Experimental Investigation On The Characteristics Of Burst Ejection Under Uniaxial Compressive Stress

Since the evaluation of the deep underground excavations the rockburst became one of the major hazards.This hazard may lead to fatal and costly incidents to the mining industry.Maohua Xialiyuan coal industry limited company gave the opportunity to study the rockburst prone rock types present in the vicinity of the mine.In China,the depth of underground mining and tunneling has exceeded at greater extent which produces the higher frequency of rockburst occurrence.There are many rockburst incidents reported in different underground excavation projects and the consequences are fatal and costly.Therefore,the researchers and professionals are striving hard to overcome this deadly hazard.Three different rock types were selected to investigate the rockburst characteristics under the uniaxial compressive stress.The rockburst properties of each rock type were determined based on the monitoring system which includes,High Speed Camera,Acoustic Emission Count Rate,Stress – Strain Curves,Infrared Thermograph and Static Resistance Strain Gauge.The results show that each rock type behaved differently under the loading condition as well as the bursting properties of each rock differs from other type of rocks,because of the different composition,granular characteristics and nature of rock type.Additionally,the velocity of the ejected piece(s)from the surface of the core samples was determined in order to estimate the potential threat may cause by the ejected piece(s)with higher velocities.Initially,there were three core samples prepared in laboratory for each rock type.In other words,there were nine samples in total for experimental investigation.The coal sample 1 under the UCS data was lost because of the machine error,so the analysis is done on two coal samples only.However,the sandstone and limestone each have three core samples for experiment based analysis.Based on fracture mechanics,the failure of the rock samples and ejection of piece(s)was distributed in three stages,like crack initiation,propagation and coalescence of the cracks.The crack initiation is initial stage of developing potential failure plane;the propagation is intermediate stage of developing wing cracks,an independent or a combination of shear and tensile crack(s);the final stage is coalescence in which all cracks connect with each other and forming a separate piece to be separated from the parent core sample.Among all the core samples,the coal samples found to have more shearing failure mode and both samples failed at very low stress loading value as compare to the other type of rocks samples.Further,the limestone and sandstone samples failed in slabing or spalling,buckling and toppling manner because of high stress values.The ejection of piece(s)from core sample was/were monitored closely to determine the velocity of ejection.The coal samples and sandstone samples demonstrated considerable ejection of few small and large piece(s)with certain velocities.However,the limestone samples failed to produce ejected piece(s)except only one core sample which was ejected with minimum velocity and covered least distance.This research study is an initial examination of the rockburst prone rock type present in the vicinity of the Maohua Xialiyuan coal industry limited company.However,the findings are limited because of the small number of samples,but it confirms the possibilities of the rockburst prone characteristics of the rock types selected for the experiments.