Abstract:

For reducing the construction risk of undersea tunnel, insuring the tunnel to smoothly pass through each weathering zone, and resolving the technical difficulties to obtain rock mechanical parameters, the dynamic back prediction model was established based on the displacement back analysis. As a comparison, an overall optimization method on elastoplastic back-analysis is briefly presented. Combining the hydrogeology exposed by advanced service tunnel, back analysis was carried out on the basis of the vault settlement and around convergence displacement by practical monitoring measurement. Then, the mechanical parameters would be obtained; that is, equivalent elastic modulus and confinement pressure coefficient of surrounding rock after primary support. Furthermore, in the similar geological conditions, boundary element method was used to normally simulate left and right main tunnels immediately after face advance and primary anchor bolt-shotcrete support. The normal calculation results could provide quantitative basis for comparison and selection of construction schemes of main tunnel, and adjustment and correction of support parameters of main tunnel. It realized the dynamic information design and construction. The analysis of engineering example indicates: it is reliable to obtain the equivalent mechanical parameters of surrounding rock by displacement back analysis. In similar geological conditions, the equivalent mechanical parameters can be used for normal calculation of main tunnels; furthermore, to forecast their deformations and failure modes, and estimate their surrounding rock stability. Displacement back analysis is a bridge which associates theoretical analysis with engineering during tunnel construction, and supplies a practical way for engineering design, construction and decision-making.

Key words: undersea tunnel, monitoring measurement, surrounding rock stability, displacement back analysis, optimization method, elastoplastic back-analysis, normal calculation-back analysis