St Albans Sinkhole – Emergency Foamed Concrete and Ground Stabilisation

Sinkholes and Dean-holes tend to be a more common occurrence when the weather turns and there is a larger volume of rainfall. Caused by poor drainage, leaking pipes and ground water, Sinkholes require a medium of stabilization urgently to prevent more damage to services or property.

The recent occurrence of a sink hole under residential buildings in St Albans required Propump to be on site the next day in order to carry out emergency works in order to stabilize the foundations and floor slab. Filling the up to 4 metre deep void Propump supplied a P445 mix at a density of 1100 KG per cubic metre in order to make the immediate area safe for further investigation.

Foamed concrete is used as void fill or reinstatement medium and can be pumped from a safe distance. This reduces the likelihood of any more subsidence due to vehicular movements in the immediate area. Propump have often found that foam concrete is specified for these jobs due to workability of the material post fill. This is because:

• 1N/mm² strength means that it can easily be re-excavated to replace/repair services
• Foamed concrete can be easily and readily core drilled to allow further investigation of the causes of a sink hole and any unseen voids below the initial collapse.
• Bonded stable structure of foamed concrete allows it to be excavated with little risk of collapse.
• Foamed concrete as a material does not move or settle post cure and as such does not need to be compacted or vibrated to create a solid non-structural load bearing surface.