The soil expands and contracts so bad roads don’t last long in that part of Texas.
Yes, lovely clay soil. Been here 40 years, it was the first time for a sinkhole
“Some repairs will also include installation of impermeable layers of soil alongside the road to keep water from penetrating that road base and causing the soil to expand. “
It was built on clay so you would assume that road slopes are also clay. Clay also acts as an impermeable soil type to prevent water from migrating. In this particular case it seems to me that the subsurface clay is already saturated and the removal of 5 feet of sub-base should cure the issue of heaving or swelling.
I would wonder why they are not putting in a sub-drain system to collect water and move it out of the newly placed sub-base should any water get through the clay slopes/shoulders.