Further investigation into the progression of soil arching under the impact of noncentered tunnel is warranted. This study addresses this need by examining trapdoor models with varying vertical and horizontal spacings between the tunnel and the trapdoor through the discrete element method. The numerical model underwent calibration utilizing data from previous experiments. The results indicated that the soil arching ratio under the impact of noncentered tunnel exhibits four distinct stages: initial soil arching, maximum soil arching, load recovery, and ultimate stage, aligning with observations unaffected by tunnel presence. The minimal disparity in stress ratio within the stationary region was observed when the vertical spacing between the tunnel and the trapdoor ranges between 150 and 200 mm. Moreover, the disturbed area on the left part of the trapdoor extended significantly beyond the trapdoor width, with notably higher disturbance height compared to the right side. When the tunnel deviated from the centerline of the trapdoor, the stress enhancement on the right side was considerably greater compared to the left. Additionally, the displacement of the trapdoor resulted in a reduction of contact force anisotropy in the soil on the side more distant from the tunnel, while increasing it on the side closer to the tunnel.

Precisely evaluating the soil pressure above parallel tunnels is of paramount importance. In this study, the deformation characteristics of soil above dual trapdoors were analyzed firstly. A novel multi-arch model for calculating the distribution of the vertical earth pressure on deep-buried parallel tunnel was then proposed based on the limit equilibrium method. The height of the dual arch zone caused by the displacement of the dual trapdoors was calculated with consideration of internal friction angle of the soil, width of the trapdoors, spacing between the dual trapdoors, and elastic modulus of the soil. By comparing with numerical simulation results and existing theoretical calculation models that do not account for the interaction of soil arching effect, it is evident that the proposed model in this study adeptly predicts the vertical stress above the trapdoor. Additionally, it captures the characteristic of upwardly convex stress distribution above the trapdoor. The analysis of parameters conducted on the theoretical calculation model showed that the depth of the trapdoor and the internal friction angle of the soil have a substantial impact, whereas the expansion coefficient exerts a negligible effect on the soil arching ratio above the trapdoor.

concrete linings in tunnels constructed by drilling and blasting such as NATM serve as a secondary support structure. However, these linings can face unexpected earth pressures if the primary support deteriorates or if ground conditions becomeunfavorable.It is crucial to determine the loosening earth pressure that allows the lining to maintain its structural integrity and prevent damage caused by this pressure. This study proposes a numerical model for simulating the trapdoor test and developinga method for calculating the loosening earth pressure. The discrete element method (DEM) was employed to describe the soil characteristics around the tunnel. Using this numerical model, a sequence of experimental trapdoor steps was simulated, and the loosening earth pressure was analyzed. Contact parameters were calibrated based on an analysis of a triaxial compression test. The reliability of the developed model was confirmed through a comparison between simulation results and laboratory test findings. The model was used tocalculate the contact force applied to the trapdoor plate and to assess the settlement of soil particles. Furthermore, the model accounted for the soil-arching effect, which effectively redistributes the load to the surrounding areas. The proposed model can be applied to analyze the tunnel's cross-sectional dimensions and design stability under various ground conditions

This paper reports several plane-strain trapdoor tests conducted to investigate the effects of reinforcement on soil arching development under localized surface loading with a loading plate width three times the trapdoor width. An analogical soil composed of aluminum rods with three different diameters was used as the backfill and Kraft paper with two different stiffness values was used as the reinforcement material. Four reinforcement arrangements were investigated: (1) no reinforcement, (2) one low stiffness reinforcement R1, (3) one high stiffness reinforcement R2, and (4) two low stiffness reinforcements R1 with a backfill layer in between. The stiffness of R2 was approximately twice that of R1; therefore, two R1 had approximately the same total stiffness as one R2. Test results indicate that the use of reinforcement minimized soil arching degradation under localized surface loading. Soil arching with reinforcement degraded more at unloading stages as compared to that at loading stages. The use of stiffer reinforcement had the advantages of more effectively minimizing soil arching degradation. As compared to one high stiffness reinforcement layer, two low stiffness reinforcement layers with a backfill layer of certain thickness in between promoted soil arching under localized surface loading. Due to different states of soil arching development with and without reinforcement, an analytical multi-stage soil arching model available in the literature was selected in this study to calculate the average vertical pressures acting on the trapdoor or on the deflected reinforcement under both the backfill self-weight and localized surface loading.

Underground excavation is usually accompanied by complex soil-structure interaction problems in practical engineering. This paper develops a novel multi-scale approach for investigating the soil arching effect through trapdoor tests. This approach adopts the finite element method (FEM) and smoothed particle hydrodynamics (SPH) method to handle the particle-rigid body interaction in the trapdoor tests, incorporating a micromechanical 3D-H model to derive the nonlinear material response required by the SPH method. The variation of the earth pressure on the trapdoor in simulations exhibits good agreement with those of the experiments. Extensive parametric analyzes are performed to assess the effects of soil height and inter-particle friction angle on the evolution of load transfer and soil deformation. Three deformation patterns are observed under different buried conditions, including the trapezoid, the triangle, and the equal settlement pattern. Results indicate that the planes of equal settlement develop progressively with the trapdoor movement and then enter the range of experimentally observed values. Additionally, three failure mechanisms are identified that correspond to the three deformation patterns. Due to the advantages of the micromechanical model, mesoscale behavior is captured. The anisotropy of stress distribution in the plastic region is found during the arching process.