Close construction effect and lining behavior during tunnel excavation with an elliptical cross-section

Abstract Tunnel excavations near existing structures impose additional loads on the nearby structures and influence the stress-strain regime of the soils. In the present study, the ground response during the close construction of tunnels and the structural behavior of a segmental lining with an elliptical-shaped cross-section were investigated. The effect of nearby structures and the influence distance for a nearby excavation were discussed in terms of the changes in volume loss around the tunnel, the horizontal soil deformation, and the distribution of internal forces. Furthermore, the structural behavior of the lining was tested by showing the capacity of the reinforced concrete section and by considering the crack development in the elliptical-shaped segment. The results demonstrated that the influence distance of the elliptical-shaped tunnel excavated in coarse-grain soils was approximately four times the minor diameter of the tunnel and that the axial force increased slightly in the part of the lining close to the existing structure when the pillar width was increased. Furthermore, it was demonstrated that crack development is an important issue in tunnels with an elliptical cross-section near the spring line; and therefore, a safe zone corresponding to the onset of several cracks with an allowable width and average crack spacing was recommended.