Abstract: As an advanced supporting structure of the tunnel safely passing through unfavorable geological areas, the pipe roof play its supporting role depending on the soil arch effect. The pipe roof spacing is closely related to the arching effect. In this paper, a method of calculating the rational spacing of pipe roof is developed by introducing rational arch axis, considering the effect of lateral earth pressure, and combining with failure conditions of soil arching. The rationality of the proposed method is verified through the case study of Fengjujiang tunnel and comparing with the result of discrete element method. Furthermore, the variation of pipe roof spacing with the location of pipe roof and the influence of pipe roof diameter and soil parameters on pipe roof spacing are analyzed. The results show that when the lateral earth pressure coefficient is low, the spacing between the hance and the side wall can be increased appropriately. However, when lateral earth pressure coefficient is high, the pipe roof spacing from vault to hance needs to be decreased appropriately. Pipe roof spacing increases linearly with the increase of pipe roof diameter and soil cohesion, and is positively correlated with the friction angles in soil. With the increase of internal friction angle, the influence of pipe roof spacing is also increasing.

Key words: pipe roof, soil arching effects, pipe roof spacing, discrete element