拉剪作用下类岩石试样的力学特性与损伤破坏机制

Mechanical properties and failure mechanisms of the rocklike specimens under tension shear effects

利用自主设计的拉伸-剪切辅助装置,开展不同法向应力(-0.28~3.0MPa)条件下的拉剪试验和压剪试验,同时利用声发射技术对比分析两者的力学特性与损伤破坏机制。研究结果表明,拉伸-剪切辅助装置能够较好地开展拉剪试验。试样的峰值应力随法向应力呈曲线变化,对法向拉应力更为敏感,Hoek-Brown强度准则总体上能够较好地表征全应力区的强度特征。拉剪试样峰后应力大幅跌落并迅速分离成两部分,与压剪试验峰后残余阶段相比,具有更多的脆性破坏特征。试样破裂面的形貌特征与法向应力的方向以及大小密切相关,压剪试样破裂面的破碎程度以及声发射参数表征的损伤程度均大于拉剪试验。相比于拉剪试样,压剪试样的破裂面摩擦区、局部剥落现象更明显。随法向应力增大,声发射平静期持续时间变长,试样进入裂纹非稳定扩展阶段的时间越晚。拉剪试验损伤过程各阶段所需时间相较于压剪试验更短,损伤破坏的速率更快。剪应力曲线临界点σcc、σci和σcd与声发射参数可分别表征试样的宏观与微观破裂过程,σcd临界点和声发射b值可作为岩石破坏的预兆。

Using self-designed tension shear auxiliary device,we carried out a tension shear test and a compression shear test under different normal stresses between-0.28 MPa and 3.0 MPa.We applied acoustic emission to compare and analyze the mechanical properties and the damage failure mechanisms of the specimens for both tests.The main results are listed as below.The tension shear auxiliary device can help us carry out the tension-shear test well.The peak stress varies with the normal stress non-linearly and is more sensitive to the normal tensile stress.The Hoek-Brown strength criterion can generally characterize the strength of the full stress area.The post-peak stress of the specimen in tension shear test drops severely and separates into two parts rapidly,showing the failure characteristics with more brittleness than that of the compression shear test.The morphological characteristics of the fracture plane are closely related to the direction and magnitude of normal stress.For compression shear test,the damage degree represented by the acoustic emission parameters is greater,as well as the failure degree of the fracture plane,compared with those observed in tension shear test.The frictional area and the local spalling of the fracture plane are also more obvious for the specimens in compression shear test,compared with those in tension shear test.As the normal stress increases,the duration of the acoustic emission quiet period gets longer,and the start time of the unstable crack propagation gets later.Compared with the compression one,the tension shear test shows a shorter duration time for each stage of the failure process as well as a higher failure rate.The critical points σcc,σci and σcd of the shear-stress plot and the acoustic emission parameters can represent,respectively,the macroscopic and microscopic failure process of the specimen.The critical point σcd and the acoustic emission b value can be used as omens of rock failure.