Variation of Slurry Pipe Jacking Force in Coarse and Fine Soils

Pipe jacking force mainly consists of the penetration resistance from face pressure and the friction resistance between the pipe and surrounding soil. Jacking forces depends on following parameters: soil type, groundwater table, overburden, overcut, lubricant, stoppage, misalignment, length of drive, and intermediate jacking station (IJS). A slurry shield excavating through alluvium deposit to install a 1.5-m diameter sewer line was selected in many straight drives with similar conditions of groundwater table, overburden, overcut, and stoppage. The lubricant distributed among injection outlets along the pipeline ensures a more uniform distribution of lubricant around the jacked pipes and a more effective reduction in frictional resistance. This leaves the soil type and steering correction standing out to reduce the jacking force required. It can be concluded that the soil classification system developed in separate study helps interpreting the local variation of jacking force that is resulted from increasing penetration resistance due to either driving from coarse soil to fine soil or driving into wood log. This penetration resistance increment is recoverable when driving condition is reversed. The friction resistance increases significantly if misalignment is larger than a threshold value of 60 mm, and remains unchanged even if deviation is corrected. The misalignment effect on friction resistance is not recoverable. For large diameter pipe jacking with stabilized overcut and sufficient amounts of lubricant, the face resistance can be significant relative to the friction resistance.