Earth pressure and stability of deep arch tunnel with straight wall in cohesive strata

The limit analysis method is adopted to study deep arch tunnel with straight wall in cohesive strata based on the shear failure theory. Firstly, a theoretical model for ruptured zone in the deep arch tunnel is established based on loading tests. And then a formula for lateral pressure is proposed considering the effect of two sphenoid rupture surfaces beside tunnel sidewalls. Secondly, the approximate solutions to the lateral pressure and the vertical earth pressure are derived. The criteria for the quantitative stability of the deep arch tunnel without supports are developed, and the approximate ultimate load on the ground can be calculated according to the stability of the shear wedge beside the tunnel sidewalls. Finally, the safety factor of the deep tunnel is defined based on the limit analysis method, and the influencing factors are analyzed. The results show that the proposed model for ruptured zone and the solution to the ultimate load are close to the test results. Compared with the traditional theoretical value, the calculated vertical and lateral earth pressure is much smaller according to the proposed formula. The interaction theory between lateral pressure and vertical pressure on arch tunnels is proposed in the good strata. The smaller the vertical earth pressure is, the greater the lateral pressure is, and the greater the lateral pressure or the lateral pressure coefficient is, the smaller the vertical earth pressure is in the limit state. The safety factor of stability increases with increasing the cohesive force and internal friction angle, and it decreases with increasing the span and height of the tunnel. The cohesive force and tunnel span have larger influences on the safety factor of stability than the internal friction angle and the tunnel height respectively. However, the greater buried depth has smaller influences on the stability safety factor of the deep tunnel.