The cistern is a circular space with a radius of 11’ and a height of 14’ surrounded by walls made of packed tires. It has a total capacity of 42,500 gallons. The use of a circular shape creates a geometrically stable shape where no buttressing is needed. In addition, it allows to avoid the presence of sharp corners where stresses would accumulate in the event of an earthquake, thus creating weak spots in the structure.

Tires are filled with the earth taken out during the excavation stage, and non-biodegradable waste. The tires are stacked in a running-bond pattern to maximize interlocking between courses. Additionally, horizontal rebars are laid between two courses about halfway up the wall to stiffen it against lateral forces during the construction stage. An 8” deep concrete bond beam is poured on top of the last course of tires in order to tie the whole structure together.

The cistern space is topped by a 6” deep concrete slab supported by beams resting on the bond beam and concrete columns founded on the cistern floor. Cistern walls are covered with concrete to provide a waterproof barrier.

The first course of tires of the cistern circular wall is filled with gravel to provide a solid footing for the wall while preventing any water infiltration via capillary action. Similarly, the 12” deep concrete cistern slab is poured on a 6” deep layer of gravel.

The cistern collection area is located at the Northeast corner of the building, where rainwater is gathered and filtered before entering the cistern. The cistern presents 2 different overflow systems for redundancy purposes.

Regarding ground drainage strategy, given the field slope, rainwater is only likely to accumulate along the North edge of the building. Thus, vertical PVC pipes are installed along the cistern wall in this area to lead any potential water to gravel trenches located beneath the cistern slab. These trenches are located below the 6” deep layer of gravel mentioned above and lead to a South drain tile evacuating the water below the cistern.