初始内聚力及摩擦角对岩样全部变形特征的影响
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摘要
目的研究初始内聚力及摩擦角对剪切带图案及岩样全部变形特征的影响.方法采用FLAC内嵌语言FISH编制了计算平面应变压缩岩样轴向、侧向、体积应变及泊松比的FISH函数.在峰值强度之前及之后,岩石的本构模型分别取为线弹性模型及莫尔库仑剪破坏与拉破坏复合的应变软化模型.结果随着初始内聚力及摩擦角的增加,破坏模式由复杂向简单剪切破坏转变;发生破坏的单元数目降低;剪切带倾角增加;轴向应力的峰值强度及所对应的轴向、侧向应变的绝对值降低,岩样可以达到的最小体积增加.峰后的轴向应力-轴向应变曲线、轴向应力-侧向应变曲线、侧向应变-轴向应变曲线、泊松比-轴向应变曲线及体积应变-轴向应变曲线的斜率几乎不受初始内聚力及摩擦角的影响.但是,当初始内聚力及摩擦角最小时,5种峰后曲线略显平缓,这是由于发生破坏的单元数目最多及剪切带的倾角最低.结论剪切带倾角更接近Arthur倾角,说明了数值结果是可信的.岩样失稳破坏的前兆不随着初始内聚力及摩擦角的降低或增加而改变.
Influences of initial cohesions and friction angles on shear band(SB)patterns and entire deformational characteristics were investigated.FISH functions were written and embedded in FLAC to calculate axial,lateral and volumetric strains as well as Poisson′s ratio of rock specimen in plane strain compression.In linear strain-softening stage beyond the linear elastic stage,a composite Mohr-Coulomb criterion with tension cut-off was used.Numerical results show that the increase of initial cohesion and friction angle leads to 1)transition of failure modes from complex to simple shear failures;2)decrease in the number of yielded elements;3)increase in SB′s inclination;4)decrease in the peak strength of axial stress and the corresponding axial strain as well as the absolute value of lateral strain;5)increase in the minimum volume that rock specimen can obtain.The post-peak slopes of the axial stress-axial strain curve,the axial stress-lateral strain curve,the lateral strain-axial strain curve,the Poisson′s ratio-axial strain curve,and the volumetric strain-axial strain curve nearly do not depend on the initial cohesion and friction angle.However,when initial cohesion and friction angle are the lowest,the five kinds of post-peak curves become slightly ductile owing to the lowest SB′s inclination and the largest area of the yielded zone.The SB′s inclination is closer to the Arthur′s inclination,reflecting the reasonability of the present predictions.No apparent difference in precursor to the instability failure of rock specimen is observed for different initial cohesions and friction angles.
Influences of initial cohesions and friction angles on shear band(SB)patterns and entire deformational characteristics were investigated.FISH functions were written and embedded in FLAC to calculate axial,lateral and volumetric strains as well as Poisson′s ratio of rock specimen in plane strain compression.In linear strain-softening stage beyond the linear elastic stage,a composite Mohr-Coulomb criterion with tension cut-off was used.Numerical results show that the increase of initial cohesion and friction angle leads to 1)transition of failure modes from complex to simple shear failures;2)decrease in the number of yielded elements;3)increase in SB′s inclination;4)decrease in the peak strength of axial stress and the corresponding axial strain as well as the absolute value of lateral strain;5)increase in the minimum volume that rock specimen can obtain.The post-peak slopes of the axial stress-axial strain curve,the axial stress-lateral strain curve,the lateral strain-axial strain curve,the Poisson′s ratio-axial strain curve,and the volumetric strain-axial strain curve nearly do not depend on the initial cohesion and friction angle.However,when initial cohesion and friction angle are the lowest,the five kinds of post-peak curves become slightly ductile owing to the lowest SB′s inclination and the largest area of the yielded zone.The SB′s inclination is closer to the Arthur′s inclination,reflecting the reasonability of the present predictions.No apparent difference in precursor to the instability failure of rock specimen is observed for different initial cohesions and friction angles.
引文
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[10]王学滨,潘一山,盛谦,等.动力应变局部化传播及尺寸效应数值模拟[J].计算力学学报,2002,19(4):500-503.
[11]王学滨.平面应变压缩岩样侧向变形特征数值模拟[J].岩土工程学报,2005,27(5):525-530.
[12]王学滨,赵扬锋,代树红,等.地震块体模型的共轭剪切破裂带数值模拟[J].防灾减灾工程学报,2004,24(2):119-125.
[13]王学滨.地震前兆特征与岩样剪切应变率异常数值模拟[J].大地测量与地球动力学,2005,25(1):102-107.
[14]Finno R J,Harris W W,Mooney M A,et al.Strainlocalization and undrained steady state of sand[J].Journal of Geotechnical Engineering,ASCE,1996,122(6):462-473.
[15]朱建明,徐秉业,岑章志.岩石类材料峰后滑移剪胀变形特征研究[J].力学与实践,2001,23(5):19-22.
[2]Ord A,Vardoulakis I,Kajewski R.Shear band forma-tion in Gosford sandstone[J].Int.J.Rock Mech.Min.Sci.&Geomech.Abstr.,1991,28(5):397-409.
[3]Vardoulakis I.Shear band inclination and shear mod-ulus of sand in biaxial tests[J].Int.J.Num.Anal.Method Geomech.,1980,4(2):103-119.
[4]王学滨,潘一山,杨小彬.准脆性材料试件应变软化尺度效应理论研究[J].岩石力学与工程学报,2003,22(3):188-191.
[5]Wang Xuebin,Pan Yi-shan.Effect of relative stresson post-peak uniaxial compression fracture energy ofconcrete[J].Journal of Wuhan University of Tech-nology-Materials Science Edition,2003,18(4):89-92.
[6]王学滨,马剑,刘杰,等.基于梯度塑性本构理论的岩样侧向变形分析(I):基本理论及本构参数对侧向变形的影响[J].岩土力学,2004,25(6):904-908.
[7]王学滨,刘杰,王雷,等.基于梯度塑性本构理论的岩样侧向变形分析(Ⅱ):尺寸效应及弹性会跳[J].岩土力学,2004,25(7):1127-1130.
[8]田军,李桂臣,王杰.用点荷载实试验确定岩基抗压强度标准值[J].沈阳建筑工程学院学报,2000,16(2):101-104.
[9]王学滨.基于梯度塑性理论的岩样峰后变形特征研究[J].岩石力学与工程学报,2004,23(增1):4292-4295.
[10]王学滨,潘一山,盛谦,等.动力应变局部化传播及尺寸效应数值模拟[J].计算力学学报,2002,19(4):500-503.
[11]王学滨.平面应变压缩岩样侧向变形特征数值模拟[J].岩土工程学报,2005,27(5):525-530.
[12]王学滨,赵扬锋,代树红,等.地震块体模型的共轭剪切破裂带数值模拟[J].防灾减灾工程学报,2004,24(2):119-125.
[13]王学滨.地震前兆特征与岩样剪切应变率异常数值模拟[J].大地测量与地球动力学,2005,25(1):102-107.
[14]Finno R J,Harris W W,Mooney M A,et al.Strainlocalization and undrained steady state of sand[J].Journal of Geotechnical Engineering,ASCE,1996,122(6):462-473.
[15]朱建明,徐秉业,岑章志.岩石类材料峰后滑移剪胀变形特征研究[J].力学与实践,2001,23(5):19-22.
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