岩石破损过程强度变化规律实测研究

EXPERIMENTAL STUDY OF STRENGTH EVOLUTION LAWS IN ROCK FAILURE PROCESS

岩石材料强度会随着破裂发展而逐渐衰减,详细介绍自行设计的岩石强度衰减测试方法,试验思路、试件制作及关键技术;通过自行设计的直剪试验,测得常规压缩试验破裂得到的不规则损伤岩块在直剪过程中的剪应力-压应力关系曲线,由其拟合得到库仑强度曲线,并与已有(单、三轴)压缩试验数据线性拟合得到的莫尔强度包络线进行比较,分析讨论岩石在破损过程中材料强度(黏聚力和内摩擦角)变化规律,澄清现有黏聚力和内摩擦角变化规律2种完全相对立观点的适用范围。研究结果表明,由完整岩样进行单、三轴试验测得的黏聚力明显大于不规则岩块直剪试验结果,这主要是岩样在单、三轴压缩破坏过程中产生的损伤所致,而不是试验方法所导致的偏差;黏聚力反映的是岩石本质强度特性,受不同应力状态的影响较小。岩样单、三轴压缩试验测得的内摩擦角小于岩块直剪试验结果,这主要是受到不同应力状态和岩石缺陷分布的影响。在岩石破损过程中,内摩擦角随损伤的发展具有先快速增大至最大值后大幅降低直至保持一定趋势不变的规律。内摩擦角反映的是岩石摩擦强度特性,受不同应力状态的影响较大。黏聚力对应力水平的敏感程度远小于内摩擦角。岩石在破裂前后自身材料强度会产生明显衰减。

Rock material strength will degrade with the damage in rock failure process. This paper reports one self-designed method to test rock strength degradation and introduces the technical routine, sample preparation and its key technique in detail. Through self-designed direct shear tests, the relationships between shear stress and compressive stress of irregular damaged rock samples which are produced in common uniaxial and triaxial compressive experiments are obtained; and a Coulomb strength curve can be gained by the linear regression through compression-shear testing data. A comparison between the Coulomb strength curve and the ultimate Mohr circle envelope linearly-regressed by previous uniaxial and triaxial compressive experimental data is performed; and the evolution laws of material strength（cohesion and internal friction angle） in rock failure process are analyzed and discussed. The application scopes of two kinds of completely reverse evolution laws of cohesion and intemal friction angle are clarified through the analysis and discussion. The research results show that the cohesion measured by uniaxial and triaxial experiments of intact rock samples is obviously greater than that obtained by direct shear tests of irregular rock blocks. This difference mainly resulted from the damage in rock failure processes of uniaxial and triaxial compressive experiments, not from the deviation between different testing methods. Cohesion reflects rock intrinsic strength characteristic, slightly influenced by different stress states. The internal friction angle obtained by uniaxial and triaxial experiments is smaller than that gained by direct shear tests of rock blocks. This difference mainly resulted from the influence of different stress states and rock flaw distribution. Internal friction angle increases rapidly to the maximum and decreases steeply to keep a certain stable trend in rock failure process. Internal friction angle reflects rock frictional strength characteristic, heavily influenced by different stress states. The sensitivity of cohesion to stress level is far lower than that of internal friction angle. The material strength itself degrades obviously before and after rock failure.