True-triaxial test on unloading failure of jointed rock bridge

Jointed rock slopes under excavation unloading may studdenly lose the stability due to the high stress accumulated in the rock bridge of the slope. In order to simulate the influence of jointed rock bridge and different intermediate principal stresses on the strength and failure mode of rock slopes under excavation unloading, the uniaxial compression and true-triaxial unloading tests on granite specimens with different rock bridge length were carried out on the true-triaxial test system. The stress-strain curves, peak strength, crack propagation, failure mode, acoustic emission(AE) characteristics and peak intensity of AE were analyzed with the aid of high speed camera and AE system. The results show that, compared with uniaxial loading in the uniaxial loading the brittle failure is more obvious in the true-triaxial loading and unloading. With the increase of the length of the rock bridge, the peak strength of the sample, the energy released at the time of failure and the AE rate are all increased. Under different intermediate principal stresses, the compressive strength of the specimen increases with the increase of the intermediate principal stress but the peak value of the AE is reduced, which is resulted from that the lateral pressure caused by the intermediate principal stress makes the internal structure of the rock more compact and the micro-cracks difficult to develop. The influence mechanisms of rock bridge length and intermediate principal stress were revealed by the superposition method of intensity factor in fracture mechanics. The true-triaxial test can simulate the stress state of rock excavation unloading more realistically. © 2018, Science Press. All right reserved.