Fluctuating loads. Similar to vibrations, fluctuating loads can also cause long-term foundation
settlement. An example would be an oil storage tank that is filled and emptied many times over
its life. If loose sand supports the oil tank foundation, then the loading-unloading cycles could
slowly densify the sand, resulting in long-term settlement. It has been suggested that for structures
subjected to slight fluctuating loads, the settlement of footings on sand 30 years after
construction might be as much as 1.5 times the immediate post-construction settlement, while
for heavy fluctuating loads, the settlement might be as much as 2.5 times the immediate postconstruction
settlement (Burland and Burbidge, 1985). Actual values of post-construction settlement
would be dependent on the number of loading-unloading cycles, the magnitude of the fluctuating
load, and the density of the sand (loose versus dense).