Analysis of the influence of vehicle loads on deep underground excavation-supporting structures

The conventional equivalent thickness of soil layer method is usually utilized to simplify vehicle loads in the design of underground excavation-supporting structure, but this method does not take into account the change of rupture angle caused by vehicle loads. The change of rupture angle induces the change of the thickness of the equivalent soil layer, and the design parameters will eventually become deficient. Aiming at this problem, an improved method is presented to better solve it. Following Coulomb's earth pressure theory, the deadweight of the active wedge is calculated. Combined with the active wedge equilibrium relation, a convergence value of the rupture angle is calculated by iteration on an equation developed with differential calculus. Then, the total vehicle loads that consist of the static and dynamic vehicle loads are represented by an equivalent soil layer with a specific thickness. Based on an urban underground light-rail station, the thickness of equivalent soil layer calculated by the improved method is 0.94 m, and by the conventional method, it is 0.66 m. The influences of the vehicle loads on the underground structure as determined by a conventional method versus using the improved method are developed by numerical simulation, and some curves of lateral displacements for excavation are obtained. The results reveal that the equivalent thickness increases about 42 % after considering the change of the rupture angle. The improved method can effectively improve the design accuracy by considering the change of soil rupture angle when dealing with vehicle loads in the design of underground excavation- supporting structure.