Surface settlement law of double-hole pipe-jacking tunnel undercrossing expressway

With the rapid urbanization process in China, there has been a significant development of urban underground spaces. The pipe-jacking method has gained popularity in various projects due to its advantages such as short construction period, adaptability to different soil conditions, and minimal excavation disturbance. This study focuses on a tunnel project involving double-hole rectangular pipe-jacking under an expressway. Utilizing FLAC software, a three-dimensional numerical model was created to analyze the impact of double-hole pipe-jacking construction on surface settlement and deformation of the expressway. The simulation results were validated by comparing them with field monitoring data. The study also investigated the impact of different construction parameters, such as excavation sequence and the angle of underpassing the expressway, on surface settlement. Additionally, the surface settlement curve at the slope bottom of the expressway exhibits asymmetric distribution and an offset center in the settlement trough. It is recommended to carry out the construction of double-hole pipe-jacking in the sequence of "big first and then small". Furthermore, when the included angle between the expressway and the jacking axis is 90 degrees, the impact on surface settlement is minimized. This research provides valuable insights for the construction of double-hole pipe-jacking underpass structures in tunnel engineering.