Soil pressures at top of large-diameter buried steel pipes and their design model

The previous research results of soil pressures at the top of buried steel pipes are mostly based on the small-diameter pipes, which are not fully suitable for large-diameter pipes. Here a numerical investigation is conducted on the soil pressures from the aspects of pipe diameter, diameter-thickness ratio and cover depth, and it is furtherly compared with the traditional design models. The influence parameters on the soil pressure are discussed. A new design model for soil pressures, basin model, is proposed. Wherein, the distribution of the soil pressures is described as "straight line + parabola", and the load calculation adopts the "Marston + pleura" according to the pipe diameter and cover depth. Furthermore, the applicability of the basin model is studied. The results show that the basic form of the soil pressures is the "inverted basin" distribution for large-diameter pipes, while the soil pressures are a parabolic distribution for small-diameter pipes. The diameter-thickness ratio and cover depth have significant influences on the soil pressures, but the soil pressures change very little after the diameter-thickness ratio is greater than 200. The increase of the elastic modulus and Poisson's ratio of backfill and roughness of trench interface, and the decrease of trench width can slightly reduce the soil pressures. The prism and Marston load are too large at high cover depth and small at low cover depth, respectively, which have poor accuracy and adaptability. The basin model is in good agreement with the finite element results, with high calculation accuracy and strong adaptability. It can provide a reference for the structural design of large-diameter buried steel pipes.