Abstract
Aiming at studying the harm caused by sudden ground loadings on existing shield tunnels, a indoor scaled model test with a geometric similarity ratio of 1:15.5 was adopted. Considering the influencing factors such as ground loading, burial depth of the shield tunnel, loading position and soil properties, tunnel convergence deformation, tunnel settlement and deep settlement of soil caused by sudden ground loadings are studied. A three-dimensional finite element simulation is carried out using the Midas software, and deep settlement of soil is calculated by a theoretical method. The purpose of this model test is to further understand the influence of ground surcharges on shield tunnel deformation. The results show that the greater the ground surcharge, the greater the settlement and vertical convergence deformation of the shield tunnel; The further away from the ground surcharge, the smaller the settlement, vertical convergence deformation and lateral convergence deformation of the tunnel. When the pile load size is constant, the greater the burial depth of the tunnel, the smaller the vertical convergence deformation and settlement of the tunnel; the maximum value of deep settlement of the soil always remains at the closest point to the ground surcharge; compared with the use of dry sand, the vertical convergence deformation and settlement of the tunnel are significantly reduced when using wet sand. Both the theoretical calculation results and the numerical simulation results are in good agreement with the indoor model test results.
Highlights
The indoor scaled model test method, supplemented by a threedimensional finite element simulation and theoretical calculation method, are used to study the lateral and vertical convergence deformation, tunnel settlement and deep soil settlement of an existing shield tunnel caused by a sudden ground surcharge on the ground, and to analyze the laws that influence ground surcharge, tunnel burial depth, ground surcharge position and soil properties
When the excess pore water pressure rises in case of sudden ground surcharge, the effective stress of the soil decreases, and the sand is in a flowing state, which leads to the reduction of additional load on the tunnel, resulting in the reduction of settlement and convergence deformation of the tunnel; (2) As shown in Figures 27 and 28, under the action of ground surcharge, due to the different nature of the soil, the stress σ contours are flat when the soil is wet sand, and the stress σ decreases rapidly with the increase of depth Z
(3) In the finite element simulation, the segments are continuous without considering the bolts and joints, which is different from the tunnel model used in the indoor model test
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Scholars at home and abroad have done a lot of research on the influence of ground surcharges on existing shield tunnels, including full-scale model tests [10], scaled model tests [11,12,13], field measurements [14,15], finite element simulations [14], theoretical calculations [16,17,18,19], etc. The indoor scaled model test method, supplemented by a threedimensional finite element simulation and theoretical calculation method, are used to study the lateral and vertical convergence deformation, tunnel settlement and deep soil settlement of an existing shield tunnel caused by a sudden ground surcharge on the ground, and to analyze the laws that influence ground surcharge, tunnel burial depth, ground surcharge position and soil properties. The finite element simulation results and theoretical calculation results are compared with the indoor model test results
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