| With the country's inclusion of the Sichuan-Tibet Railway construction project in the national 13 th Five-Year Plan key construction projects,a number of tunnel construction projects with complex engineering geological conditions and difficult construction will emerge.Due to the complex geological structure and frequent waterbearing geological hazards,the tunnel construction has brought huge challenges,making our country one of the countries that suffer the most from water-bearing geological disasters.Probing in advance the geological structure in front of the tunnel and the geological formation with poor water content have become key problems that need to be solved in tunnel and underground engineering construction.Aiming at the above-mentioned engineering construction difficulties,the numerical analysis and field tests were performed to analyze the source of artificial hammering.The threedimensional observation system suitable for shallow-buried and buried tunnel digging in rich water is studied through three aspects: excitation parameters,arrangement parameters and receiving parameters.Based on the theory of seismic wave propagation,the stress-strain relationship of elastic solid media,and Darcy's theory based on dualphase media,the problem of advanced water exploration by seismic wave method is studied.The geological forecasting system constructed in the Pearl River Delta Intercity Railway Tunnel will be used for field geological forecasting experiments and applications,and the following research results will be obtained.The hammer source has the characteristics of low frequency,good continuity in the shallow layer,strong penetrability,directivity,and few interference waves,etc.It can be used as an artificial source for soft rock tunnels in water-rich areas.The field test results show that the use of a seismic source pad can significantly improve the energy and uniformity of the seismic signal.An 18-pound hammer and a 20cm×20cm steel pad are the best shock-absorbing tools for artificial sources.A three-dimensional observation system suitable for the "NATM" excavation is proposed.The geophone and the source location are spread out on the double-sided excavation tunnels that are excavated quickly according to the area.The distance between the focal points is 1.5m to 2m.According to the basic theory of seismic wave propagation and the stress-strain relationship in elastic solid media,the relationship between the instantaneous amplitude and frequency of the seismic wave and the solid stress gradient is obtained.Based on the simplified dual-phase medium model and the Darcy theory of hydrodynamics,a quantitative identification method of geological poor water content based on directional prediction of dual-phase medium is proposed.Based on the actual geological forecast test results of the two inter-city tunnels in the Pearl River Delta and the actual revealed results of the palm surface,the system and system are accurate in predicting the geological conditions ahead,especially for poor water-bearing geology,which is sensitive and does not produce surrounding rocks Disturbance and high work efficiency have good promotion value. |
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