On the frictional property of lubricants and its impact on jacking force and soil–pipe interaction of pipe-jacking

Lubricants are frequently applied in pipe-jacking, especially under difficult geological conditions or in cases of a longer alignment. The main purpose of lubricant application is to reduce the friction between pipe and soil. However, it is very difficult to quantitatively determine the real contact conditions between the two. New technology for soil–pipe interaction measurement is still scarce and requires further development. Only indirect methods are available for practical measurement of soil–pipe interaction, and engineering judgment is required for the application of those measurements. In this study, a simple test method was applied to obtain the frictional properties of the most popular lubricants in the Taiwan area. Those frictional properties were used for jacking force estimation and numerical analysis of soil–pipe interaction for linear and curved pipe-jacking. The analyses of jacking force show that reduction in jacking force is closely related to reduction in friction coefficients, and the effect of lubrication is slightly more significant in the case of curved alignment than the case of linear alignment. In addition, a study of a 400-m linear pipe-jacking case in the Taichung Science Park shows overestimation of the jacking force by an empirical formula. It reveals the reduction in pipe-soil contact area induced by over-cutting is significant for pipe-jacking in gravel formations.