不連續面先天異向性及應力異向性對開挖圍岩滲透特性之影響;Inherent and stress-induced anisotropy of hydraulic conductivity around a rock tunnel - equivalent continuum approach

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题名:	不連續面先天異向性及應力異向性對開挖圍岩滲透特性之影響;Inherent and stress-induced anisotropy of hydraulic conductivity around a rock tunnel - equivalent continuum approach
作者:	賴柏松;Lai, Po-Sung
贡献者:	應用地質研究所
关键词:	隧道開挖;應力重新分布;先天異向性;應力異向性;水力傳導係數;流場;滲流量
日期:	2017-07-28
上传时间:	2017-10-27 16:18:19 (UTC+8)
出版者:	國立中央大學
摘要:	舉凡山岳隧道工程與放射性廢棄物處置等議題，地下水於壁面圍岩之流動行為及出水量常為工程成敗之關鍵。岩盤隧道開挖過程中，壁面之應力狀態將重新分布進而改變滲透特性，且隧道周圍流場亦將受到滲透特性與開挖面壓力水頭為零之影響，因此本研究探討隧道開挖導致滲透特性與流場之變化。前人研究發現不連續面位態分布會使裂隙岩體水力傳導係數產生先天異向性(inherent anisotropy)，同時應力會影響不連續面之開口寬，亦將導致水力傳導係數產生應力引致異向性(stress induced anisotropy)，基於此兩者特性及影響，利用隧道開挖過程產生的應力重新分布之影響為例，採用擬連續概念建立之Oda模式，加入了JRC-JCS模式計算隧道壁面附近不連續面開口寬隨正向應力與剪應力改變之水力傳導係數張量，此一水力傳導係數張量為裂隙岩體所受應力狀態影響之函數。成果顯示，隧道開挖應力重新分布造成之應力異向性將造成隧道周圍岩盤最大水力傳導係數主值增加約2個數量級，並造成水力傳導係數之異向性增加，主方向亦有顯著變化，若忽略不連續面剪脹行為，將過份低估隧道周圍岩盤之水力傳導係數；然而邊界(大地)應力異向性對水力傳導係數之影響相對隧道開挖後應力重新分布之影響較小。不連續面先天異向性及邊界應力異向性亦將影響水力傳導係數主方向，且造成隧道側壁與頂拱滲透特性不同。隨著平均岩覆應力增加，隧道開挖後應力重新分布對岩盤水力傳導係數主值之影響降低，且影響範圍亦變小，然而對水力傳導係數主方向之影響較不明顯。隧道周圍流場亦同時受到隧道開挖應力重新分布、不連續面先天異向性以及邊界應力異向性影響，造成隧道頂拱與側壁之滲流量不同，然而不考慮剪脹對於隧道滲流量之影響並不顯著。;The hydraulic conductivity around the tunnel is one of the key parameters for the safety assessment of radioactive waste disposal and mountain tunnel engineering. This study aims to explore the inherent anisotropy (orientation of the discontinuities) and stress induced anisotropy of the hydraulic conductivity around a rock tunnel. JRC-JCS model is used to estimate the aperture of discontinuities under stress, and consider the shear dilatancy effect of discontinuities at the same time. Based on the calculated stress field via Kirsch solution (1898) and the equivalent continuum model, the hydraulic conductivities around a circular tunnel can be calculated. The groundwater inflow of the tunnel is further evaluated via finite difference method. The result shows that the hydraulic conductivity on the tunnel wall is about 1 ~ 2 orders of magnitude larger than the one away from the tunnel (or the one of rock mass under boundary stress). If the shear dilatancy effect does not be considered, the hydraulic conductivity will be underestimate (about 60 times with considering shear dilatancy effect condition) The major principal hydraulic conductivity on the tunnel wall can be 4 ~ 10 times larger than the minor principal value. The principle directions of the hydraulic conductivity near the tunnel wall are also significantly deviated from the tangential and radial directions when the inherent anisotropy is considered. In this study, boundary stress has less influence on hydraulic conductivity around the tunnel than stress redistribution caused by tunnel excavation. With increasing boundary stress the influence of tress redistribution on hydraulic conductivity around the tunnel will decrease. Groundwater flow analysis shows that the total head and the flow velocity are dominated by the inherent and stress induced anisotropy of hydraulic conductivity. Surprisingly, the inflow of the tunnel is insignificantly influenced by the spatial variation of hydraulic conductivity around the tunnel wall.
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