Numerical Modelling of Underground Water Pipelines exposed to Seismic Loading

The essential factor that must get the interest by the engineers during the primary design stage of underground pipes is understanding mechanism of damage during earthquakes. The attention during design period increased due to the increment of seismic catastrophes throughout the few past decades. Therefore, finite element procedure was used for studying the seismic performance of buried pipes. PLAXIS-2D program was using for simulating the seismic performance of buried pipes using earthquake motion of single frequency. The response of both seismic vertical displacement, and acceleration of the buried pipe were simulated. The experiments of shaking table for two models of buried pipe in dry case that surrounded with sand and gravel were compared with numerical simulation results. According to the obtained results, the amplification of seismic wave raised considerably from the buried pipe base to the pipe crown, the biggest amplification occurred in the highest point of the pipe model. It can be noticed that Plaxis-2D software provides an accurate method for the prediction of seismic behaviour of buried pipe due to the obvious compatibility between the results of experiments and numerical simulation.

A mechanical model to determine upheaval buckling of buried submarine pipelines

Thermal loads in submarine pipelines generate an axial compressive load that can force the pipeline to buckle, leading to failure if these loads are not considered in the design. Buried pipes are constraint to displacements in all directions, which leads to a high compressive load in the longitudinal axis and makes the pipes more vulnerable to buckling. If buried pipes under thermal loads do not buckle, a high-stresses state takes place when it is combined with high-pressure conditions. In this work, a simple mechanical model to determine the axial buckling load of a buried pipeline is proposed. The model is based on a simply supported beam subjected to a distributed transverse load representing the soil uplift resistance obtained from a referenced model, and an axial compressive load that represents the effective axial force and is computed according to the DNV-RP-F110. Additionally, the pipe–soil system is analyzed through a non-linear finite element model to compare the results with the analytical solution. The proposed simple mechanical model can capture the upheaval buckling behavior and provides results that are consistent with the numerical analysis, specifically for the two main parameters evaluated, namely, the initial pipe curvature and the magnitude of the transverse load.