The ground is made of clay so we excavated and did the back filling with river sand and we have laid the excavated clay around the building walls.
But I'm noticing that rain water that runs off from the building wall to ground.
I'm noticing many of the buildings have river sand filling around the building.
But is clay not a ideal choice - because absorption rate is less and it would be good for building foundation and wall?
Update
Please find some images and videos around the building.

