A water supply tank experienced major erosion and washout of subsoils as a result of long-term settlement of the area filling.

A Controlled Low Strength Material (CLSM) was used to fill the void, which minimised the impact on the existing tank and shortened the time required to bring the tank back into operation. The CLSM was designed to allow future excavation if required (e.g. for services), whilst providing a backfill that will perform similar to the compacted gravels it is replacing.

View of erosion beneath ring beam taken from inside the tank.

Note the precast concrete piles used to support the ring beam.