I wish to build an underground water holding tank. It will be 12’ wide by 12’ long by 10’ high. It will be constructed out of reinforced concrete. My figures show the box to be 1440 cubic feet, 10,771.2 gallons, and 89,827 Lbs. or 44.91 tons. The container will be buried in the ground with a concrete top to it. My question is, how thick will the walls need to be, and the floor. What would the pressure be on the walls? I am not sure of the cost of construction, or just to bury a tanker truck. Thanks for your answers.