Division method for deep and shallow tunnels

The earth pressure applied on the lining is affected significantly by the soil arching effect during tunnel excavation. The critical depth becomes one of basic parameters to determine the pressure of the surrounding rock when designing the tunnel structure. Based on the additional load characteristics of the surrounding rock, a user-defined elastic-plastic material subroutine (UMAT) of the constitutive model considering complex stress path of soils is complied. Three-dimensional finite element analysis of tunnel excavation is carried out by means of the secondarily-developed ABAQUS with the UMAT. The soil arching effect is studied from two aspects: the deformation law of the surrounding rock and the stress path. According to the results, a new division method for deep and shallow tunnels is proposed, which can be illustrated by the critical depth. The critical depth is determined as the depth in accordance with the vertical displacement of ceiling becoming steady when there is no supporting structure, and the depth in accordance with the maximum settlement of the surface soil above the tunnel when supporting structures exist. Compared with the critical depth determined by the code, the proposed method can reflect the macroscopic deformation law of soils. Moreover, the quantitative impact of various factors is taken into account at the same time.