When a crown hole suddenly opened in a garden in Kent due to a collapsed WWII tunnel, Propump Engineering’s foamed concrete came to the rescue, ensuring the homeowners and their home was not at any further risk.

At the house in Westerham, the homeowners were alarmed when the crown hole appeared a metre from their property which led to their insurance company involving engineering firm Peter Brett Associates to sort out the hazard.

“When we surveyed the site, we found that the crown hole was the result of a collapsed WWII tunnel that connected a country house to an air raid shelter,” commented Stuart Chandler, Peter Brett Associates. “Whilst the facility was abandoned many years ago and the country house extended, the tunnel and vault still remained, hidden from view for more than 60 years.”

With the hole having potential to undermine the foundations of the house, it was paramount that a temporary stabilisation measure was implemented to prevent any lateral expansion. Having worked with Propump Engineering on previous projects, Peter Brett Associates appointed the foamed concrete specialist once again to implement a foamed concrete solution.

Propump supplied 6m3 of foamed concrete to be pumped into the hole over a two day period. A strict envelope for the mix was specified, which Propump met in all aspects with a foamed concrete application of 1100 kg/m3 density. The work was further complicated when the initial 3m3 of concrete disappeared underground leaving the hole to be plugged a second time.

“Foamed concrete is an ideal solution for filling open voids particularly when access is good,” added Stuart Chandler. “Propump were mobilised quickly and were able to plug the hole prior to the implementation of a longer term solution.”

Foamed concrete is regularly used to fill underground voids, encapsulate pipes and raise floor levels, and its ease of application makes it ideal for building and construction sites when space is at a premium.

Pumpable and self-compacting, foamed concrete can mould itself to the shape of any void which makes it ideal for quickly filling these alarming underground voids. With the hole now stabilised and the client’s home not at any further risk, Propump has played a crucial role in this project.