Analysis on Surrounding Rock Pressure during Construction of Shallow Buried Bias Loess Tunnel with Small Clear Distance

In order to solve the problem of good connection of line bridge tunnel and road planning under special terrain, a variety of special forms of tunnels have emerged. As a new type of tunnel structure, small spacing tunnel can adapt to complex terrain, and thus it has been widely used in recent years. Taking an expressway as the research background, by establishing the calculation model of surrounding rock pressure of the left and right tunnels of shallow unsymmetrical pressure small clear distance tunnel, the calculation formula and applicable conditions of surrounding rock pressure during tunnel construction are derived according to relevant codes, and the sensitivity of tunnel parameters to surrounding rock pressure is studied too. The results show that: (1) The vertical pressure will increase and the lateral pressure and horizontal pressure will decrease when the back tunnel is excavated. (2) The lateral pressure coefficient of the surrounding rock outside the double tunnel is affected by the calculated friction angle of the surrounding rock, the friction Angle on both sides of the middle rock pillar and the bias slope Angle, while the lateral pressure coefficient of the surrounding rock inside the double tunnel is also affected by the buried depth and the net distance of the tunnel. (3) The vertical pressure distribution of tunnel vault is affected by the buried depth, bias angle and lateral pressure coefficient, but it is mostly affectedlt by the buried depth of tunnel. (4) The horizontal pressure of tunnel surrounding rock is affected by the lateral pressure coefficient of tunnel and the buried depth of tunnel, but the buried depth of tunnel plays a major role, the greater the buried depth, the greater the horizontal pressure of tunnel.