Investigation of the Stress and Strain Distribution in the Surrounding Soil of a Tunnel Induced by the Double-Heading at Bottom Method

The tunneling process in water-rich silty fine sand stratum often faces challenges such as arch collapse due to the instability of the initial support arch foot. The present study focuses on the Taoshuping 3# inclined shaft section, modifies the two-side heading method (THM), and introduces the double-heading at bottom method (DBM). Field monitoring and numerical simulations are employed to investigate the formation pressure, deformation evolution, and the advantages of the construction scheme using the loosened zone and stress distribution features. The obtained results show that DBM exhibits a maximu m settlement during arch excavation, constituting approximately 36% of the total settlement, with a total value of 222.21 mm. Furthermore, the plastic zone induced by DBM ranges from 1.23 to 2 times the tunnel diameter, with vertical and horizontal surrounding soil pressures of 140.72 kPa and 46.25 kPa, respectively. DBM is markedly superior to THM. This approach reduces the formation of wedge-shaped shear bodies caused by excessive stress at the sidewalls in THM excavation. Even with tunnel excavation support, the surrounding soil maintains an arch effect, validated through calculations using Protodyakonovco theory and Terzaghi theory, verifying the efficiency of the support structure design.