Analysis of Settlement of an Existing Tunnel Subjected to Undercrossing Tunneling Based on the Modified Vlasov Model

The behavior of an existing shield tunnel is significantly affected by undercrossing shield tunneling. In previous theoretical analyses, however, the effect of the interaction angle between the new and existing shield tunnels on the settlement of the existing tunnel is missing. Furthermore, in conventional methods of calculating tunnel settlement, mechanical parameters of soils, such as the shear modulus of shear layer gs and the coefficient of subgrade modulus k, are mainly determined by engineers' experience, which may lead to subjective or even biased calculation results. This paper proposes an analytical method to predict the settlement of an existing tunnel subjected to the undercrossing excavation of a new tunnel with different intersection angles. The method implements an iterative process to find reliable foundation parameters and the dimensionless parameter γ (iteration factor) in the modified Vlasov model. The robustness of the proposed method is validated by comparing the calculation results with the field measurement of two practical projects, and good agreements are obtained. The influences of the intersecting angle, the clearance distance, and the ground volume loss on the settlement and bending moment of the existing tunnel are discussed in detail. Results indicate that the intersection angle of the new and existing tunnels plays a significant role in settlement of the existing tunnel. The proposed analytical method enables engineers to predict the settlement of the existing tunnel subjected to undercrossing tunneling with different interaction angles.