Buried Flexible Pipes: Deflections and Stresses Caused by an Increase in Soil Cover—Highway Crossing

Buried flexible pipes in service are often subjected to an increase in soil cover - like a highway crossing built after the pipe has been put into service. What will be the deflections and stresses in the pipe due to this increase in soil cover? Are these deflections and stresses excessive? Academic analyses can be complex and imprecise. Complexities include traffic load impact and vehicle spacing, the slopes of the fill, and the effect of cohesion in the increased soil cover and in the highway surface pavement (asphalt or concrete). Imprecision includes compaction of sidefill soil at the sides of the pipe, non-uniformity of soil embedment and bedding among other factors. Traditional academic precision cannot be justified. Reasonable analyses are the following based on worst case causes of deflections and stresses in the pipe. These causes are stresses and strains in the embedment soil. Of course, ignoring the ring stiffness and longitudinal stiffness of the pipe is worst case. Assuming point load at the surface, W, for vehicles (construction or trucks) is worst case. Closely spaced surface live loads are worst case. Yield strength is worst case. However, steel pipe can perform in the ductile range while considering all of the mentioned worst case scenarios. This paper is a case study for a typical increase in soil cover.