Ground settlement caused by pipe-roof pre-construction method: Effect of the sequence of jacking pipe groups

Based on the Taiyuan Railway Station underpass tunnel project, the influence of construction process of closed pipe-roof pre-construction structures on the ground settlement was investigated. Numerical simulations were used firstly to analyze the ground settlement characteristics caused by three types of different jacking pipe sequences, i. e., from top to bottom, simultaneous construction bottom and top, and bottom to top with nine cases. Numerical simulation results show that the top-down jacking pipe sequence caused the least amount of ground settlement at 12 mm. The largest amount of ground settlement of 25 mm was caused by using the bottom-up jacking pipe sequence. The numerical simulation results were validated by large scale model tests. The results of the model tests agree with the numerical simulation results, with the top-down jacking pipe sequence causing the least ground settlement and the bottom-up jacking pipe sequence causing the most ground settlement. Based on numerical simulation and model tests results, the reasonable jacking pipe sequence was successfully applied in the north tunnel of Taiyuan Railway Station to meet the settlement requirements. The results of the research show that micro soil arches are formed between adjacent jacked pipes in the jacking pipe construction. The micro soil arches between adjacent pipes above the tunnel combine into a large pipe soil arch structure, which can reduce the ground settlement caused by the jacking pipe under the tunnel and on both sides. Therefore, the sequence of jacking pipe considering a pipe soil arch structure can reduce the ground settlement caused by the jacking pipe.