Pipeline operators commonly use means of temporary crossing such as timber-mat, airbridge, and slab to reduce surface loading induced stresses in a buried pipeline at locations where a heavy vehicle crosses a buried pipeline. When a temporary crossing has a continuous contact with the soil, (e.g. timber mat, flexible slab) load distribution over the ground surface is not immediately known. Load distribution under a timber-mat or flexible slab is a function of the slab to soil stiffness ratio.  The load distribution tends to become more uniform with increasing timber-mat or slab stiffness. In this work an analytical model using beam-on-elastic-foundation has been developed and Laplace transform is utilized to find the solution and apply free-end boundary conditions. The analytical solution can be used for any arbitrary load distribution over a beam- on-elastic foundation, however in this work the solution for a point load and a uniformly distributed load were employed as these scenarios can accurately represent conventional vehicle foot-prints, while being computationally efficient. The analytical solutions are compared to finite element analysis to validate the model. The model has been programed into Microsoft excel for two different temporary crossing types, namely timber-mat and flexible slab. The end product of the program includes load distributions in form of load matrices for various load cases, each representing a different vehicle location on the slab or timber-mat to represent a moving vehicle. This model can be used in conjunction with the Canadian Energy Pipeline Association (CEPA) surface loading calculator or similar tools to analyze pipeline encroachment problems when means of temporary crossing is utilized to distribute the load more uniformly over the ground surface. This model can help the operators determine dimensions and bending stiffness of timber-mat or flexible slab to assure a desirable load distribution will be achieved. The model can also be used for structural analysis of a timber-mat or flexible slab under vehicular load.


Surface Loading Analysis: Vehicle Load Distribution Under Timber Mats and Flexible Slab

Division / Sponsors: 
Pipeline Systems Division

Paper Proceedings: https://asmedigitalcollection.asme.org/IPC/IPC2020/volume/84447

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