Long rectangular box jacking project: A case study

Rectangular pipe jacking or box jacking has become more popular in municipal applications because of its better adaptability to shallow overburdens and its higher structural section utilization than the conventional circular pipe jacking. This case study presents a utility tunnel constructed by using rectangular box jacking in Suzhou, China. The utility tunnel, which has a cross section of 9.1 m in width and 5.5 m in height, was jacked 233.6 m, which is the longest known single jacking length of a rectangular box jacking project in China. The box jacking mainly passed through a silty sand layer with high groundwater levels with a minimum depth of cover of only 3.5 m underneath the Yuanhetang River. In this zone, the structures on the surface are sensitive to external disturbance, thus increasing the challenges of construction. A series of measures were taken during the jacking process, and the project was successfully completed. This paper provides an overview of this project and introduces key techniques in the construction of working shafts as well as in the installation and retrieval of the box jacking machine. In addition, the use of lubrication to reduce friction resistance, navigation and application of an anti-buoyancy slab under the Yuanhetang River, and analyses of soil deformation caused by box jacking are described.