软硬互层岩体结构面宏细观剪切力学特性

Investigation on the macro-meso shear mechanical properties of soft-hard interbedded rock discontinuity

针对“软+硬”和“硬+软+硬”组合形式下的2类典型软硬互层岩体结构面,通过开展恒定法向压力下的室内直剪试验和PFC^(2D)细观模拟,研究了不同含水率、法向压力及一阶起伏角下结构面的宏细观剪切力学特性,据此提出了其剪切强度估算公式并进行了算例验证分析。研究表明:①结构面剪切应力(法向位移)随剪切位移的变化具有显著阶段性发展特征,即第1类结构面历经初始非线性压剪变形、应力稳定增长压剪变形和应力陡升-脆落塑性压剪变形3个阶段,第2类结构面历经初始非线性压剪变形、应力陡-缓升压剪变形和应力恒定塑性压剪变形3个阶段;②2类结构面的峰值(残余)剪切强度和峰值剪切位移均随含水率增加而减小(最大法向位移则增大);2类结构面的峰值(残余)剪切强度和峰值剪切(最大法向)位移均随法向压力增加而增大;第1类结构面的峰值剪切强度随一阶起伏角增加而增大(残余剪切强度则先增大后减小),第2类结构面的峰值(残余)剪切强度随一阶起伏角增加而增大,且2类结构面的峰值剪切位移总体上均随一阶起伏角增加而减小(最大法向位移则增大);③2类结构面的细观损伤裂纹数量(能量)随剪切位移的变化均可划分为3个发展阶段,即初期微增、中期近似“下凹弧形”陡增和后期近似线性缓增(裂纹数量)以及初期微增、中期近似“上凹弧形”缓增和后期近似线性陡增(能量);④宏观试验结果与PFC^(2D)细观模拟结果吻合较好,统一概化描述了结构面宏细观损伤劣化机理,并将第1类和第2类结构面的典型破坏模式分别概括为压剪-起裂破坏、错动-脱空破坏和贯通-啃断破坏以及压剪-起裂破坏、磨损-啃断破坏和贯通-滑移破坏各3种基本类型;第1类和第2类结构面的细观损伤颗粒分别近似呈“倒U形”和“S形”分布于剪切面附近,且颗粒间接触力倾角于0°~90°时损伤颗粒数量分布最多;⑤着重考虑硬性岩层起伏度的影响,提出了2类结构面的剪切强度估算公式,并采用极限平衡法和强度折减法对含典型结构面的边坡算例进行了稳定性分析,验证了该公式的合理性。

For the two kinds of typical soft-hard interbedded rock discontinuities such as“soft+hard”(the first kind)and“hard+soft+hard”(the second kind),the macro-meso shear mechanical properties of those under different moisture contents,normal stress and first-order asperity angle were investigated using laboratory direct shear tests and PFC^(2D) meso-mechanics simulation(under constant normal load),based on which the shear strength estimation formula was proposed and verified.Research shows that①the change of shear stress(normal displacement)with shear displacement has remarkable characteristics of stage develop-ment.Three stages are found in the two kinds of rock discontinuities respectively.For the first kind of discontinuity,the three stages include initial nonlinear compression-shear deformation,increases steadily of stress and increases steeply-drops brittlely of stress.For the second kind of discontinuity,the three stages consist of initial nonlinear compression-shear deformation,increases steeply-slowly of stress and constant stress.②The peak(residual)shear strength and peak shear displacement decrease as the moisture content increases(the maximum normal displacement increases).The peak(residual)shear strength and peak shear(maximum normal)displacement increase as the normal stress increases.When the first-order asperity angle increases,the peak shear strength of the first kind discontinuity increases(the residual shear strength increases first and then decreases),while the peak(residual)shear strength of the second kind discontinuity increases,and the peak shear displacement of both kinds of discontinuity decreases generally(the maximum normal displacement increases).③The change of meso-damage crack number and energy with shear displacement can be divided into three stages,i.e.,a slight,an approximately“down concave arc-shape”steep and a linear slow increase in the initial,middle and later stage respectively(crack number),and a slight,an approximately“up concave arc-shape”slow and a linear steep increase in the initial,middle and later stage respectively(energy).④The test data are in good agreement with the simulation results,and the macro-meso damage degradation mechanism of rock discontinuity is generally described.The typical failure modes of the two kinds of discontinuity can be summarized as three basic types respectively,i.e.,compression-shearing-cracking failure,dislocating-voiding failure and penetrating-gnawing failure as well as compression-shearing-cracking failure,and wearing-gnawing failure and penetrating-slipping failure.The meso-damage particles of the two kinds of discontinuity are distributed in an approximately“inverted U-shaped”and“S-shaped”near the shear plane respectively,and when the angle of contact force between particles is between 0°and 90°,the number of damaged particles is the most.⑤According to the limit equilibrium and strength reduction methods,the rationality of shear strength estimation formula for the rock discontinuity(considering the impact of first-order asperity angle)is verified by the stability analysis of rock slope examples.