What is an "Expansive Soil"?
Expansive soils contain minerals such as smectite clays that are capable of absorbing water. When they absorb water, they increase in volume. The more water they absorb, the more their volume increases. Expansions of ten percent or more are not uncommon. This change in volume can exert enough force on a building or other structure to cause damage.
Geology, Expansive Soil and Expansive Clay, 2019
It is the water that causes the soil to expand. Potholes on asphalt roads are caused by the expansion and contraction of the soil underneath them. When water causes the soil to expand it pushes the asphalt upward. When the soil dries it contracts and the asphalt makes a pothole.
However this was portrayed in the Quran 1400 years before it was discovered.
[Quran 41:39] And of His signs is that you see the land still. But when We send down water upon it, it shakes and rises. Surely, He Who revived it will revive the dead. He is Able to do all things.
"Rabua in Arabic رَبْوَة " means high ground. Its verb "Yarbu يَربُو " means rise higher. In this verse "Rabat رَبَتْ" means rose higher for females (it is also found in Quran 13:17 meaning float or rise to the top of water). In this verse water causes the soil to shake and rise upward.
How could an illiterate man who lived 1400 years ago have known that water causes soil to expand upward?