Abstract
Compared with the traditional double-arch tunnel, the double-arch tunnel without middle drift has the obvious advantage of improving the construction progress. However, the surrounding rock pressure calculation method and evolution law for it is unclear. Based on a limit equilibrium analysis, a method to calculate the surrounding rock pressure is proposed with considering the sequential excavation of the two tunnels. A numerical analysis is conducted to verify the rationality of this method. The dynamic evolution and spatial distribution characteristics of surrounding rock pressure are pointed out, i.e., the vertical pressure acting on the first tunnel increases with the second tunnel being excavated, and the vertical pressure acting on the first tunnel is greater than that of the second tunnel. The excavation impact coefficient ζ and the bias coefficient η are defined to quantitatively analyze the pressure characteristics. Two key factors influencing the coefficients including the depth of the tunnel and the surrounding rock characteristic have been analyzed. The results demonstrate that both the ζ and η increase with increasing the depth of tunnel. Besides, the two coefficients increase when the friction angle increases between 30° and 40°, but decreases after exceeding 40°. The analytical results are consistent with the numerical calculation results, which can provide a reference for similar engineering projects.
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