等值節理岩體組成模式應用於隧道三維變形分析

Simulating Three Dimensional Deformation of Tunnels Using Equivalent Jointed Rock Masses Model

黃亮儒(Liang-Ju Huang)

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(2022年)

https://doi.org/10.6342/NTU202201796

摘要

隧道開挖過程中常會遇到抽坍與擠壓等工程災害，分析隧道穩定性時除了須考慮開挖對於隧道圍岩所造成的擾動外，隧道變形控制及圍岩降伏區域分布狀況亦為工程設計上所需要考慮的要點。以現代隧道工法的理念，由於現地應力、岩材性質及施工方法等複雜因素的影響，隧道圍岩受開挖擾動所引致的應力極可能使其達到強度值，圍岩達尖峰強度後將導致隧道周圍的變位明顯增加，大幅影響隧道淨空變形，且於某些條件下會產生擠壓破壞。
本研究考慮完整岩材力學特性、節理面力學特性與空間分布等影響岩體彈塑性變形行為之重要因素，採用前人研究所提出之節理岩體組成模式，依據等值連續體與代表性體積元素等概念建立一套三向度數值模式，經由室內節理岩體單軸壓縮試驗以及前人二維數值模擬結果的驗證後，用以分析隧道開挖過程中三維尺度下之變形與圍岩降伏情況。
節理岩體單軸壓縮的驗證，本文主要以楊長義(1992)所建立之節理岩體為模型設置對象，並給予相對應的參數條件進行模擬，並以王泰典(2003)理論模式之預測結果相驗證。隧道模擬部分，本文則先假設雙組節理正向勁度極高的情況進行模擬，並與Kirsch(1989)所提出的解析解相驗證；接著建置不同組數節理岩體開挖的模型，並與王泰典(2003)之FLAC數值預測結果相比較，驗證本文除了可對節理岩體的力學特性進行仿真外，亦可對於隧道圍岩的異向性與彈塑性變形進行合理預測。最後則是針對三維尺度下隧道開挖時的前進面效應以及不同節理走向時的隧道開挖案例進行模擬，並加以探討其合理性。
數值分析研究結果顯示：節理之位態及組數影響岩體強度與變形性甚鉅，隨節理走向與傾角不同，岩體之強度和變形性均呈現高度異向性，其中破壞模式預測結果亦顯示節理位態與組數常係決定岩體的破壞行為的要素。此外，於隧道開挖過程中，節理空間分布亦對隧道之變形性以及圍岩降伏區域有著關鍵性的影響，隧道開挖後對圍岩產生徑向解壓、切向加壓的應力調整特性，除了可能導致完整岩材破壞外，亦常使平行隧道環向的節理面因正向應力減小導致滑動破壞的機率增大，且由於完整岩材與節理面剪力行為於峰後長具有軟化的特性，因此圍岩降伏區域的擴大往往引致隧道產生大量的變形。

關鍵字

等值連續體 ； 隧道變形 ； 節理岩體 ； 組成模式 ； 峰前峰後變形 ； 破壞模式 ； 節理異向性

並列摘要

It is usual to face collapse and squeezing engineering disaster during tunnel excavation. Except considering the excavating disturbance to the tunnel, tunnel deformation control and yielding area distribution of surrounding rock mass are also the important indexes on engineering design. Based on the concept of modern tunneling method, the excavation-induced stress of the rock masses surrounding a tunnel would achieve its strength because of the influence from complicated factors including in-situ stress, intact rock nature, excavation method and so on. It will cause the deformation surrounding the tunnel significantly increases and extremely influence the tunnel clearance after the rock masses surrounding the tunnel achieve peak strength, inducing squeezing failure in some cases.
This research considers many factors which influence the elastic-plastic deformation behavior like joints distribution and mechanical characteristic of intact rock and joints. After that, it constructs a 3D numerical constitutive model based on the concept of equivalent continuum according to physical jointed rock mass model from previous study. In addition, this research simulates the laboratory uniaxial test about jointed rock mass and uses 2D numerical simulation results from previous study for verification.
For the verification about uniaxial compressive test for jointed rock masses, this research uses FLAC3D to simulate the physical experiment done by Yang in 1992 with the related conditions as well as modified parameters. And verifies the simulation results with the theoretical model proposed by Wang in 2003.
For the parts about tunnel excavation, this research simulates the tunnel excavation in two joint sets rock masses with extremely high joint normal stiffness first and then verifies the results with analytical solutions proposed by Kirsch in 1989. After that, this research simulates cases regarding tunnel excavation in rock masses with different sets of joints and compare the simulation results with FLAC’s results done by Wang in 2003. For the purposes of proving that numerical model established in the research has not only the ability to describe the mechanical behaviors of jointed rock masses but also the ability to predict the anisotropy and elastic-plastic deformation surrounding a tunnel. Finally, this research will simulate the cases regarding tunnel excavation in jointed rock masses with different strikes as well as the behaviors about advancing effect. And discuss the rationality of the prediction results.
Research outcomes reveal that the strength and deformability of rock masses are highly influenced by the attitudes and the number of joint sets. Both strength and deformability of rock masses have significant anisotropy with various strike and dip angles of joint sets. Among the characteristic of jointed rock masses, the prediction about failure modes also reveals that the attitudes and the number of joint sets are the essentials to determine the failure behavior. Furthermore, the spatial distribution of joint sets significantly influences the deformation of tunnel and the yield region of rock masses surrounding the tunnel too. Tunnel excavation causes the stress adjustment, i.e., radial decompression and tangential compression, resulting in not only the failure of intact rock but also the sliding of joint sets parallel to the circumferential direction of tunnel because of the decreasing normal stress. Moreover, for the reason that both intact rock and joints usually exhibit the characteristic of strain-softening in post-peak behavior, the enlargement of yield region regarding the rock masses surrounding tunnel frequently induces significant deformation on tunnel.

並列關鍵字

Equivalent continuum ； Deformation surrounding a tunnel ； Jointed rock mass ； Constitutive model ； Pre- and post-peak deformation ； Failure mode ； Joint-induced anisotropy

參考文獻

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