摘要
对采自重庆鱼嘴的砂岩开展若干围压(最小10 MPa、最大130 MPa)的保持轴压不变峰前卸围压试验,并与同围压下的常规三轴压缩试验结果进行对比分析,研究砂岩卸荷过程中的变形特征、破坏形态、峰值强度与残余强度特性及其扩容参数演化特征。主要研究成果为:(1)加载路径下,围压增至130 MPa时,应力-应变曲线不出现应力降,可以认为围压130 MPa为砂岩脆-延转化压力。(2)加载破坏时,偏应力峰值前扩容量相对于峰后较小,但卸荷破坏偏应力峰值前则表现出较大的扩容量。(3)相同初始应力条件下,卸荷破坏时偏应力变化量比加载破坏时大,证明卸荷应力路径更容易引起砂岩试样的破坏。(4)相同围压下,卸荷破坏的破裂角大于加载破坏。(5)卸荷条件下得出的抗剪强度参数c比加载条件下低1.2%,?值则高4.8%;不论卸荷还是加载,残余变形阶段c值都大大减小,?值则变化不大。(6)围压对扩容的约束作用较显著,围压越大,剪胀角极值越小;卸荷开始后,剪胀角呈剧烈增加态势,迅速达到极值;剪胀角峰值与偏应力峰值不同步,前者滞后于后者;卸荷破坏剪胀角峰值比加载破坏剪胀角峰值大,且达到峰值经历的塑性剪切应变量相对较小,证明卸荷破坏的剪胀性更加显著。这些结论可揭示高应力条件下砂岩的卸荷力学特性,为西部深埋引水隧洞的开挖、支护设计及其稳定性分析提供理论参考。
A series of pre-peak unloading tests on sandstone from Chongqing Yuzui under the range of initial confining pressure between 10 MPa and 130 MPa have been carried out,in order to analyze rock deformation behavior,failure deformation,peak strength and residual strength criterion,the evolvement property of dilatancy parameter during the process of unloading.The conventional triaxial compression tests of sandstone have been also performed.The results show that：（1） The triaxial compression tests performed under different confining pressures discover that the stress drop of the stress-strain curves does not appear when confining pressure reaches above the value of 130 MPa;so it can be considered as the transition point of brittleness and ductility.（2） Under conventional compression,the dilatancy amount at the pre-peak of deviatoric stress is smaller compared with post-peak;while under unloading stress path,the sample exhibits greater dilatancy amount at pre-peak of deviatoric stress.（3） Under the same initial stress,the variation in stress required for rock unloading failure is comparably less than that oftriaxial compressive process, which reveals that unloading stress path make sandstone sample more prone to failure. （4） Under the same confining pressure, the rupture angle of unloading failure is greater than that of loading failure. （5） Shear strength parameters have been evaluated by Coulomb laws; it is found that the cohesion c decreases, but the inner friction angle increases during unloading; under the two loading stress paths, the cohesion c decreases greatly and the inner friction angle has a little change at the residual deformation stage. （6） The restriction on the behavior of dilatancy by confining pressure is significant, when the confining pressure is higher, the peak dilatancy angle would be smaller, the dilatancy angle increases quickly to the peak after the beginning of unloading~ the peaks of deviatoric stress and the dilatancy angle exhibit a time asynchrony; moreover, the f
出处
《岩石力学与工程学报》
EI
CAS
CSCD
北大核心
2011年第3期473-479,共7页
Chinese Journal of Rock Mechanics and Engineering
基金
国家自然科学基金资助项目(40672192
50479072)
水利部公益性行业科研专项项目(201001009)
关键词
岩石力学
卸荷
三轴压缩
砂岩
高围压
扩容
rock mechanics
unloading
triaxial compression
sandstone
high confining pressure
dilatancy
