Mechanical response of horseshoe-shaped tunnel lining to undercrossing construction of a new subway station.

• The internal force of a horseshoe tunnel is deduced by the force method principle. • Influence of the upper pilot tunnel excavation on the existing tunnel is studied. • Influence of the lower pilot tunnel excavation is studied by step-by-step unloading. • The accuracy of the proposed model is validated by comparing with other approaches. This paper proposed a calculation model for the internal force around a horseshoe tunnel based on the principle of force method. A method is proposed for computing the lateral elastic resistance of the non-circular closed ring structure. The influence of the newly constructed station of Beijing Subway Line 12 approach crossing the existing Subway Line 5 was studied with the upper and the lower pilot tunnel excavation considered. The study denotes that the maximum positive and negative bending moments of the existing tunnel increased are due to the upper pilot tunnel construction, but the influence is limited. The influence on the existing tunnel is studied by a step-by-step excavation unloading method, with each unloading width assumed to be the same as the spacing of one steel arch frame in the lower pilot tunnel excavation stage. Lastly, the construction parameters affecting the internal forces of the existing tunnel are analyzed, including the distance between the unloading surface and the existing tunnel, the unloading area, and the total excavation steps of the lower pilot tunnel. [ABSTRACT FROM AUTHOR]