Study on Stability and Seepage Characteristics of Small Clear Distance Tunnel Face in Urban Rich Water Environment

Based on the double-track tunnel project of Chongqing University Town, the small clear-distance tunnel seepage system developed by ourselves is used for experimental research. Without considering the effect of excavation disturbance, the variation of water pressure and earth pressure before and after working in double-hole small clear-distance tunnels face and the prediction of tunnel intake under different static head heights were tested under different dynamic water height and static water height conditions. The results show that for the double-hole tunnel with small spacing, the lowest point is 10 m in front of the tunnel surface under different heights of the dynamic and static head. The water pressure curve presents a “V”-shaped funnel distribution along the tunnel axis. In the same position under the same water level height conditions, the dynamic head water pressure is higher than the static head. With the rise of the water level, the water pressure increases, and the earth pressure decreases. With the influence of excavation unloading, the closer the tunnel is to the face, the lower the earth pressure will be. In the middle of the tunnel, the surrounding rock in front of the tunnel has an obvious compression characteristic on the face, and the farther away from the face, the smaller the compression characteristic will be. The tunnel face is the main source of water inflow, and with the increase of static head height, the water inflow presents a non-linear growth trend.