At first glance you'd be forgiven for asking, has the building 'jumped-up'? has a row of bricks been removed? or has the paving and ground sunk away?
In this instance we are looking at the result of a "sinkhole". The ground is made up of various layers beneath the building; sands and gravels on top of Palaeogene age clay, silt and sand, which is then on top of Cretaceous age chalk. We're talking pretty old stuff! Although generally rare, some geological areas do suffer from dissolution of the chalk, causing 'faults' in the rock formation. One of these 'unfortunate' areas is Flackwell Heath (nr High Wycombe), the location of this 1970's Building.
Often these faults will go undetected, visually at the surface (and even at standard foundation excavation depths) the ground would have looked 'normal' when the house was built. The 'fault' has been there for a longtime, by "a longtime" we're talking in terms of 'geological timeframes'. So the builders were seeing just the top layers; it is what the situation was beneath that is the issue. In this instance increased water within the upper ground layer (from a burst water pipe) washed away ground materials (the clays, silts and sands) into the historic chalk 'cave' or 'hollow' beneath, so the foundations have lost their support and sunk too.
This photograph was taken shortly after the ground movement started... already a 3-4 inch (75-100mm) gap has formed in places. Amazingly the building has stayed standing, with brickwork left 'dangling'. It wasn't going to stay that way for long.
The ground beneath the building was pumped with grout to fill and stabilise it. The initial damage that occurred, within a matter of hours, for this building was structurally too extensive and therefore after assessment it was decided that demolition was the best course of action to take. Clearly a devastating situation for the owner, who had lived here for many years, unaware of what laid beneath.
One of the great difficulties is that dissolution of the chalk can be very 'patchy', localised and impact relatively small areas. Just because one property is above a 'fault', it doesn't mean that it's neighbour is too. We offer Defect investigation and Appraisals of movement within houses, giving reassurance as to the significance and seriousness of cracking.
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