Geobear was contracted to provide ground stabilisation and slab lifting to the floor of a Church in Manchester, UK.
St Anne’s Church in Haughton, Greater Manchester, is a Grade I Listed Building. The foundation stone was laid on the 1st September 1880 and the church was finally completed on the 29th July 1882. The floor of the church had recently begun to sink and a solution was needed to stabilise the subgrade without causing any damage to the listed building.
Following a successful tender process, Restoration Projects Ltd appointed Geobear to carry out stabilisation and ground improvement works as part of a wider scheme.
A site investigation revealed that It was probable that the floor level within the church at the West end was cast onto made ground that was used to raise the floor level. The loose nature of the fill material suggested that any vibration caused during construction works or heavy traffic, could cause the soil to compact. The conclusion was that vibrations from works at the nearby M67 had caused the floor slab to settle.
When working on listed buildings, the chosen solution has to be carefully selected to minimise structural risk to the building. In this case a break out and reconstruction was not feasible due to the age and use of the site. An excavation scheme would have to be highly sensitive and would take many weeks to complete.
Geoebar was selected to deliver the stabilisation and lifting works due to the non-disruptive methods. The solution involves the injections of resin beneath the floor slab using 16mm drilled holes and the process requires no excavation or major works other than removal of the parquet flooring.
Our solution was to inject our specially developed geopolymer through the existing slab at 1.0 m centres across the 76 sqm floor slab. We injected material at three vertical placements at each point, across a total of 66 points over the floor.
Prior to the Geobear works starting, the existing flooring was lifted and we completed dynamic cone penetrometer testing at four locations to record the ground strength; post works we conduct further tests to verify we have achieved an improvement in ground strength.
The first step in the works was to drill the points as per the design drawing and subsequently insert the injection tubes. We insert the injection tubes to a depth of 2 metres and complete three injections via each tube. Once the injections are completed we cut off the tubes and fill the hole with a grout. The main contractor could then replace the flooring and pews.
The Geobear work was completed in four days and the post test DCP illustrated a blow count improvement of many multiples (see chart 1) to verify the sub base was completely stabilised.