Application of Rectangular Pipe Jacking Machine in Sandy Gravel Strata

A rectangular pipe jacking machine, measuring 6.02m in width and 4.52m in height, is being used for the construction of a pedestrian underpass in Chengdu. With an invert depth of approximately 9m below the ground surface, the underpass spans a total length of 68.7m. It crosses an in‑service metro line, positioned just 3.1m above the top of the metro tunnel. Furthermore, there are about 15 municipal pipelines located between the underpass and the ground surface.

Project Background

This project marks the world’s first application of the rectangular pipe jacking machine with Earth Pressure Balance, specifically designed for construction in composite strata with shallow overburden. The geological structure of the underpass is notably complex, consisting of silty clay, a fine sand layer, and a gravel layer from top to bottom. The high water table and strong permeability increase the risk of soil disturbance, heightening the potential for collapses. The unique geographical location and complex geological structure impose stringent safety requirements, making the construction process particularly challenging. The successful implementation of the rectangular pipe jacking machine with Earth Pressure Balance, specifically designed for sandy gravel strata, sets a new precedent for using rectangular pipe jacking machines to excavate sandy gravel strata.

Pedestrian Underpass Project Route in Sichuan University, Chengdu

Tunnel after completion.

Machine is entering sandy gravel strata for construction.