Filling below mean sea level usually has a low density. The settling sand in standing water would form a loose skeleton leading to a low density. However, as the sand level is rising, the increased load causes reallocation of sand grains in lower layers.
As such, after dissipation of excess pore water pressure, it results in increased density.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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