They're there simply to help support the pipe, and stop it sinking into the ground beneath it.
Deep sea trenches. One tectonic plate 'subducts' under another.
Trenches
In the exhaust pipes under the truck. In the exhaust pipes under the truck.
They are called trenches.
Sea floor trenches are caused by erosion and under water volcanic occurrences
Trenches
The Ocena Trenches.
That's just silly. It can never be done.
Deep-ocean trenches are formed where seafloor tectonic plates subduct under continental plates.
Continental shelf
trenches
just under 8 feet just under 8 feet