An investigation into a ground collapse that has closed the A26 in Kent has been launched by Kent County Council (KCC).
The incident earlier this week on Tonbridge Road in Maidstone has led to 10 homes being evacuated and the council has warned that repairs could take some time.
Drivers using the route first noted a depression in the road that then collapsed to form a hole a few metres across.
KCC’s highways division has said that its preliminary investigation has shown that a large void has opened up under the road and ground movement is continuing. Initial estimates suggest that the void could be up to 20m across.
“Social media posts have suggested that Clancy Docwra recently carried out road repairs at the site, presumably in connection with a water main, so the trigger for the collapse could be more complicated than heavy rainfall if there has been a recent water leak as well,” said sinkhole specialist Clive Edmonds, who is a partner at Peter Brett Associates.
“At the collapse location the published geology comprises Hythe Formation overlying Atherfield Clay Formation and the land surface dips gently southwards towards the River Medway. This area is prone to past periglacial weathering effects causing cambering of the Hythe Formation as it moves across the surface of the underlying clay towards the river valley floor. The sandstone/limestone strata in the Hythe Formation open up along joint planes to form a fissure with the overlying soil forming a “bridge” across the top of the fissure. However, if the soil bridge becomes inundated with water then the soil bridge can be eroded and weakened resulting in collapse at the surface.
“Fissures may only be a metre or less across but can be deep – up to 20m – so can easily provide a conduit into which the surface is swallowed up to produce a sinkhole that can measure several metres across at the surface.”
The site of the current ground collapse is less than 1km from a similar ground collapse in a residential street that occurred in early April.
KCC is also dealing with other smaller ground collapses on Bayham Road near Tunbridge Wells and at Goudhurst Road in Horsmonden.