| With the rapid development of transportation in Southwest my country,a series of tunnel projects with complex working conditions and difficult construction have also appeared continuously.How to ensure safe production in the process of tunnel excavation has become an urgent problem to be solved.At the same time,microseismic monitoring technology is becoming more and more mature.It uses sensors to receive seismic waves generated by the rupture of tunnel surrounding rock,analyzes and obtains related information on the time,space,intensity,and focal mechanism of microseismic events,and monitors and early warnings of underground engineering disasters.It has become recognized in the industry.One of the effective methods for monitoring the stability of surrounding rock during tunnel excavation.Compared with traditional monitoring technology,microseismic monitoring technology can realize remote,full-area,real-time and dynamic monitoring,and has the advantages of analyzing the trend of rock mass destruction,the location of unstable bodies,and early warning.This paper uses the Wenquan Tunnel in the extension section of the Zunyi-Suiyang Expressway in Guizhou Province and the No.1 Tunnel in Qichong Village,1.5Ring Qianchun Avenue,Guiyang City as the supporting project,and introduces the microseismic monitoring technology into the construction safety monitoring of the shallow soft rock tunnel.Real-time monitoring and analysis of rock stability and surface vibration response of blasting construction.The main work and research results include:(1)A microseismic monitoring system suitable for drilling and blasting construction of shallow buried highway tunnels has been constructed.Shallow-buried highway tunnel are summarized,microseismic monitoring system in the process of building all the major points for rock burst release of micro wave propagation path through the tunnel hollowed section,sometimes leading to locate phrase,put forward the method of joint surface and tunnel arrangement sensor,and performance monitoring system is verified by blasting test point location,found that the larger degree of the positioning precision is improved,At the same time,the mutual interference between tunnel construction and microseismic monitoring is reduced.(2)Through field microseismic data processing,the source parameter characteristics of microseismic events in shallow buried soft rock tunnel are analyzed.It is found that,compared with the known hard rock tunnel,the moment magnitude,corner frequency,stress drop are smaller,and the source radius is larger.Meanwhile,there is a strong correlation among the source parameters.It is also found that the frequency of microseismic events with large moment magnitude increases and the main frequency of microseismic events shifts to low frequency in the process of tunnel surrounding rock instability.(3)Through the analysis and study of the focal mechanism solution of microseismic events in the process of typical tunnel surrounding rock instability,the process of rupture germination,development and transfixion of tunnel surrounding rock is interpreted.According to the P-wave initial motion inversion results of microseismic events,the focal mechanism solution of rock mass fracture is calculated,and the development trend of rock mass fracture and the direction of principal stress in the fracture area are obtained.Combined with the geological information of the tunnel,the macro failure mode of the surrounding rock can be accurately analyzed.The analysis of the collapse accident in Wenquan tunnel shows that the failure of surrounding rock along the structural plane of rock mass and the orientation of rock formation is caused by the regional dynamic load in the process of instability of surrounding rock mass,and the wedge-shaped collapse is formed along the free surface of the tunnel,which is basically consistent with the situation of the site collapse.(4)The negative effects of blasting vibration on the health of surface structures and structures during tunnel drilling and blasting are evaluated.The surface sensor array in the microseismic monitoring system is used flexively to monitor and record the seismic waves arriving at the surface of the tunnel during blasting construction.The safety assessment of surface structures is carried out through the peak vibration velocity(PGV)and corner frequency(f_c)of the surface seismic waves,and the multifunctional application of the microseismic monitoring technology is realized.At the same time,through the regression analysis method and dimensional analysis method,the empirical formula of surface PGV and f_c prediction under the working condition of this project is obtained,which guides the on-site blasting construction. |
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