THREE-DIMENSIONAL NUMERICAL ANALYSIS OF EXCAVATION EFFECT ON ADJACENT DOUBLE-COMPARTMENT UTILITY TUNNEL

With the development and utilization of urban underground space, more and more basement excavations were located nearby an existing utility tunnel and have an important impact on the safety and waterproof performance of the utility tunnel. Based on a field case in Xiamen, a three-dimensional finite element analysis was conducted, using PLAXIS 3D with a HS-Small small-strain soil constitutive model, to investigate the effects of basement excavation on an adjacent double-compartment utility tunnel. The numerical results show that the deformation mechanism of an adjacent utility tunnel induced by excavation can be divided into three characteristic deformation modes, namely a translational-rotation zone, a relative torsion zone and a displacement constraint zone. Around the middle part of the basement excavation, the utility tunnel shifts towards the basement and rotates about its axis. Around the boundary of the basement excavation, the utility tunnel was subjected to relatively torsion. In a zone far from the basement, the utility tunnel was constrained by the surrounding soil and was relatively static. The cross-section of the utility tunnel located in the translational-rotation zone and the relative torsion zone was sheared towards the basement excavation. The roof of the utility tunnel displaces horizontally relative to the floor. Besides, the roof of the municipal compartment near the basement excavation and the lower part of the side wall far away from the basement excavation experience larger deformation. The distance between the utility tunnel and the basement has insignificant effect on the distribution of the three deformation characteristic zones. The closer the basement excavation is to the utility tunnel, the greater the deformation of the utility tunnel.