Torsional Deformation of Existing Tunnels Induced by Obliquely Undercrossing Shield Tunneling
摘要
To investigate the deformation effects of obliquely undercrossing shield tunneling on existing tunnels, a three-dimensional finite element model was established based on the Nanjing Metro Line 11 project, which obliquely undercrosses the existing Line 3. The model simulated the shield tunneling process and analyzed the influence of overlapping angle, net distance, and reinforced steel rings on the torsional effect of the existing tunnel. The results show that obliquely undercrossing shield construction induces torsional deformation in the existing tunnel, with stronger torsional effects observed in the proximity zone compared to distal regions. Increasing the overlapping angle weakens the torsional effect. When the overlapping angle exceeds 80°, the rotation index decreases below 1.0 × 10–4. Increasing the net distance from 2.6 m to 6.6 m reduces the maximum rotation index of the left line from 2.58 × 10–4 to 2.12 × 10–4 and that of the right line from 2.83 × 10–4 to 2.18 × 10–4. Reinforced steel rings influence the torsional effect of the existing tunnel. Under tight integration between the I-beams and lining, using No. 32c reinforced I-beams reduces the maximum rotation index of the existing tunnel from 2.40 × 10–4 without reinforcement to 2.05 × 10–4, and the maximum additional torque of the lining decreases from 4170.5 kN·m without reinforcement to 3469.5 kN·m. In practical engineering, increased attention should be paid to areas outside the projection zone of the new tunnel onto the existing tunnel, as these regions are prone to stress concentration. Similar oblique undercrossing projects can benefit from the insights provided.