Analysis of longitudinal deformation profile in city-gate shaped tunnel using top heading and bench excavation method

The longitudinal deformation profile(LDP) is important in determining the deformation magnitude of tunnel wall as a function of distance to tunnel face.But the widely used empirical equations were derived from numerical analysis of fullface excavation of a tunnel with circular cross-section.It is not clear if the equations can still be used for city-gate shaped tunnel under top heading and bench excavation.Therefore,the LDP for top heading and bench excavation is analyzed by FLAC3D.The difference of LDP between full face and top heading and bench excavation is investigated by FLAC3D under different geo-mechanical properties of surrounding rock and in-situ stress conditions.Finally,the method on determining the LDP and its empirical equation are suggested for large tunnel using top heading and bench excavation and the equation is verified against measured data of the upper side walls at a diversion tunnel of Zipingpu project.The results show that there is similar shape for LDP curves between full face and top heading and bench excavation,but the displacement ratio at face is obvious different between them;the LDP for side wall does not vary obviously with the varied horizontal stress when the ratio of horizontal to vertical initial stress is lager than 1.0;the LDP for city-gate shaped tunnel under top heading and bench excavation can be formulated in virtue of the proposed empirical equation and numerical analysis with plain strain model,and it is verified against measured data well.The empirical equation can be easily and reliably applied to deformation analysis,and the total deformation magnitude for large tunnel can be predicted well with the monitored data.