1-g shaking table tests of precast horseshoe segmental tunnel: Experimental design, dynamic properties, deformation mode and damage pattern

A novel precast horseshoe segmental tunnel (PHST) structure was applied in the construction of the west extending project of Beijing Subway Line 6. The seismic performance of the PHST was one of the critical difficulties for the engineering project. A series of investigations were conducted to deal with the problem, including the 1-g shaking table model tests of the PHST buried in sand. In the present study, the experimental setup, construction of the PHST model (tube), dynamic properties of the soil-tube system, deformation mode and damage patterns of the tube were introduced. The preliminary results show that the tube had a very slight influence on the dynamic properties of the soil-tube system, which was consistent with the traditional learning. Under seismic motions with the precautionary intensity of the prototype site, the dynamic properties of the soiltube system were not varied. The seismic responses of the tube were within the linear range. With the increasing seismic intensity, the predominant frequencies of the soil-tube system were firstly decreasing and then tended to be rather steady; meanwhile, the viscous damping ratio was firstly increasing and then rather steady. Under the excitations of the rare seismic motions, the non-linear responses of the tube were observed. The connection regions were damaged and tended to failures. Under the effects of the very rare motions, the thorough failures were observed at the connections. The tube was developed as a multi-hinge mechanism. The damage patterns at the connections were flexural damage and shear slide between segments. After the actions of strong motions, the tube kept horizontally expanding and vertically shrinking.