Numerical model for jacking force based on pipe-soil contact characteristics

Jacking force is one of the crucial parameters to decide design of pipe structure, selection of pipe jacking meachines and design of shaft structure for jacking projects. In order to more accurately calculate the jacking force, it is assumed that the excavation tunnel is stable under mud pressure and partial contact occurs between pipe and soil of hole wall. The Persson contact model for coordinated surface is used to analyze contact angle of pipe-soil surface and distribution of contact pressure. On this basis, the formula for calculating the jacking force is deduced considering influence of friction resistance between pipe and mud concurrently. The results show that the contact angle of pipe-soil and the distribution of contact pressure are affected by the mechanical parameters of pipe and formation excavated. The contact angle approximatively tends to be constant value of 180°, and the resulting force of contact pressure is about 1.35 times the pipe weight for jacking in soft soil. When the mechanical properties of pipe and rock are close to each other, the pipe and rock tend to be point contact state. The resulting force of contact pressure is equal to the pipe weight. The jacking force measured during jacking process is consistent with that predicted by the proposed formula, and its applicability is proved.