Simple Equations for Estimating the Large Convergence and the Longitudinal Displacement Profile of a Tunnel.

This paper presents a modified relationship between small and large strain convergence by applying a small (residual) dilation angle, which behaves accurately for rock mass with the strain-softening behavior and complex dilatancy model. The modified relationship extends its applicability to a more general two- and three-dimensional excavation problems than previous study, irrespective of the constitutive behavior and rock dilatancy. On this basis, the longitudinal displacement profile (LDP) considering finite-strain is proposed, which can be corrected simply from the small strain analysis or obtained according to the actual parameters related to large deformation. The capability of the finite-strain LDP for estimating large convergences during tunnel advancement is verified by several comparisons with the existing numerical simulation and theoretical analysis results. The developed finite-strain LDP is promising to improve the convergence − confinement method when it applied to the rock-support interaction analysis in problems involving large deformation. The applicability of the displacement-release coefficient obtained from the small strain analysis for quantifying the stress relief to squeezing ground conditions is also investigated. Highlights: A relationship between small and large strain convergence is modified to accurately calculate large convergences from small strain analysis. Two equivalent formulas for the longitudinal displacement profile in squeezing ground considering finite strain are proposed. The applicability of displacement-release coefficient by small strain analysis for quantifying the stress relief to squeezing ground is obtained. [ABSTRACT FROM AUTHOR]