Numerical evaluation of a deeply buried pipe testing facility

Abstract

A new facility for testing pipes under deep burial has been developed. However, before the facility was commissioned, the influence of the loading scheme and boundary conditions on the pipe behaviour was investigated so that the most appropriate experimental setup could be developed. Two- and three-dimensional finite element analyses were used to assess the impact of the top and side boundary conditions on both flexible and rigid pipes with varying diameters. The vertical overburden pressures expected in the field are simulated using actuators applying vertical forces to two steel grillages. The numerical results show that the use of two independent grillages on the surface produced a more uniformly distributed ‘overburden’ pressure, a novel approach that performs significantly better than previous loading systems. Proximity of the test facility’s walls to the pipes was also investigated and found to have less than a 0.2% impact on pipe response when compared to simulations of field geometries. Results examining five different approaches to reducing the effect of sidewall friction were compared to the case of zero friction (i.e. the field case), and it was found that while lubricating the wall to create a friction angle of 5° over the full height produced the most accurate results, lubrication of only the top 2.5 m of the wall also produces thrust forces and bending moments within 10% of values from the zero-friction case. Finally, the effect of the position of the pipe within the test cell was investigated, where pipe testing with 0.3 m of bedding is expected to produce results like those for pipes close to rock foundations in the field. These results are already being used to inform testing procedures using this unique facility.