4th October 2019
Weather in the UK has been unsettled recently, and the cold, wet start to October has been no exception; Evy Hughes, Geologist at Terrafirma explores the latest sinkhole that appeared in Kent.
The residents of Allard Close, Orpington were concerned to find a large SGN lorry collapsed into a sinkhole on Thursday 3rd October, following a report to the local authority of a large pothole which developed approximately 2 months prior. Roads within the sinkholes’ vicinity remain closed. Residents are having to work around the commotion using alternative methods of transportation, with hope of prompt remediation.
The sinkhole has formed following the recent heavy rain fall in the south of England, as a result of ‘hurricane’ Lorenzo, which is expected to move south-eastwards later this afternoon and showering Kent with further strong winds and rain.
The area of Derry Down, in the London Borough of Bromley, is underlain by a mixture of sandstone and chalk bedrock. The sinkhole may have opened as a result of chalk dissolution, subsequently forming a natural dissolution cavity beneath the surface. Another possible cause may have been due to anthropological chalk mining: from our data, we have identified 5 possible ‘Deneholes’ (mining cavities within chalk bedrock) within 500 metres of the collapse. These mining features are often unrecorded owing to their historical nature.
Although we cannot be certain of the cause without an on-site investigation, substantial rainfall in recent days has likely intensified the rate of erosion and chalk dissolution leading to this collapse that appears to have triggered by the heavy overlying load of the lorry.
Similarly, this previous summer two sinkholes formed as a result of a period of heavy rain in the south-east of England, which caused the closure of the M25. Our blog can be found here: Sinkhole Causes M25 Closure
The Terrafirma Ground Report includes an assessment of both man-made and natural ground stability hazards such as chalk mining and chalk dissolution. For more information contact our team today.