| Most of the rock masses in underground engineering are in a complex threedimensional stress state,and they also contain a large number of joints,cracks and faults.In the three-dimensional stress state,these structures often become the source of rock mass micro-fracture and even macro-fracture.On the one hand,it greatly reduces the strength of the rock mass,and on the other hand,it is very likely to induce rock bursts,rock bursts,and large deformations of surrounding rock compression.And major engineering disasters such as instability and roof collapse.Therefore,studying the damage and destruction process of fractured rocks under true triaxial conditions has very important scientific significance and practical value for revealing the mechanism of rock mass catastrophe in underground engineering,and also helps to understand the failure characteristics of rock mass deformation and fracture catastrophe more deeply.mechanism.This paper conducts true triaxial tests on a complete sandstone sample and a sandstone sample with five prefabricated penetrating cracks(inclination angles of 30° and90°),and uses acoustic emission technology to monitor the damage and failure process of the rock sample in real time and analyze it systematically.The mechanical and acoustic emission parameter characteristics,crack damage evolution process and fracture behavior of the complete sandstone sample and the sandstone sample with five prefabricated through cracks(inclination angles of 30° and 90°)under the true triaxial test conditions are discussed.The research results of this paper are as follows:(1)Analysis of mechanical properties of complete and fractured sandstone samples.Under the same confining pressure,the peak strength and elastic modulus of the90° fractured sandstone sample are higher than the 30° fractured sandstone sample.Compared with intact sandstone samples,the presence of prefabricated throughfractures has a significant weakening effect on the strength of sandstone,and the30°sandstone samples have the highest degree of deterioration.(2)Analysis of acoustic emission characteristics of complete and fractured sandstone samples.1)Based on the characteristic stress thresholds obtained from the analysis of the mechanical and acoustic emission characteristics of the intact and fractured sandstone specimens,the damage and failure process of the intact and fractured sandstone specimens under true triaxial conditions can be divided into the fracture closure stage,the crack initiation stage,and the stability Crack growth stage,unstable crack growth stage and post-peak softening stage.2)The acoustic emission event rate of the intact and fractured sandstone samples in the stable crack propagation stage has an obvious "U"-shaped evolution path,while in the unstable crack propagation stage,an inverted "U"-shaped evolution path appears;The evolution characteristics of the emission event rate may be mechanically related to the microstructure characteristics such as the grain size of the sandstone.3)The number of cumulative acoustic emission events at the peak stress of the intact sandstone sample is greater than that of the fractured sandstone sample.The average amplitude of the intact and fractured sandstone sample at the stress drop has a sharp increase,and the acoustic emission b value is greatly reduced at this time,Which shows that the number of large-scale cracks in the rock sample at the stress drop increases significantly.4)Intact and fractured sandstone specimens,only tensile cracks were generated in the fracture closure stage,while tensile cracks and shear cracks were generated in the unstable crack propagation stage and post-peak softening stage.(3)Analysis of failure characteristics of intact and fractured sandstone specimens and analysis of crack propagation connection mode of fractured sandstone specimens.1)The crack growth pattern of the intact sandstone sample on the medium principal stress loading surface is distributed in layers,and is roughly axisymmetrically distributed on both sides of the middle of the sample.The crack growth patterns of fractured sandstone specimens on the medium principal stress loading surface are mainly divided into two types: one is a far-field crack that is not connected to the prefabricated crack,and the other is formed by the crack propagation from the tip of the prefabricated crack.Crack.2)Both the 30° fractured sandstone sample and the 90° fractured sandstone sample formed a fracture surface dominated by shear cracks under the same confining pressure.For the rock bridge area,both of them showed compression connection(C mode),and All are formed by the penetration of inclined cracks. |
PDF Full Text Request