Ground Stability Analysis in Non-Open-Cut Tunneling Method Using Small-Diameter Steel Pipe Piles

The non-open-cut method is used for constructing tunnels under existing roads without blocking traffic. Various non-open-cut methods use pipe roofs made of medium- and large-diameter steel pipe piles. However, the risk of ground settlement or heave is involved during the application of such piles. Therefore, research is conducted through model tests and numerical analysis on the non-open-cut method to investigate these problems using small-diameter piles. The progress of tunnel construction is divided into two repetitive steps. The first step (Stage 1) involves pulling back the pressure panel, and the second step involves propelling the precast structure (Stage 2). The behaviors of the pipe piles and ground displacement are analyzed according to the cover depth, tunnel size, existence and nonexistence of the shoe structure, and progress of tunnel construction. Small-diameter piles reduce the displacement during both stages. With a decrease in cover depth, the stress acting on the pile decreases during Stage 1 and increases during Stage 2. The presence of the shoe structure reduces the stress on the pile during both stages. The ground behavior based on the construction progress indicates that the ground settlement increases during Stage 1; however, no correlation is observed during Stage 2 at low depth.