Abstract: The expression of equivalent elastic resistance coefficient of surrounding rock in excavation-disturbed zone is derived based on the elastic solution of circular tunnel in infinite elastic solid and the displacements of excavation-disturbed zone and undisturbed zone. The rationality of the expression is verified through case comparison. Results reveal that the equivalent elastic resistance coefficient of surrounding rock is in a non-linear relationship with the elastic modulus of disturbed zone. With the decrease of elastic modulus and increase of Poisson’s ratio, the stiffness, lateral restraint ability and equivalent elastic resistance coefficient of rock mass will decrease. Under given excavation radius, the extension of disturbed zone would reduce the bearing capacity and equivalent elastic resistance coefficient of rock; while under given depth of disturbed zone, elastic resistance coefficient decreases with the increasing of excavation radius. The results suggest that stability of surrounding rock was affected by the combined action of disturbed zone and undisturbed zone. Taking the rock parameters of disturbed zone only in the computation will lead to overestimation of bearing capacity of surrounding rock. Therefore, equivalent elastic resistance coefficient of surrounding rock should be considered for the rational estimation of rock’s bearing capacity.

Key words: circular tunnel, surrounding rock, equivalent elastic resistance coefficient, excavation-disturbed zone, excavation radius