Use of soilbags to protect flexible pipes against repeated load effects

Abstract

An investigation was made of the over-trench bridging effect provided by soilbags to reduce the pressure on, and vertical and horizontal diametral change (VDC and HDC) of, buried flexible pipes, along with reductions in trench surface settlement (TSS). Full-scale tests examined the effects of burial depth, soilbag width, number of soilbag layers and distance between layers in trenches with 250-mm diameter pipes subjected to 150 surface loading cycles that simulated vehicular traffic. TSS reduced most when a soilbag was nearest the surface, while positioning a soilbag over the pipe's crown best protected the pipe. The soilbag's width must exceed 1.2 times the loading surface diameter/width to prevent unhelpful downward (punching) movement of soilbags into the trench backfill. Increasing soilbag width beyond 1.6–2 times that diameter/width or using more than two (sometimes three) soilbag layers, delivers diminishing returns. Using one to four soilbag layers, TSS, VDC and pipe pressure reduce to 45-15%, 70-15% and 75-25% of the unreinforced values, respectively, though the improvement rates diminish with increasing layers. Overall, TSS and pipe protection are similarly sensitive to the positioning of two layers of soilbags, while the spacing between the layers has the opposite effect.