Experimental Study On Influence Of Initial Damage On The Disturbance Triggered Rockburst Under Loading Conditions

Rockburst is a typical geological disaster accompanied by rocks ejection during underground excavation.It mainly caused by ground stress release.Based on the triggering mechanism,the rockbursts can be classified into self-initiated rockburst and disturbance triggered rockburst[1].According to the amplitude of external dynamic disturbance,the disturbance triggered rockburst can be divided into those that are intensive and those that are slight.The slight disturbance triggered rockburst(hereafter referred to as rockburst)is rock ejection failure phenomenon.It occurr in the surronding rocks that are in a critical state of rockburst after stress redistribution and was triggered by remotely slight dynamic disturbance.Moreover,the disturbance triggered rockburst is also closely related to the damage and integrity of the rock masses.Relevant studies have indicated that rockburst occur in the damaged rock masses.Meanwhile,artificial increasing damage of rock masses during underground excavation at depth can control the occurrence and intensity of rockburst.Therefore,it is important to investigate the influence of damage on rockburst.Rectangular prismatic granite specimens with different damages were prepared using a method of cooling the specimens treated with high-temperature.A self-developed servo dynamic true-triaxial testing apparatus was used to conduct the one free face true-triaxial dynamic rockburst test.The pregnant process of remotely triggered rockburst with different damages was simulated,and the influence of damage on ejection process,kinetic energy,failure form and rock fragments was investigated.The obtained results can be taken as a reference to reveal the influence of damage on triggered rockburst.Some significant conclusions are displayed as follows.1.When the initial damage exceeds a certain value,strainburst,instead of remotely triggered rockburst,will occur caused by static stress before applying dynamic disturbance.2.For a constant initial damage,only when static stress is equal to or higher than a special threshold,remotely triggered rockburst occurs.For constant static stress and dynamic disturbance,and static stress less that the special threshold,with increasing initial damage of rock specimen,the remotely triggered rockburst can be much more easily induced by dynamic disturbance.3.The kinetic energy of triggered rockburst increases first and then decreases with the increasing of initial damage of rock specimen.The kinetic energies under the condition of rock specimen with D of 0.2,0.3 and 0.4 are higher than that under the condition of rock specimen with D of 0.6 and 0.7.When the D is 0.3,the kinetic energy is the highest.Moreover,as the D increases in the value range less than 0.3,the average size of rock fragments shows a minor increase.For the D beyond 0.3,the average size of rock fragments decreases rapidly with the increasing D.4.A proper rock damage will increase the proneness of remotely triggered rockburst and promotes a more intensive rockburst.