An improved method to calculate the vertical earth pressure for deep shield tunnel in Shanghai soil layers

Previous studies on field monitoring data indicate that vertical earth pressure would be overestimated by the Terzaghi theory for a deeply buried shield tunnel, which is widely adopted in tunnel design. A kinematic mechanical model was proposed to evaluate its influence on vertical earth pressure and implementation into the finite element program in this paper. To investigate the vertical earth pressure, a numerical study using the commercial software of PLAXIS was conducted on the vertical earth pressure distribution on a single shield tunnel, considering different tunnel diameters and burial depths in sandy and clay layers, such as Shanghai soil strata. Based on finite element model results, the existing problems such as soil displacement around tunnel, earth pressure distribution, collapsed soil mass width and sliding friction in the Terzaghi loosening earth pressure formula for a sand layer were discussed. Then, a feasible calculation method for vertical earth pressure on the tunnel lining was proposed. Through comparisons between calculated results and field measurements, the improved formulas were verified, providing a reference for future designs of deep underground structures in Shanghai Soil Layers.