花岗岩三轴循环加卸载宏细观特性的三维颗粒流模拟
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摘要
为研究三轴循环加卸载条件下花岗岩破坏全过程的宏细观力学特性,采用颗粒流PFC3D方法确定了应力-应变曲线上的应力门槛值(σ_(ci)起裂应力、σ_(cd)裂隙损伤应力和σ_f峰值强度),分析了宏观参数随塑性剪切应变的变化规律,并结合微裂纹数目及微裂纹发展变化过程,揭示了微裂纹损伤演化规律。结果表明:宏观上,不同围压下相应的σ_(ci)/σ_f分别为49.59%、49.7%、36.3%,σ_(cd)/σ_f分别为91.74%、95%、96.2%;应力门槛值和弹性模量随塑性剪切应变的增加先快速减小后趋于稳定,泊松比随塑性剪切应变的增加先快速增大后趋于稳定。细观上,微裂纹数目最大增量发生在应变软化阶段;试样内部微裂纹的发展是通过其自身扩展实现的,且微裂纹的扩展同时受试样结构和试样内主应力方向的影响;不同围压下试样均在残余变形阶段发生剪切破坏。研究结果很好地揭示了试样在循环荷载作用下破裂的全过程。
In order to study the macro-micro mechanical properties of granite failure under triaxial cyclic loading and unloading,the critical thresholds(the crack initiation stressσci,the crack damage stressσcdand the peak stressσf)on stress-strain curves were determined,the variation law of macroscopic parameters with the plastic shear strain was analyzed,and the damage evolution law of micro-cracks was revealed by combining the number of micro-cracks and the process of micro-cracks propagation based on PFC3D method.The results showed that,from macro perspective,the corresponding σ_(ci)/σ_f under different confining pressures was 49.59%,49.7%,36.3%,respectively,and σ_(cd)/σ_f was 91.74%,95% and 96.2%,respectively.With the increase of plastic shear strain,the critical thresholds stress and elastic modulus decreased rapidly and then tended to be stable,while the Poisson's ratio increased rapidly and then tended to be stable.From micro perspective,the maximum increment of the number of micro-cracks occurred during the strain softening stage.The development of the microcracks was realized by its own expansion,which was affected by both the specimen structure and the principal stress direction in the specimen.Moreover,the shear failure occurred in the residual deformation stage under different confining pressures.The research results well revealed the whole process of specimen damage under cyclic loading.
In order to study the macro-micro mechanical properties of granite failure under triaxial cyclic loading and unloading,the critical thresholds(the crack initiation stressσci,the crack damage stressσcdand the peak stressσf)on stress-strain curves were determined,the variation law of macroscopic parameters with the plastic shear strain was analyzed,and the damage evolution law of micro-cracks was revealed by combining the number of micro-cracks and the process of micro-cracks propagation based on PFC3D method.The results showed that,from macro perspective,the corresponding σ_(ci)/σ_f under different confining pressures was 49.59%,49.7%,36.3%,respectively,and σ_(cd)/σ_f was 91.74%,95% and 96.2%,respectively.With the increase of plastic shear strain,the critical thresholds stress and elastic modulus decreased rapidly and then tended to be stable,while the Poisson's ratio increased rapidly and then tended to be stable.From micro perspective,the maximum increment of the number of micro-cracks occurred during the strain softening stage.The development of the microcracks was realized by its own expansion,which was affected by both the specimen structure and the principal stress direction in the specimen.Moreover,the shear failure occurred in the residual deformation stage under different confining pressures.The research results well revealed the whole process of specimen damage under cyclic loading.
引文
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[11]赵星光,李鹏飞,马利科,等.循环加、卸载条件下北山深部花岗岩损伤与扩容特性[J].岩石力学与工程学报,2014,33(9):1740-1748.
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[13]苏承东,熊祖强,翟新献,等.三轴循环加卸载作用下煤样变形及强度特征分析[J].采矿与安工程学报2014,31(3):456-461.
[14]张帆.三峡花岗岩力学特性与本构关系研究[硕士学位论文][D].武汉:中国科学院武汉岩土力学研究所,2007.
[15]Brace W F,JR Paulding B W,Scholz C.Dilatancy in the fracture of cryslline rocks[J].Journal of Geophysical Research,1966,71(16):3939-3953.
[16]Hoek E,Bieniawski Z T.Brittle fracture propagation in rock under compression[J].International Journal of Fracture,1965,1(3):137-155.
[17]Hallbalter D K,Wagner H,Cook N G W.Some observations concerning the microscopic and mechanical behaviour of quartzite specimens in stiff,triaxial compression tests[J].International Journal of Rock Mechanics and Mining Sciences and Geomechanics Abstracts,1973,10(6):713-726.
[2]Eberhardt E,Stead D,Stimpson B.Quantifying progressive pre-peak brittle fracture damage in rock during uniaxial compression[J].International Journal of Rock Mechanics and Mining Sciences,1999,36(3):361-380.
[3]Martin C D.Strength of massive Lac du Bonnet granite around underground openings[D].Winnipeg:University of Manitoba,1993.
[4]Martin C D,Chandler N A.The progressive fracture of Lac du Bonnet granite[J].J.Rock Mech.Min.Sci.Geomech.Abstr.,1994,31(6):643-659.
[5]周家文,杨兴国,符文熹,等.脆性岩石单轴循环加卸载试验及断裂损伤力学特性研究[J].岩石力学与工程学报,2010,29(6):1172-1183.
[6]徐速超,冯夏庭,陈炳瑞.矽卡岩单轴循环加卸载试验及声发射特性研究[J].岩土力学,2009,30(10):2929-2934.
[7]杨永杰,宋扬,楚俊.循环荷载作用下煤岩强度及变形特征试验研究[J].岩石力学与工程学报,2007,26(1):201-205.
[8]刘建锋,谢和平,徐进,等.循环荷载作用下岩石阻尼特性的试验研究[J].岩石力学与工程学报,2008,27(4):712-717.
[9]苏承东,杨圣奇.循环加卸载下试样变形与强度特征试验[J].河海大学学报(自然科学版),2006,34(6):667-671.
[10]谢红强,何江达,徐进.岩石加卸载变形特性及力学参数实验研究[J].岩土工程学报,2003,25(3):336-338.
[11]赵星光,李鹏飞,马利科,等.循环加、卸载条件下北山深部花岗岩损伤与扩容特性[J].岩石力学与工程学报,2014,33(9):1740-1748.
[12]彭瑞东,鞠杨,高峰,等.三轴循环加卸载下煤岩损伤的能量机制分析[J].煤炭学报,2014,39(2):245-252.
[13]苏承东,熊祖强,翟新献,等.三轴循环加卸载作用下煤样变形及强度特征分析[J].采矿与安工程学报2014,31(3):456-461.
[14]张帆.三峡花岗岩力学特性与本构关系研究[硕士学位论文][D].武汉:中国科学院武汉岩土力学研究所,2007.
[15]Brace W F,JR Paulding B W,Scholz C.Dilatancy in the fracture of cryslline rocks[J].Journal of Geophysical Research,1966,71(16):3939-3953.
[16]Hoek E,Bieniawski Z T.Brittle fracture propagation in rock under compression[J].International Journal of Fracture,1965,1(3):137-155.
[17]Hallbalter D K,Wagner H,Cook N G W.Some observations concerning the microscopic and mechanical behaviour of quartzite specimens in stiff,triaxial compression tests[J].International Journal of Rock Mechanics and Mining Sciences and Geomechanics Abstracts,1973,10(6):713-726.