Research On Rockburst Evolutionary Process And Energy Dissipation Characteristics

Rockburst has posed a serious threat to the coal mine safety and high efficiencyproduction. Along with the increase of mining depth and mining intensity, rockburst hasbecome increasingly severe and complex. Rockburst is a sudden and violent release of energystored in rock mass and geological structures, results from quick break of coal and rock undertheir own physical and mechanical changes and external stress, and is a typical irreversibleenergy dissipation and release process. Thus, this paper attempts to discuss the revolution ofrockburst from the point of energy dissipation. The time domain features of energy dissipationduring the coal and rock failure process are experimentally studied; on this basis, thetime-space evolutionary process of rockburst activity domain system(RADS) is analyzed, anda dynamic pressure type of rockburst evolutionary model is built; with the model, theevolution of stress, displacement and energy fields of the system are studied after pressurerelief, and site verifications are carried out.The energy types and transformation law in coal and rock failure process are analyzed,the energy dissipative characteristics of coal and rock are studied under uniaxial compressionprocess, and the influencing factors are investigated. Results indicate that deformation andfailure of coal and rock correspond to its internal energy change, and external force work bymeans of its self-organization of energy accumulation, release and dissipation. The cumulativevalue of EMR energy and that of corresponding dissipated energy well subject to the form ofy=alnx+b, and EMR as a measurable parameter can analyze and invert the internal energydissipation of coal and rock. The failure process of coal and rock loaded shows significantphased energy dissipation characteristics. The factors that influence the energy dissipationinclude material strength, homogeneous degree and energy input efficiency.The concept RADS is proposed, and the two dimensional spatiotemporal entropy as wellas energy dissipation of the system are analyzed. The energy and entropy balance equations ofrepresentative volume element(RVE) of coal mass in main rockburst activity domain system(MRADS) are derived based on dissipative structure theory, and the stability are analyzed.Conclusions show that entropy flow and production reflect temporal-spatial evolution of theinternal structures in the system; their algebraic relations show a good judgment in rockburstwhether or not happens. The massive existence of elastic energy caused by the poor path ofenergy dissipation is the potential energy source resulting in rockburst. The intrinsic energychange of REV of coal mass mainly depends on heat flow and internal force variation inMRADS; the internal always spontaneous realize a irreversible process with low utilization ratio energy alternate that of the higher, with the development of which, MRADS will enterthe nonlinear region far from balance state and turn into rockburst potential region. Thestability of the system can be judged by a certain state of the excess entropy production duringthe process of thermodynamics.A dynamic pressure type of rockburst evolutionary model is built based on energydissipation. The periodic cracks initiation strength parallel to the maximum principal stressdirection and damage strain energy in limited area are calculated in MRADS; the formation ofthe spallation structure and stability are discussed, and the minimum critical load andaccumulating elastic energy before are obtained; the failure of the spallation structure underdifferent degrees of perturbation and the generation of rockburst are analyzed. On this basis,two kinds of typical dynamic perturbation(main roof pressure and blasting) are numericallysimulated for validating the model, and the EMR data are used for site verification to theevolution of RADS.The evolution laws of stress, displacement and energy fields of pressure relieved MRADSare studied theoretically and site verified using EMR method. Results indicate that, pressurerelief by water jet can greatly reduce the scopes of stress concentration and energyaccumulation, which can avoid forming energy-storage structure, and result in dissipatingenergy of coal seam; it also makes the high press far away from coalface, which ensures thestability of the whole coal mass.The results have important theoretical and practical significance for deep understandingthe mechanism and further exploring forecasting and control methods of rockburst.