STUDY OF ADVANCE GEOLOGICAL PREDICTION EFFECTS WITH DIFFERENT GEOPHYSICAL METHODS—TAKING A LARGE EMBEDDED DEPTH DOUBLE SHIELD TBM TUNNEL IN SOUTHEAST TIBET FOR EXAMPLE

Some geophysical prediction methods has different suitability when using in the double shield TBM(tunnel boring machine) affected by the double shield TBM equipment, construction technology. We analyze the suitability of different geophysical methods in double shield TBM advance geological prediction. Taking a double shield TBM tunnel with large embedded depth in southeast Tibet for example, we studied the application effect of EH4(high frequency magnetotelluric method),ISP(integrated seismic prediction),HSP(horizontal sound probing) and improved TRT(tunnel reflection tomography) in advance forecast of the tunnel. Used as a macro forecasting tool, EH4 can find large-scale unfavorable geological body. ISP and HSP are used as active and passive sources methods, could provides a more accurate prediction for the geological conditions. The two methods have good consistency. Improved TRT method solves the problem of seismic source hammer excitation and detector installation, has good precision for advance geological prediction. TRT also providing reflection interface and wave velocity curve, these data are beneficial to the analysis and judgment of geological engineers. Research shows that using EH4 as the macro forecasting method, ISP,HSP and TRT as the comprehensive prediction methods, has a good geological forecasting effect in southeast Tibet double shield TBM tunnel, prediction results provide a basis for engineering construction and technical treatment.