scope:

This bulletin provides the development of simple rules for evaluating the significance of surface impacts with respect to the design requirements for buried steel pipelines that are located at shallow depths under the impact region. Useful insights gained from the existing studies on dynamic compaction are used to select appropriate formulations for evaluating the magnitude and duration of the surface impact load. The acceleration time histories of the impact load are represented by a triangular pulse. Observations made from detailed finite element analyses show that the vertical soil stress at the crown of buried pipeline located at shallow cover depths can be evaluated pseudo-statically. Existing closed-form formulations for evaluating stresses around lined circular cavities in a uniform pressure field are combined with the Boussinesq's equation to propose a modified formulation. For non-uniform pressure fields like those due to surface impacts, the proposed modification gives accurate soil stresses around the buried pipeline. The proposed formulation is verified by comparison with the results obtained from finite element analyses. A closed-form integration of the acceleration time history, facilitated by its representation as a triangular pulse, is used to develop a simple formulation for evaluating the maximum penetration depth. The time variations of the velocity and displacement at the soil surface obtained from closed-form integration are very similar in nature to those obtained by other researchers from a numerical integration of the acceleration time histories recorded in laboratory tests