COLLAPSE OF disused chalk workings is thought to be the cause of a 6m-diameter crater that has closed the A2 trunk road between Blackheath and Deptford in south east London.
The Blackheath Hill section of the carriageway, which is a major traffic artery into and out of London, was immediately closed in both directions after the collapse on 7 April. It will remain closed for the foreseeable future. Greenwich Borough Council temporarily evacuated 37 households as a precaution.
Chalk workings are suspected as the most likely cause. Chalk was excavated and burnt in kilns to produce lime for mortar and for use as a fertiliser. Early Victorian records describe a cavern in the locality 'cut out of chalk to a depth of 160 feet' (50m).
Engineers from Transport for London (TfL), which operates the road, and consultant Parkman - which maintains the road on TfL's behalf - were immediately on the scene following the collapse.
The hole was plugged with gravel, but further settlement of the carriageway meant investigations to determine the extent of the void could not begin for eight days.
Initial investigations using ground radar indicated other voids may exist beneath the carriageway.
As GE went to press further site investigation using cable percussion rigs was under way. TfL said it hoped to be able to give a likely date for reopening by early June.