Deformation characteristics and instability mechanism of transportation hub under downward traversal conditions of the double-track super-large diameter shield tunnel

To investigate the deformation characteristics and instability mechanism of the transportation hub under downward traversal conditions of the double-track super-large diameter shield tunnel, take the example of Beijing East Sixth Ring Road into the ground reconstruction project. Using the field experimental monitoring method and numerical simulation method, after verifying the accuracy of the model, this manuscript begins to unfold the analysis. The results show that, without any deformation prevention and control measures, The basement raft of the underground structure of the transportation hub will produce a deformation difference of 18 ​mm, and the tensile stress is more than 1.43 ​MPa, the inhomogeneous deformation and structural cracking will lead to structural instability and groundwater surges, which seriously affects the safe operation of the transportation hub station. When control measures are taken, the deformation and stress of the base raft slab of the underground structure of the transportation hub are within the prescribed limits, which can ensure the safe operation of the station. The displacement of the base slab of the underground structure in the horizontal direction of the cross-section is all pointing to the east, and the overall trend is to shift from the first tunnel to the backward tunnel. The horizontal displacement of the base slab in the direction of the tunnel axis all points to the beginning of the crossing, and the displacement of the slab in the vertical direction is distributed as "rising in the middle and sinking in the surroundings". For a two-lane super-large diameter shield tunnel penetrating an underground structure, there are two mechanical effects: unloading rebound and perimeter rock pressure. The above deformation characteristics are the superposition effect produced by the two, and this fine assessment of the deformation of the raft foundation provides a scientific basis for formulating the deformation control countermeasures of the crossing project. At the same time, it makes up for the blank of the double-track super-large diameter shield tunnel down through the transportation hub project.