水-力耦合和隔离状态下孔道砂岩力学特性的对比

Comparsion on mechanical properties of hollow sandstones under hydro-mechanical coupling and isolation conditions

岩石的水力学特性与矿山突水灾害密切相关,为揭示不同的水岩力学相互作用,对比研究在水-力耦合与隔离2种不同力学状态下孔道砂岩力学特性的差异性。采用MTS815岩石力学试验系统,进行不同围压和孔压下孔道砂岩的常规三轴压缩试验。整个试验围压σ3分成10,20,30 MPa共3个系列,每个系列围压试验中,孔压P设为4个级别,分别是围压σ3的20%,40%,60%和80%。对水-力耦合下的岩石试件用热缩管进行包裹,对水-力隔离下的岩石试件加装隔水装置,在三轴静水压力状态(σ1=σ2=σ3)下采用0.005 mm/s的加载率对试件进行轴向加载,直到试件破坏。结果表明:水-力耦合状态下,孔道砂岩的峰值偏应力强度、扩容起始偏应力、残余偏应力强度和变形模量与围压呈正相关关系,与孔压呈负相关关系,而泊松比的关系则正好相反,试件呈现出明显的单一剪切面破裂,破裂角分布在53°~69°变化;水-力隔离状态下孔道砂岩峰值偏应力强度、扩容起始偏应力和残余偏应力强度均与围压和孔压在总体上呈正相关趋势,水-力隔离状态下试件破裂角变化不明显;在一定的围压与孔压下,处于水-力耦合下试件峰值偏应力强度和变形模量在总体上低于水-力隔离状态下的相应量值,而泊松比的关系则正好相反,随孔压的增加,2种力学状态下的岩石力学特性差异越大。水-力隔离状态内孔壁施加适量应力可以明显提高试件的三轴承载力。

The hydraulic characteristics of rock are closely related to mine water inrush disaster.To reveal different water-rock interactions,a comparative study of the mechanical properties of rocks under two different conditions:hydro-mechanical coupling and hydro-mechanical isolation in the process of full stress-strain is conducted.The MTS815 rock mechanics test system is used to perform the conventional triaxial compression tests under different confining pressures and pore pressures.The confining pressureσ3 is divided into three series of 10,20 and 30 MPa.In each series of confining pressure tests,the pore pressure P is set to four levels,which are 20%,40%,60%,and 80%of the confining pressureσ3,respectively.The rock specimen under hydro-mechanical coupling is wrapped with a heat shrinkable tube,a water-proof device is added to the rock specimen under hydro-mechanical isolation.Under triaxial hydrostatic pressure state(σ1=σ2=σ3),the test specimen is axially loaded with a loading rate of 0.005 mm/s,until the test piece is broken.The results show that under hydro-mechanical coupling condition,peak deviatoric stress,initial expansion deviatoric stress,residual deviatoric stress and deformation modulus of specimens are positively related to confinement,however,negatively related to with pore pressure,while the Poisson’s ratio has the opposite relationship,specimens fail along single fracture plane with an angle ranging from 53°to 69°.Under hydro-mechanical isolation condition,the peak deviatoric stress,initial expansion deviatoric stress,and residual deviatoric stress of specimens have positive correlations with the confinement and pore pressure,the fracture angle of specimens does not change obviously.At the same confinement and pore pressure,the peak deviatoric stress,initial expansion deviatoric stress,and deformation modulus of specimens under hydro-mechanical coupling are lower than those under hydro-mechanical isolation condition,while the Poisson’s ratio has an opposite relationship.The differences of rock mechanical properties under two conditions are larger with the increase of pore pressure.The triaxial bearing capacity of the specimen can be significantly improved by applying appropriate stress on the inner wall of hollow sandstone under hydro-mechanical isolation condition.