Swimming Hole

It appears to me that when you have to use a heavy machine to chip out solid rock for a hole for a swimming pool- once you had the hole dug, you could just fill it up with water...right?! Why do we have to pay for steel reinforcement and gunnite, inside a solid rock hole?!

The digging is alot harder than the pool company expected and they are having to haul away, rock by the truck load. Plus the machine doing the digging is like a giant jack hammer and it is VERY NOISY.
After seeing the difficulty of digging this hole and seeing the difficulty of the trenching for the geo thermal system (also in rock)...our builder reassured us that we have "built our house upon a rock"!