隧道開挖對節理岩體滲流行為影響之研究

Variation of Jointed Rock Permeability Induced by Tunnel Excavation

楊卓翰(Chou-Han Yang)

指導教授 ： 黃燦輝

共同指導教授 ： 王泰典

國立臺灣大學/工學院/土木工程學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.02007

摘要

在各種的地下開挖工程中，經常會遭遇到地下水的問題，尤其是開挖湧水的
案例更是層出不窮。岩體之應力場及滲流場往往為主導岩體工程安、穩定之關鍵，
故本研究擬建立岩體水力—力學耦合行為之分析模式，用以分析節理岩體受隧道
開挖擾動後之滲透係數變化。
本研究透過隧道開挖數值模型，及楊宗勳(2010)所提離散裂隙網絡模式(DFN)，
探討隧道開挖後圍岩滲透係數之變化。經由選取不同觀測範圍大小之岩體，對其
滲透係數進行統計以推求代表性體積元素RVE 大小，對其取多條測線求平均RQD
值，依據RMR 岩體分類法估計節理岩體之力學參數，藉此建立隧道之滲流模型。
為考量隧道開挖應力平衡過程其間水力與應力之互制行為以達到雙向耦合之目的，
本研究採分階疊代計算之方式，經由不斷疊代運算直到滲透係數值達穩定，即為
開挖擾動後之岩體滲透係數。
研究結果顯示：節理面剪脹量考量與否對滲透係數大小之影響相當顯著。節
理面與隧道開挖面相切時，隧道開挖徑向解壓而切向加壓的特性使節理面正向應
力降低而剪應力較大，剪脹量提供之內寬貢獻造成在開挖前後隧道面附近岩體滲
透係數相差達百倍。節理位態及側向岩壓係數的不同，對隧道開挖後圍岩之滲透
係數分佈具影響性。以側向岩壓係數0.5 為例，節理交角30 度時，於隧道頂拱及
仰拱處因隧道開挖切向加壓之力學特性滲透係數較低，側壁則由於軸向解壓緣故
滲透係數較高；當節理交角逐漸擴大，受壓區域不再為頂拱及仰拱，節理交角為
90 度時，其滲透係數較低之區域於隧道之兩側壁處，較大滲透係數之區域位於頂
拱及仰拱。以節理交角90 度為例，側向岩壓係數為0.5 時，隧道開挖後頂拱及仰
拱向內變形之趨勢較大，造成頂拱及仰拱處滲透係數較大。側向岩壓係數為1.5時，
隧道開挖後轉為兩側壁向內變形之趨勢明顯，頂拱及仰拱處切向加壓劇烈，使滲
透係數在頂拱及仰拱較低，兩側壁則因向內變形的緣故節理面正向應力相對較低，
使滲透係數在兩側壁較大。側向岩壓係數等於1 的狀況下，因為應力為均向的緣
故，在隧道開挖後隧道均勻向內變形，導致滲透係數之擾動區域最小。

關鍵字

節理岩體 ； 水力耦合 ； 隧道 ； 離散裂隙網絡 ； 代表性體積元素 RVE

並列摘要

In various underground excavations, groundwater issue is an often encountered problem, among which massive water inflow is frequently reported. The deductions of flow field and mechanical field of fractured rock mass are always the key to safe rock engineering. In this study, a coupled hydro-mechanical analysis procedure is proposed and used to probe into the variation of hydraulic conductivity of jointed rock mass induced by tunnel excavation.
In this study, a numerical model of tunnel excavation and the discrete fractured networks (DFN) proposed by Zong-Xun Yang (2010) is used to explore the changes of jointed rock mass hydraulic conductivity after tunnel excavation. Through selecting different observation ranges of the rock mass and evaluating statistics of the hydraulic conductivity, we deduce the size of representative volume element (RVE). Scan line method is used to compute the average RQD value of the RVE. According to RMR
classification, the mechanical parameters of the jointed rock mass is estimated, and a
numerical tunnel seepage model is created. The iterative computing method is proposed
in this study to consider the coupling hydro-mechanical effect during the stress
equilibrium process though tunnel excavation. The iterative computation stops until the
hydraulic conductivity stabilized, that is, the hydraulic conductivity of the jointed rock
mass after disturbance.
Results of numerical simulation indicate that the joint dilation has a significant
impact on the jointed rock mass hydraulic conductivity. On the joint plane which is
tangential to the tunnel wall, the normal stress on joint plane decreases and shear stress
increases. Such behavior causes the hydraulic conductivity around tunnel surface surge
a hundred times larger than its initial value. It is also found that the joint dilation would
III
influence the jointed rock mass hydraulic conductivity remarkably. Different joint dip
angles and the coefficient of lateral earth pressure cause different distribution of jointed
rock hydraulic conductivity as well. Taking the coefficient of lateral earth pressure 0.5
for example, when joint cross angle equals to 30 degree, the hydraulic conductivity of
the jointed rock mass is low at tunnel roof and floor; on the contrary, it is high at tunnel
sidewalls. This distribution is caused by the effect of tunnel excavation, during which
the stress tends to decrease in radial direction and increase in tangential direction. As the
included angle of joints increases, the distribution of hydraulic conductivity changes too.
When the included angle of joints equals to 90 degree, the permeability of the jointed
rock mass falls at tunnel sidewall, and rises at tunnel roof and floor. As to the two cases
with lateral earth pressure coefficients 0.5 and 1.5, the rock mass deformation in the
former one concentrate on roof and floor of the tunnel, while it localizes at sidewalls in
the later one, causing subsequent increase in coefficient of hydraulic conductivity within
these areas. For cases with lateral earth pressure equals to 1.0, the stress distribution and
deformation is uniform, thus the variation of rock mass hydraulic conductivity is the least of the three.

並列關鍵字

jointed rock mass ； hydro-mechanical coupling ； tunnel ； discrete fractured networks (DFN) ； representative volume element (RVE)

參考文獻

1. 江誌偉(2008)，“裂隙岩體滲流離散模式之研究”，國立台灣大學土木工程學研

7. 楊宗勳(2010)，“裂隙岩體滲流參數影響之研究”，國立台灣大學土木工程學研

3. 林宏奕(2002)，“破裂岩體隧道開挖對滲透係數之影響—以雪山隧道為例”，國

9. 鄭允嘉(2006) “節理岩體滲透係數之先天異向性與應力引致異向性”，國立中央

10. Bandis, S., A. C. Lumsden and N. R. Barton (1983), “Fundamentals of rock joint