Abstract
Shield excavation in a proximity to existing tunnels inevitably causes deformation and stress change of the adjacent tunnels. Based on the project of new metro line in Beijing where the shield tunnel was constructed under existing tunnel, a modified equivalent stiffness model for the existing tunnel is proposed. Based on this, a three-dimensional finite element is established, and subsequently the proposed modified equivalent stiffness model and the previous model are implemented into the finite element model (FEM), respectively, and then the effectiveness of it is verified through comparison with the field measurements. The results indicate that the modified equivalent stiffness model has excellent agreement with the monitoring value. The impacts of key parameters including undercrossing angle, vertical spacing, and soil parameters on the crown settlement of the existing tunnel are investigated. The maximum settlement of the existing tunnel crown decreases as the undercrossing angle increases. The decease of vertical spacing between the newly constructed tunnel and the existing tunnel leads to an increase of the peak value of crown settlement. As for the soil parameters, friction angle φ is the dominant parameter affecting crown settlement of the existing tunnel whereas the cohesion c is least influential. During the process of route selection, it is suggested to keep the vertical spacing between new tunnel and the existing tunnel greater than the external diameter of the new metro tunnel. For the situation of undercrossing an existing tunnel within an extremely small clearance, it is recommended to strengthen the soil as necessary.
Highlights
With the advancement of China’s urbanization, the utilization rate of urban underground space continues to increase
E shield lining composed of segments, bolts, and rubber gaskets is not a continuous homogeneous body [4]
(1) Segmentjoint model: beam-spring model was proposed by Nishino et al [5]; shield tunnel as a cylinder could be represented by a simple beam model on an elastic foundation
Summary
With the advancement of China’s urbanization, the utilization rate of urban underground space continues to increase. E three-dimensional skeleton model [8,9,10] uses shell elements or solid elements to simulate the tube segments and considers the restraint effects between the tube segments used entities) by spring or contact forces This model was used to simulate the tension, compression, shear, and rotation effects of the joints. Liao discussed the influence range of the circular seam to modify the equivalent continuity model, but the value of which was not given; Xu [13] discussed the influence coefficient of the annular seam based on two situations where the influence range of the annular seam is within the bolt length and beyond the bolt length; Yu et al [8] took the influence of the lateral stiffness into consideration and assumed that the tunnel lining presents approximate “elliptical” deformation under the surrounding load and proposed a more effective longitudinal equivalent continuity model for shield tunnels. Parametric analysis was carried out based on the proposed modified model, and the recommended selection criteria of undercrossed angles and vertical spacing between new metro tunnel and existing line is given
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