Deformation control of surrounding rock of rectangular pipe-jacking tunnels considering key construction parameters

In densely populated urban areas, large rectangular pipe jacking projects are becoming increasingly popular. One of the most difficult aspects of the pipe jacking construction is to control the deformation of the surrounding rock. The impacts of four major construction parameters such as earth chamber pressure, pipe-soil friction, grouting pressure and equivalent layer on three-dimensional formation deformation are explored using the numerical simulation and field monitoring on a large section rectangular pipe jacking project in Tianjin. The findings demonstrate that: (1) The earth chamber pressure and grouting pressure are the primary causes for the uplift of the surrounding rock mass, and the gap-filling degree between the pipe section and the surrounding soil is the primary cause for the settlement of the surrounding rock mass. (2) The major causes for the axial horizontal displacement of the surrounding rock soil are the pipe-soil friction and earth chamber pressure. The surrounding rock soil is exposed to the same shear and extrusion as the jacking direction due to the pipe-soil friction and earth chamber pressure. (3) The surrounding rock mass moves to the outside of the tunnel due to the grouting pressure and pipe-soil friction, resulting in transverse and horizontal displacements. The surrounding rock mass moves to the inside of the tunnel due to the gap-filling degree between the pipe section and the surrounding soil, resulting in transverse horizontal displacement. The findings of this study have significant implications for the formation deformation control of large-section rectangular pipe jacking construction.