Settlement Characteristics of Jacked Box Tunneling underneath a Highway Embankment

The rapid expansion of urban road systems inevitably results in engineering challenges when new road construction requires the safe crossing of existing roads. Therefore, there has been increased interest in box culvert jacking construction and specifically in the novel jacking method of box culvert shield jacking that combines the principles of box jacking and shield tunneling and is a safe approach for underpass projects. In this study, an underpass of a new road running under an existing highway in Zhengzhou, China was constructed using the box culvert shield jacking method. The objectives of the study were to introduce the novel construction and to investigate the development of the settlement characteristics of the existing highway. A numerical analysis was used to establish a three-dimensional numerical model, which was validated by field measurements. The results showed that (1) the novel box jacking method is safe, feasible, and successful; (2) along the jacking direction, the highway settlement gradually decreased from the entrance (south) to the exit (north); (3) during the process of jacking, the settlement behavior of the existing highway underwent three stages, namely slow growth, rapid growth, and a steady stage. A parametric study included investigations of the length of the shield and the lag distance between the central soil and the shield face. These results provide information for similar projects and help to improve box jacking construction. (C) 2019 American Society of Civil Engineers.