The existing models for the pore pressure and internal stresses within the pipeline under wave loading have mainly based on the assumption of no-slip boundary condition at the interface between pipeline and soil particles. In this paper, soil–pipeline contact effects and inertial forces are considered in the new model. A comprehensive comparison between the experimental data available and the present model is performed and showing good agreements. Based on the numerical results, it is found that soil–pipeline contact effects significantly affect the internal stresses. The maximum difference of internal normal stress can reach 50 times of p0. On the other hand, inclusion of inertial terms will only affect the pore pressure acting on the pipeline. Numerical examples also conclude that the difference of internal normal stresses between the present model (with contact effects and inertial terms) and previous work (without contact effects and inertial terms) increases as the depth (s) of the trench layer decreases, but as the width of the trench layer (ℓ) increases. Finally, we compare three different types of trench shapes, rectangle, trapezoid and triangle trench layers, and found that triangle trench layer will reduce the pore pressure, but increase the internal stresses.