Over the weekend a spokesperson from Geoinvestigates Reading Office told Sky World News that the sinkholes which had opened up in Oatridge Gardens, Hemel Hempstead and last week at High Wycombe could be attributed to either natural cavities or fissures in the Chalk geology which underlies both areas or mine workings in the Chalk. The workings date from 1700s – 1900s and have been identified in Nash Mills and Highbarns areas in the south of the town. Chalk was mined for building stone and burnt to form lime to spread over clay soils to improve agricultural land. Typically the workings were small and reached by a vertical shaft in the Chalk which would be infilled at the end of the shafts life, the miners moving on to dig another shaft nearby.
Geoinvestigate explained that because of water erosion and softening of the ground natural fissures or openings in the Chalk or man made mine opening eventually became so large that the clay soil which covers and hides these holes can no longer provide a solid bridge over it. The result is that the ground can collapse either gradually or as at Oatridge Gardens catastrophically and without warning. Where the ground failure is progressive and slower it is sometimes possible to see the signs of problems such as building cracks, building subsidence and the formation of saucer shaped depressions in the surfaces of driveways, roads, lawns or agricultural land.
Sky News were told by Geoinvestigate that they had accounts of sinkholes appearing as early as the 12th Century in the Darlington area of Northern England associated with the gypsum geology in this area. Known as the Hells Kettles these large holes were said to have been created by a ferocious earthquake in 1179. Local myth has it that they are full of green, boiling, sulphurous water. People and animals are allegedly drowned or eaten alive by the Pikes and Eels that infest their waters. The Hell’s Kettles are said to contain the souls of sinners. Some report that these people (and animals in some cases) can be seen floating in the pools when they are clear.
So sinkholes have occurred in the historical past and will continue to appear in the future. It is Geoinvestigate’s impression from the number of enquiries we have had about sinkholes from the public, homeowners and developers that the frequency of sinkhole appearance has increased in recent years and may be attributed to the changing weather pattern and the increase in prolonged periods of very heavy rainfall and flooding. Sky News were told that many sinkholes are never seen because they occur in isolated areas on farmland or on moorland where they are filled-up by farmers as they appear so probably many more are occurring than we think.
This is not just a problem affecting us in the South of England. It’s also a problem in Northern England as well as Ireland where a recent news report confirmed that a sinkhole opened up in the village of Tramore, County Waterford on 6 January and they are appearing all over the country. This was as a result of the recent wet and stormy weather they have also been experiencing. Geoinvestigate believes it’s possible that a large number of new sinkholes will appear as the inundation and flooding in the Thames Basin and Thames Valley recedes and the water levels in the ground drop which could take several weeks or months.
Sky were told that Geoinvestigate agreed that the evacuation of 17 homes at Oatridge Gardens, Hemel Hempstead was appropriate not only because of the risk of further ground collapse but because of the risk of explosions from the gas services which were left precariously dangling in mid air over the hole. Geoinvestigate told Sky News that until Geotechnical Engineers and site investigation teams can ascertain the extent of the underground instability problems everyone has to proceed very cautiously. We would expect a very intensive drilling programme to be carried out on a grid pattern around the collapse supplemented by a Ground Penetration Radar Survey (GPR is essentially an X ray of the ground if you like) to determine how far the problems extend from this location and which of the adjacent homes may be affected.
Geoinvestigate told Sky News “our thoughts are with the residents of Oatridge Gardens. The investigations could go on for weeks and the residents may not be able to return to their homes and pick-up their lives for many months if the ground has to be extensively stabilised – therefore it is imperative that all the parties involved (house insurers, geotechnical engineers and the Local Authority) get their act together quickly formulate an investigation strategy to identify and rectify the problems as soon as possible.
Issues about responsibility and financial liability should be put a long way down the list. It’s our experience that what is important (after what must be a very upsetting event for the Oatridge residents) at this time and what counts is “people care”. Making sure residents are comfortably accommodated for the duration and they are reassured and kept in touch about what is happening is what counts. They will also appreciate being kept up to date about what the engineers and the authorities are doing and also the finding of their investigations”.
Geoinvestigate told Sky News that if you are a developer, home owner, house builder, consulting engineer or project manager and you are worried or require advice about sinkholes and how they might affect your property following the collapses in High Wycombe and Hemel Hempstead contact Geoinvestigate at our Site investigation office in Greater London or our Middlesbrough or Windermere Offices. Geoinvestigate would be pleased to provide free advice about sinkholes or our sinkhole site investigation services covering the Chalk belt including the towns of Harlow, Bishop Stortford, City of Hertford, Welwyn Garden, Hemel Hempstead, Welwyn Garden, Luton, High Wycombe, Maidenhead, Reading, Newbury, Oxford, Swindon, Basingstoke, Aldershot, Guildford, Reigate and Maidstone.
Winding- up the interview Sky World News were told that from what Geoinvestigate could see of the collapses it may not be possible to save the buildings in High Wycombe and Hemel Hempstead, which are over or very near to the initial collapses and there may be no other option in some cases than demolition. Geoinvestigate are expecting many other similar problems to occur in the next few months.
