A Model for Anisotropic Shear Strength of Rock Joints

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Title:	A Model for Anisotropic Shear Strength of Rock Joints
Authors:	葛瑞伯;Thapa, Gaurab Singh
Contributors:	土木工程學系
Keywords:	異向性剪力強度;粗糙節理;岩石節理;裂隙;直剪試驗;PFC;Anisotropic shear strength;Joint roughness;Rock joint;Fracture;Direct shear test;PFC
Date:	2020-08-19
Issue Date:	2020-09-02 14:35:31 (UTC+8)
Publisher:	國立中央大學
Abstract:	本文以法向荷重為定值(CNL)的條件下，研究岩石節理異向性剪力行為。由於Barton剪力強度公式以及 Tse和Cruden的公式皆無法考慮岩石節理異向性剪力強度，因此提出新的公式解決此問題。 τ=σ_n tan⁡〖[ϕ_b+13.41Z_2log10⁡(JCS/σ_n ) ]+C_b* C_AR 〗由於粗糙節理在不同方向具有異向性，因此本研究使用 Z_2(一階倒數的均方根)求粗糙節理係數 (JRC) 與最大剪力強度 (τ)，粗糙度參數包含剪力方向 (β°)，波長 (λ)，振幅 (A) 和循環數量 (N)， Z_2愈大代表粗糙度愈主導。 Z_2=√(1/2πN ∫_(x=0)^(x=2πN)▒(dy/dx)^2 )=√((A^2 sin⁡(β) (8Nπ^2 sin⁡(β)+λ sin⁡((8Nπ^2 sin⁡(β))/λ) ))/(Nλ^2 ))/2 　　本研究使用三種驗證模式對提出的模型進行適當的論證：(1)透過顆粒流軟體PFC^3D (Particle Flow Code^3D)生成不同振幅 (2mm，3mm，4mm) 與波長 (9mm，12.86mm，18mm和30mm)的正弦曲線的粗糙節理，在不同的剪力方向進行驗證； (2)用PFC^3D模擬不同傾角的三角形節理來驗證此模型； (3)使用Zhang（2019）的實驗數據對提出的模型進行了驗證。結果顯示不同的驗證結果皆與此模型高度吻合，由於剪力方向的粗糙度發生變化，岩石節理的剪力強度 (τ) 本質上異向性的。 ;In this study, an anisotropic shear behavior of rock joints is investigated under constant normal load condition (CNL). Barton’s shear strength formula together with Tse and Cruden’s equation cannot take into account the anisotropic shear strength of rock joints. This study proposed a new equation taking in account anisotropic shear behavior of rocks joints. τ=σ_n tan⁡〖[ϕ_b+13.41Z_2log10⁡(JCS/σ_n ) ]+C_b* C_AR 〗 Because of anisotropic characteristics of joint roughness in different direction, roughness parameter Z2 (root mean square of the first derivative) is derived based on sinusoidal profile parameters and is used to find Joint roughness coefficient (JRC) and peak shear strength (τ). The parameters of roughness under consideration are shearing direction (β⁰), Wavelength (λ), Amplitude (A) and Number of cycle (N). A bigger value for this parameter (Z2) means a roughness is more dominant. Z_2=√(1/2πN ∫_(x=0)^(x=2πN)▒(dy/dx)^2 )=√((A^2 sin⁡(β) (8Nπ^2 sin⁡(β)+λ sin⁡((8Nπ^2 sin⁡(β))/λ) ))/(Nλ^2 ))/2 Different modes of validation were used for suitable justification of the proposed models. PFC3D numerical simulation on sinusoidal profile with different amplitudes (2mm, 3mm and 4mm), wavelengths (9mm, 12.86mm, 18mm and 30mm) and normal stresses at different shearing direction (β⁰) is performed for the validation. In addition, the proposed model is validated with PFC3D numerical simulation results of triangular joints profile with different inclination angle. Furthermore, proposed model is also validated with the experimental data of Zhang, 2019. Except few combinations, good agreement is found between the results from proposed model and results from different modes of validation. It is found that shear strength of rock joint is anisotropic in nature due to roughness variation in shearing direction.
Appears in Collections:	[Graduate Institute of Civil Engineering] Electronic Thesis & Dissertation

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