, and rotation characteristics of the gravel are considered to simulate. Distinct element method based numerical software, PFC2D, is used to model the excavations. The displacements in front of the pipe due to slipping and rolling of the particles are observed and compared at certain time step.
The results obtained from the analysis allowing particles free to rotate showed that the failure of excavation face started near the crown (roof) and extended forward and upward. The failure zone may extend up to the ground surface. Therefore, if most of the granular materials have rounded shape, then the excavated face will be easily fall off and collapse, and the forepoling method should be required for excavation. However, the particle shape of the gravel at larger size is more like oval shape or slighted flattened and not rounded, thus, the rotation of the larger particles will be prohibited during moving. The interlocking effect is more prominent as the bigger particles are fixed, i.e. no rotation, only some particles close to the face fall off after excavation, especially if the particle sizes greater than D50 are fixed. Therefore, the excavated face can stand up pretty well as observed in situ open-type pipe excavation. If only the particles greater than D90 are fixed, the extended range in front of the pipe is about the same for the same diameter under different overburden, but the range increases as the diameter increases at the same overburden.

並列關鍵字

distinct element method ； PFC2D ； underground pipe excavation ； gravel

參考文獻

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