Finite strain analysis of squeezing response in an elastic-brittle-plastic weak rocks considering the influence of axial stress

Abstract

When underground openings are excavated in weak rocks under a high overburden, large deformation and squeezing problems may take place. This paper generalizes the finite strain theoretical solution of Vrakas and Anagnostou (2014) for the ground squeezing response to elastic-brittle-plastic deformed rocks subjected to both the in-plane hydrostatic stress and the arbitrary axial in-situ stress. The ground behavior is analyzed based on the motion of material points in deformed configuration, thus the geometric non-linearity of rock mass is considered. Three different types of the plastic region can develop which depends on the magnitude of the axial in-situ stress, and the effects of axial in-situ stress and axial plastic flow on the squeezing response of rock mass are clarified in the case of large deformation. Comparisons among the large strain formula, the small strain theory and the numerical simulation results are made by using some examples, and the applicability of small strain method and some simplified models neglecting the axial in-situ stress is investigated. Finally, an engineering application in the severe squeezing Yacambú-Quibor tunnel in Venezuela is introduced to show the validity of the present large strain method in practical engineering. It is therefore very helpful from a practical standpoint for the preliminary design of cavities in squeezing rock mass, where the large deformation may exist and the classical small strain elasto-plastic analyses are inappropriate.