The formation of a ‘sinkhole’ beneath a property in Wednesbury, West Midlands has received abundant coverage from the mainstream media during the last week. At Terrafirma, we have been looking into this event to try and understand more about its cause and wider context.
On September 25th, 2017, a large sinkhole appeared on the pavement at a pedestrian crossing in Brow Gate, Baildon, causing traffic disruption indefinitely. According to a pedestrian, the sinkhole opened within a time frame of a few minutes. Gas engineers from Northern Gas Networks are assessing the damage.
The local geological conditions are favourable for subsidence; superficial till (composed of clay) deposits shrink under prolonged dry conditions and 19th Century, unrecorded utilities infrastructure may be the cause of the collapse.
A sinkhole has been reported to have occurred within part of Beechwood Avenue, Cimla in South Wales. This is the second reported sinkhole in the neighbourhood after another ground collapse, later identified to be a mine shaft, opened up in January of 2016. The sinkhole is now being investigated to identify whether it is associated with the extensive shallow coal mining known to have occurred in the area during the 18th and 19th Centuries.
The age of solely relying on data in environmental risk assessment is over, with a visible shift in the way professionals perceive risks such as contaminated land and flood. Where historically data alone was enough to accept due diligence, now both a professional opinion and interpretative data modelling is a standard in assessing and managing these environmental hazards.
However, despite the significant annual financial expenditure (between 4 and 15% of all Buildings Insurance Claims in the past 5 years were attributed to subsidence) and the increasing visibility of the ‘Sinkhole’ phenomena, this shift in due diligence process has not been replicated in assessing the risks the ground pose.
On May 2017, an 8-metre-deep sinkhole appeared on High Street Green, Hemel Hempstead, causing the road to be closed until around November. This is in the same neighbourhood (within 200 metres, or less than a 10-minute walk) from the 6-metre-deep sinkhole that opened up in Oatridge gardens in 2014, resulting in the evacuation of 17 people from their homes .
On 29th June 2017, a 6 metre wide and 3 metre deep sinkhole opened in the middle of a busy Liverpool commuter route to the M62, Edge Lane, closing it for several weeks. United Utilities were called to the scene to assess the damage and discovered the sewer 6 metres down was blocked. The area rests upon superficial till rich with clays which are prone to subsidence which in turn can damage subsurface utilities.