Propump Engineering has stabilised the grounds on the site of a major chalk mine collapse in Reading. The firm, which specialises in foamed concrete, pumped some 250 cubic metres of the material into a chalk mine gallery on the south side of Castle Hill, an area in the affected Coley district.
Disaster first struck in the region during January 2000, when a 15ft deep crater opened up in the Field Road neighbourhood, swallowing two houses. Later that same year, a hole 26ft deep consumed a garden further along the road. Homes were evacuated and families rehoused for almost two years while work to fill in the underground chalk workings was carried out. Now, some eight years on, land beneath the surrounding properties continues to be inspected, and the necessary stabilisation works carried out.
Renowned for providing innovative and cost effective solutions to ground engineering and foundation problems, the project main contractor had dealt with Propump Engineering in the past. In need of a quick, mass bulk fill solution to secure the discovered chalk mine gallery at the rear of the block of flats on Castle Hill, it called on Propump first and foremost.
With a track record in providing quality service and accurate volumes of foamed concrete, Propump Engineering was trusted to get the job done.
“We specified Propump on this project because foamed concrete is a clean alternative to site batched bulk infill grouts,” explained the contractors Geotechnical Engineer Andrew Airey. “Propumps foaming process doubles the volume of concrete so the number of wagon deliveries was reduced by 50% which minimised disruption for the residents.”
Lightweight and self compacting, the foamed concrete was manufactured on site via a Propump In-line Foamed Concrete System (IFCS), through small bore access holes, to quickly stabilise the ground. Super efficient, the system allows full base material (sand, cement, water) deliveries and processes them on a continual basis into the specified foamed concrete. Not only does this reduce truck movements, but it reduces the time on site. In all, the solution took just two days to complete, after which it was ready to be reinstated into an outdoor garden area for the flats.
Designed and built exclusively by Propump, the IFCS pumps base material through a specially designed squeeze pump to an injection chamber housed on the rig. From here, the preformed foam is injected into the base material and forced through a series of in-line mixers. The two are then blended together to produce the foamed concrete which for this project was specified as being an 1100kg/m3 plastic density, with a target 28 day strength of 2n/mm2.
An extremely efficient method of making foamed concrete, the system provides a significantly more economic and environmental approach in comparison to other methods of foamed concrete production as well as being much safer than traditional concrete pumps due to lower operational pressures.