Study On Failure Mechanism And Prediction Method Of Rockburst

With the rapid development of transportation,water conservancy and mining industry in China,more and more rock mass excavations are carried out in high stress environment.In the process of engineering excavation in high ground stress area,geological disasters such as rockburst are often encountered.Rockburst is a sudden and highly destructive disaster,which is a serious threat to the safety of equipment and construction personnel.Therefore,rockburst related topics have been research focus of geotechnical engineering at home and abroad.The ultimate purpose of rockburst research is to guide construction and control the risk of rockburst.Through the research on failure mechanism and prediction methods of rockburst,critical instability criteria of different rockburst failure modes can be obtained and possible rockburst intensity grades can be predicted,thus providing a basis for rockburst prevention and control.Therefore,based on catastrophe theory and principle of minimum potential energy,the critical instability criteria of two typical rockburst failure modes,tensile cracking and sliding and slab buckling,are derived in this paper.Meanwhile,through the systematic analysis of engineering geological conditions,formation conditions and development process of rockburst,main factors affecting rockburst are determined,and the corresponding evaluation indicators are selected and classification standards are modified,thus the evaluation system of rockburst prediction is constructed;Combining information entropy method with gray relation projection method,the weight of evaluation indices are determined by information entropy method,and the gray relation projection values are calculated and graded by gray relation projection method.The prediction model of rockburst intensity based on entropy weight and gray relation projection method is constructed.The accuracy and applicability of the model are verified by several engineering examples at home and abroad.The main research results and innovations of this paper are as follows:(1)The simplified mechanical model of tensile cracking and sliding rockburst is analyzed by using fold catastrophe model,and the result are compared with the analytical result of cusp catastrophe model in previous studies and the solution of stability theory for mechanical system.The results show that the analytical result of fold catastrophe model is consistent with stability theory for mechanical system,but different from cusp catastrophe model,and it is concluded that cusp catastrophe model is not suitable for analyzing tensile cracking and sliding rockburst by analyzing causes for the differences.Finally,an engineering example is used to verify rationality,and the results are consistent with the actual situation,which verifies the correctness of using fold catastrophe model to analyze tensile cracking and sliding rockburst.(2)In order to overcome the shortcomings of the existing mechanical models of slab buckling rockburst,such as ignoring the interaction between the split rock plates,a thin plate mechanical model of circular tunnel considering the horizontal stress between rock plates is established.The bending deflection of rock plate under load is calculated by using principle of minimum potential energy,and compared with the ultimate deflection of tensile failure,thus the depth of rockburst failure is obtained.The rationality of the model is verified by an engineering example,and the results are closer to the actual situation than the existing model,which shows that the study has certain reference value.(3)Through the systematic analysis of engineering geological conditions,formation conditions and development process of rockburst,it is proposed that the main factors affecting the occurrence of rockburst include stress level,properties of surrounding rock and development of groundwater;Based on the above factors,according to information contained in each evaluation index,four evaluation indices including ??/?c,?c/?t,Wet and Kv are selected,and the classification standard of Wet is modified,thus a evaluation system for rockburst prediction is bulit.(4)Combining information entropy method with gray relation projection method,the weight of evaluation indices are determined by information entropy method,and the gray relation projection values reflecting the degree of correlation are calculated and graded by gray relative projection method,and then the entropy weight-gray relation projection model for prediction of rockburst intensity is established.The model is tested by measured data of several projects at home and abroad,and the results are in good consistent with the actual situation,which shows that the model is of high accuracy and applicability,and has certain prospect of engineering application.