不同围压下断续预制裂纹粗晶大理岩变形和强度特性的试验研究

EXPERIMENTAL STUDY ON DEFORMATION AND STRENGTH PROPERTIES OF COARSE MARBLE WITH DISCONTINUOUS PRE-EXISTING CRACKS UNDER DIFFERENT CONFINING PRESSURES

通过在MTS815.03岩石力学伺服试验机上对断续预制裂纹粗晶大理岩进行常规三轴压缩试验,基于试验结果研究不同围压下断续预制裂纹粗晶大理岩的变形和强度特性。结果表明,随着围压的增加,完整岩样和断续预制裂纹岩样峰后表现从应变软化逐渐转化为理想塑性的变形特性;岩石峰值环向应变对围压的敏感程度高于峰值轴向应变;强度与围压之间的关系可采用Coulomb准则来表征,且残余强度对围压的敏感性显著高于峰值强度。粗晶大理岩晶粒尺度较大,完整岩样的杨氏模量随围压而增大,峰值应变与围压之间成正线性关系;而断续预制裂纹岩样的杨氏模量以及峰值应变和围压之间的关系较为复杂,且随裂纹倾角而变化。单轴压缩时,断续预制裂纹岩样峰值强度与裂纹倾角密切相关,其最大轴向承载能力取决于两条预制裂纹内部顶端的扩展模式以及晶粒间的摩擦滑移;较低围压(σ3≤10MPa)时,与完整岩样的峰值强度相比,断续预制裂纹岩样的峰值强度明显偏低,但残余强度相差不大;而较高围压(σ3>10MPa)时,岩样进入塑性流动阶段后,完整岩样和预制裂纹岩样的三轴强度(峰值强度和残余强度)相差很小,粗晶大理岩样的轴向承载极限与预制裂纹分布关系不大,晶粒间的摩擦承载决定粗晶大理岩的强度特性。

Experiments were carried out to study coarse marble with discontinuous pre-existing cracks under conventional triaxial compression by the MTS815.03 rock mechanics servo-controlled testing machine. Based on the experimental results, the deformation and strength properties of coarse marble with discontinuous pre-existing cracks under different confining pressures were investigated. The results show that the deformation of intact rock specimens and marble with discontinuous pre-existing cracks after peak strength changes from strain softening into ideal plasticity. The sensitivity of peak circumferential strain to the confining pressure is higher than that of peak axial strain. The relation between strength and confining pressure can be expressed by Coulomb criterion; what＇s more, the sensitivity of residual strength to the confining pressure is higher than that of peak strength. The coarse marble has greater crystal in size of 4 - 6 mm. The Young＇s modulus of intact rock specimen increases with theconfining pressure; and the peak strain has a positive linear relation with the confining pressure. However, the Young＇s modulus and the peak strain of rock specimen with discontinuous pre-existing cracks have more complex relations with the confining pressure and vary with the crack angles. In uniaxial compression, the peak strength of rock specimen with discontinuous pre-existing cracks has a close relation with the crack angles; and the maximal axial stress depends on the fracture modes between the inner tip of two pre-existing cracks and friction slips between crystals. Under lower confining pressure（σ3〈 10 MPa）, the triaxial peak strength of rock specimens with discontinuous pre-existing cracks is lower than that of intact rock specimens; but for triaxial residual strength, there are no great differences between intact coarse marble and marble with discontinuous pre-existing cracks. However, under higher confining pressure（σ 3〉 10 MPa）, the triaxial strengths（peak strength and residual strength） of intact rock specimen are approximately same as those of rock specimen with discontinuous pre-existing cracks, which shows that the supporting capacity of coarse marble specimen is only related to the confining pressure but no relation with the distribution of pre-existing cracks. The internal friction force determines the strength property of coarse marble.