An underground (U/G) tank is a container that can be used for storing a liquid without appreciable loss by leakage through its walls or base. Various underground water tanks are U/G components of a sewage treatment plant, swimming pools, sumps, oily water sewers, sulfur pits, manholes and catch basins.
Water tanks are used to provide storage of water for use in a number of applications. The structural design of a water tank includes design parameters such as concrete grade, reinforcement grade, soil parameters, water table and edge support conditions of the tank walls. The tank slab and wall thicknesses mainly are decided based on the edge shears and bending moments. Generally, reinforcement consists of 2 orthogonal layers on each face with adequate concrete covers. Crack control check is a necessary check in u/g tank design. Testing for leakage is an obligatory test is u/g tank design.
In general, underground water tanks are used for various purposes such as storage of potable drinking water, wastewater, rainwater collection, housing underground tanks, and vessels etc. The outer walls generally are required to retain outer soil and groundwater and sometimes a surcharge load that may come from construction vehicles moving in the vicinity of u/g tank.
Filling a newly constructed underground water tank while backfilling on the outer side reduces the differential pressure between the outside and the inside of the tank, thus, minimizing