Abstract：For the design of support system of tunnel，the convergence-confinement method is a simplified analysis theory. Obviously，the confinement loss used by the theory is an important influence factor. For analyzing the influence of the confinement loss，the deformation measurements widely used in tunneling engineering are investigated；and the advancing effect function is particularly proposed to examine the alterations of deformation and stresses of rock mass around tunnel. The back calculation procedure is a technique proposed to assess the redistribution of the confinement loss. The case study of Baguashan tunnel in Taiwan is taken account of the advancing effect during construction. According to the obtained results and the comparison between numerical calculation and theoretical analysis，it is shown that：(1) the relationship between deformation measurements and confinement loss can be described by the proposed advancing effect function；(2) the parametric study of advancing effect function is examined；(3) the equations proposed for the confinement loss can be used to estimate the pre-convergence due to excavation；(4) the back calculation procedure is also proposed to understand the redistribution trend of confinement loss；and (5) the results obtained by the three-dimensional finite element analysis and the advancing effect function respectively are approximately coincident.
