Formulae for frictional resistance considering mud thixotropy and pipe-soil contact characteristics

The jacking force is the crucial parameter for the design and construction of pipe jacking projects. It is controlled by the lateral frictional resistance of pipe jacking and affected by the characteristics of pipe-soil contact and pipe-mud contact. In order to calculate the frictional resistance of pipe jacking more accurately, it is assumed that the excavation tunnel is stable under mud pressure. The pipes are contacted with soil and mud concurrently. By using the Persson's contact model for coordinated surface to study the pipe-soil contact characteristics, the pipe-soil frictional resistance can be obtained by considering the contact pressure distribution. By using the cylindrical cavity expansion theory in elastic half plane to analyze the thickness of mud screen influenced by the mud pressure, the pipe-mud frictional resistance is calculated by combining the mud thixotropy with the hydromechanical model for parallel plates. And on this basis, the frictional resistance formulae for the straight line and curved pipe jacking are summarized considering the relative position of pipe and excavation tunnel, the sliding friction as the lower limit value during jacking process and the static friction as the upper limit value at restarting of pipe jacking. Compared with the data of project cases, the results show that the lower limit value by the proposed formulae is the closest to the measured one, and thus its applicability is validated.