Effects of Lubricants in Over-cutting Area of Pipe Roof Method on Reducing Surface Settlement

The pipe roof method, one of tunneling technique, has been used over the last few decades to reduce the influence on the surrounding construction. The function of pipe roof method is to minimize ground surface settlement and promote tunnel stability. In this method, several steel pipes are jacked around the main tunnel by using slurry pipe jacking before main tunnel excavation. Ground displacement is an unavoidable problem in the construction of a tunnel and underground spaces near the earth surface. When the steel pipe is jacked, over-cutting area must be formed to be lower the friction between the ground and the pipe, and this void is immediately filled with lubricants. Due to the low stiffness lubricants in the void space, it causes displacement above the steel pipe and leads to the surface settlement. Therefore, stiffness or Young’s modulus of lubricants are significant to minimize the effects on the surface settlement. To study the effects of lubricants on reducing the settlement, FLAC3D was used for numerical modeling by introducing different strength of lubricants in the tail-void. The results showed that by increasing Young’s modulus of lubricant, the surface displacement is effectively reduced. Additionally, the simulation results are agreed with field measurement data.