Study On Rockburst Mechanism In Rock Mass With Structural Planes And Comprehensive Prediction Method

Rockburst is one of the geological hazards of dynamic instability under high geostress conditions during underground engineering excavation.In the process of underground chamber excavation,the stress of surrounding rock is relieved and brittle failure occurs due to the formation of the open face.The elastic strain energy stored in rock mass suddenly release,which results in the phenomena of burst loosening,spalling,ejection and even throwing.Rockburst seriously threatens the safety of constructors and equipment,affects the construction progress,causes over-excavation,primary support failure,and even induces earthquakes in serious cases.Rockburst may occur instantaneously or continue after the excavation of the underground chamber is completed.Rockburst seriously threatens the life safety of construction workers because of its suddenness,uncertainty and unpredictability.Rockburst problem widely exists in the process of underground chamber construction,which seriously restricts the development of economic construction.Therefore,it is of great significance to scientifically and effectively study the occurrence mechanism and occurrence conditions of rockburst in the process of underground engineering construction,study the possibility of rockburst in rock mass,and accurately predict rockburst for actual production.In this paper,the rockburst mechanism and law of rock mass with structural planes in underground chamber excavation are studied by means of indoor test,numerical simulation and theoretical research,and a rockburst prediction method based on comprehensive weight and extension method is proposed.The specific research works are as follows:(1)Based on the similarity theory,quartz sand,barite powder,gypsum powder,cement and water are selected as the raw materials and similar materials suitable for the rockburst model test are configured by orthogonal proportioning tests and physical mechanics tests.Combined with the physical mechanics parameters of the original rock in the project area and the laboratory excavation conditions,the similarity ratio of model test and the final ratio of similar materials are determined.Then,four working conditions of none structural plane,single structural plane,multiple structural planes and through structural plane are designed,the structural plane is simulated,and the corresponding rockburst model tests are carried out.By means of monitoring the stress and displacement information of the monitoring points in the excavation process and combined with the phenomena observed in the test process,the failure mode and failure law of the surrounding rock are studied,and the rockburst occurrence mechanism of rock mass with structural planes in underground chamber excavation is analyzed.(2)According to the prototype size of actual engineering,the numerical model of chamber excavation is established by using the numerical simulation software FLAC3D,and the rock masses with none structural plane,single structural plane,multiple structural planes and through structural plane are simulated by using the setting of contact surface.The numerical calculation of chamber excavation is carried out by using the same excavation method as the model test.The stress and displacement curves and distribution cloud charts of surrounding rock monitoring point during the simulation tunnel excavation are obtained.The change laws of stress and displacement of surrounding rock in the excavation process are analyzed,and the numerical simulation results are compared with the model test results,which verifies the accuracy of model test.At the same time,the failure mode and failure law of surrounding rock in the chamber excavation process of rock mass with different structural planes are obtained.(3)According to the conditions required for rockburst occurrence,five main influencing factors including uniaxial compressive strength,stress coefficient,brittleness coefficient,elastic energy index and integrity of rock mass are used as the evaluation indexes of rockburst prediction.The assessment index system of rockburst intensity is constituted.Then,the analytic hierarchy process(AHP)and variation coefficient methods are used to determine the comprehensive weight of evaluation index,and the rockburst prediction model is established based on the extension evaluation method.Thirdly,the parameter programming and numerical calculation of the proposed prediction model are carried out in the MATLAB software.The user visualization execution window and software system of rockburst prediction model are realized.Finally,the software system is applied to the rockburst prediction in the water diversion tunnels of Jiangbian hydropower station and Jinping secondary hydropower station.The prediction results are compared with the actual situation and other evaluation methods to verify the accuracy and applicability of the model.