页岩抗张力学行为各向异性实验与理论研究

Experimental and theoretical investigation on anisotropy of shale tensile mechanical behaviors

开展彭水龙马溪页岩声波波速、巴西劈裂和声发射监测实验,明确页岩模量、抗张强度、声发射、破坏模式各向异性特征,并基于各向异性抗张强度CPA理论,分析页岩抗张强度及破裂角影响因素及变化规律。研究结果表明:1)随着加载角θ(加载方向与页岩层理面的夹角)增加,纵横波波速逐渐降低,抗张强度逐渐增加,破坏模式出现"简单-复杂-简单"的转变;2)随着微观参数Ω0(表征页岩强度空间分布)的增加,抗张强度逐渐增大,破裂角βf(破坏面与基准线的夹角)在θ较小时逐渐增大,在θ较大时逐渐减小;3)径向应力对抗张强度及破裂角也有显著影响,随着径向压应力增加,抗张强度增加、βf逐渐减小,而随着径向拉应力增加,抗张强度降低、βf逐渐增大;4)随着抗张强度各向异性程度增加,抗张强度与βf逐渐增大,并且βf最大值会由较小θ逐渐偏向较大的θ。

Acoustic velocity,Brazilian split testing and acoustic emission monitoring experiments were conducted for LMX shale at Pengshui region in Chongqing.The anisotropic characteristics of elastic modulus,tensile strength,acoustic emission and failure model were specified,and the influencing factors and changing rules of shale tensile strength and failure angle were analyzed based on CPA theory for anisotropic tensile strength.The results show as follows.1)With the increase of θ(the angle between loading direction and shale’s bedding plane),longitudinal and shear wave velocity decrease gradually but the tensile strength gradually increases,and shale’s failure model shows a shift trend of"simple-complexity-simple".2)With the growing of microscopic parameter Ω0(representing shale strength spatial distribution),both tensile strength and failure planeβf(the angle between the failure surface and baseline)at lower loading angle θ increase,but the latter decrease at higher θ.3)Radial stress also has a significant effect on tensile strength and failure angle.As radial compressive stress increases,tensile strength increases and βf decreases,but with the increase of radial tensile stress,tensile strength decreases and βf gradually increase.4)As tensile strength anisotropy increases,tensile strength andβ_f gradually increase,and the maximum value of βf gradually shifts from the smallerθto the largerθ.