Indoor model tests on the construction of vertical pipe jacking in shield tunnel

The traditional shaft construction method has a great impact on the residents' life, the environment and the surrounding traffic. With this background, the vertical pipe jacking technology has been developed rapidly. Based on the existing relevant researches, an indoor model test device for the vertical pipe jacking is designed and invented. Moreover, the influences of three factors, namely, different overburden heights, different jack lifting speeds, and whether the soil layer contains water or not, on the vertical pipe jacking construction are investigated. The changing laws of the deformation of the inner side of the shield tunnel and the vertical displacement of the ground surface due to the vertical pipe jacking construction in the shield tunnel are studied. The results show that the bending moment inside the shield tunnel presents a "W"-shaped distribution during the vertical pipe jacking process. When it is far from the center of the pipe jacking excavation, the vertical displacement of the ground surface is dominated by settlement, while near the center of pipe jacking excavation, the surface settlement decreases and presents an uplift phenomenon with the continuous jacking of the pipe. Furthermore, when the jacking speed is slow, it has a greater impact on the tunnel and the surrounding soil. When the overburden height is lower than 450 mm, with the increases of the overburden height, the settlement at measuring points in the surface settlement area increases. However, the overburden height has less effect on the displacement at measuring points in the uplift area. When the height of the covering soil increases to 500 mm, the surface uplift phenomenon disappears. The influences of the soil layer on the tunnel are more severe after adding water, which will cause the surface uplift value to increase.