Suspect the large piles of dirt are called surcharging a site.
To compact the soil, they add a significant load on top of the existing soils using the weight of the additional soils they bring in to compress the existing soils below. It only works for specific soils.
They install monitors to determine the compaction they achieve of the existing soils. It is not used a lot, I think I have seen it on sites a couple of times over the 30 years have been interested in that type of thing.
In this day and age, where time is money, most developers are not willing to spend the time waiting as it is a fairly slow process. Don't know if it also helps in the areas geological testing showed susceptible to sink holes.
http://www.cmwgeosciences.com/geotec...nt/surcharging