| 摘要: | 裂隙岩體中存在不連續面，如節理、斷層、層理等，因為不連續面的優選方位，使得力學性質具有高度的方向性，稱為異向性（anisotropy）。構築於裂隙岩體中的工程，其工程行為不僅與裂隙方位有關，同時工程配置方向也會顯著地影響工程行為，如岩石隧道的開挖方向、條形岩石基礎長軸的配置方位、岩坡的斜交角等，稱之為異向性工程行為。裂隙岩體工程行為之異向性早已被列入工程實務的考量之中，例如：RSR、RMR及SMR等均有方位評分之調整。上述方位評分調整具有簡易且良好執行性，廣泛被工程師應用於工程實務上。然而，評分調整的基準可能基於創立者的工程經驗，雖廣為使用，但欠缺學理及實驗驗證。
岩石異向性深具學術研究之旨趣，長期以來吸引眾多學者投入試驗及理論研究。解析解途徑僅能針對理想、簡易的問題求得解析解，難以適用於真實複雜的工程問題。異向性岩石無論是小試體或物理模型試驗，涉及方位因子（如：裂隙傾角????、工程配置角γ），所需試體數量遠超過等向性岩石，在執行上有相當大的困難度。三維數值模擬或可解決解析解及物理模型的難處，但在執行數值模擬時，仍須針對施工程序進行適當的模擬（逐階模擬），方可全面合理地呈現岩石工程異向性行為。
本文採用合成岩體（Synthetic Rock Mass, SRM）架構，利用三維離散元素軟體PFC3D（Particle Flow Code in three Dimension）建立完整岩體模型，並配合離散裂隙網絡（Discrete Fracture Network, DFN），分別建構隧道及基礎合成岩體模型，以更細緻之裂隙傾角（????）及工程配置角（γ），全面探討其對岩石工程異向性行為的影響。本文主要的研究範疇包括：
（1） 利用合成岩體模型探討單階模擬（one-step simulation）與逐階模擬（step-by-step simulation）之合理性及適用性。
（2） 利用合成岩體模型針對更細緻之隧道斜交開挖方向（γ）進行模擬，以全面瞭解開挖方向對隧道穩定性之影響。
（3） 利用數值模擬結果以最佳化之方式，與既有岩石隧道方位評分調整基準進行擬合，驗證或佐證其合理性及正確性。
（4） 利用數值模擬結果建立岩石隧道及岩石基礎方位評分調整之連續方程（Continuous Function, CF）。
本文主要研究成果臚列如下：
（1） 異向性岩石工程行為之模擬，必須採用三維模型並配合施工程序進行逐階模擬，方能合理地完整呈現方位因子（????及γ）對岩石工程之影響。
（2） 數值模擬的數據顯示，低傾角裂隙岩體在某些斜交開挖方向下，其穩定性相當不佳，僅考慮正交開挖及平行開挖的情境，可能遺漏了最不穩定的組合，故斜交開挖情境下之模擬及分析有其必要性。
（3） 本文根據數值模擬的結果，提出岩石隧道及岩石基礎方位評分調整之連續方程。
;Fractured rock masses contain discontinuities such as joints, faults, and bedding planes, which may cause their mechanical or engineering behaviors with anisotropies due to the preferred orientations of discontinuities. Nowadays, rating adjustments for orientation in rock engineering practice, such as RSR, RMR, and SMR, provide evaluations of construction quality under various fracture dips (????) and engineering configuration orientations (γ). However, these existing rating adjustments were established based on engineering experiences, which don′t have enough relevant scientific and experimental validations. Additionally, the classifications of ???? and γ in these rating adjustments adopted discrete functions that only provide rough ratings of it. Furthermore, the study of the impact of γ in tunnel excavation is not sufficient, e.g., only three directions of excavation in fractured rock masses were investigated.
This paper provides improved rating adjustments for orientation in tunnel excavation and foundation bearing capacity by analyzing two series of 3D numerical simulations that consist of various ???? and γ. The synthetic rock mass (SRM) framework, using the bonded particle model (BPM) as an intact rock mass coupled with the smooth joint model (SJM) as fracture mechanical behaviors with geometry given by discrete fracture network (DFN), is adopted to construct the 3D synthetic tunnel and foundation rock mass model, respectively, herein. Then, a series of radial displacements of a tunnel under various ???? and γ simulating by step-by-step excavation, and a series of bearing capacity of foundation under various ???? and γ simulating by the bearing capacity test, can be obtained. We optimize the numerical simulation results and existing rock tunnel rating adjustment for orientation to obtain the modified rating adjustment based on the RMR system. Finally, this paper provides the continuous functions of modified rating adjustments for tunnel excavation and bearing capacity, respectively, using multiple regression analysis. According to the simulation and analysis results, the conclusion of this paper can be drawn:
（1） The 3D numerical modeling is necessary for simulating the engineering behaviors of fractured rock due to 3D models can comprehensively present the impacts of ???? and γ on it.
（2） For tunnel excavation simulation, using step-by-step excavation is more reasonable than using one-step excavation, which means that simulating practical engineering problems needed to consider the construction process.
（3） Low-dip fractured rock masses exhibit significant instability under some oblique excavation directions, their radial displacements may exceed the orthogonal and parallel excavation scenarios. Therefore, the rating adjustments for orientation are necessary to consider oblique excavation scenarios.
（4） The proposed continuous functions of modified rating adjustments for tunnel excavation and bearing capacity provide computational convenience and improve the previous rating adjustments′ precision and accuracy.
Illustrative examples of how to employ the proposed rating adjustments are given at the end. |
