Early theories why Wiltshire

Early theories why Wiltshire road buckled and cracked
24 FEB, 2022 BY CATHERINE KENNEDY
3/4 The council is awaiting a report from geotechnical specialists
4/4 Remedial works have been undertaken on the road in the past
1/4 Large cracks have appeared in the B4069 road near Lyneham in Wiltshire
2/4 The road has been closed since 17 February
3/4 The council is awaiting a report from geotechnical specialists
4/4 Remedial works have been undertaken on the road in the past
1/4 Large cracks have appeared in the B4069 road near Lyneham in Wiltshire
2/4 The road has been closed since 17 February
3/4 The council is awaiting a report from geotechnical specialists
4/4 Remedial works have been undertaken on the road in the past
Ground movement triggered by increased pore water pressure build-up is likely to have caused large cracks that have appeared in a Wiltshire road, according to a leading geotechnical specialist.
The B4069 road near Lyneham in Wiltshire has been closed since 17 February due to subsidence.
Geotechnical specialist Clive Edmonds told NCE that images of the damage - which show the road surface "heaved and then falling away in level" - suggest that "mass movement of the slope has been triggered probably by locally increased pore water pressure build-up in the slope profile leading to renewed landslide activity".
He added: "This sort of movement would account for the highly irregular switch-back look along the road alignment and cracking of the surface.”
Edmonds explained that the road “coincides geologically with an area where the Jurassic age Stanford Formation (limestone) appears to overlie/overstep the Hazelbury Bryan Formation (sandstone)”. Both of these are underlain by the Oxford Clay Formation.
"The road appears to run along and down the contact between the sandstone and limestone above the clay stratum going downhill away from Lyneham," he said.
“This kind of geological contact tends to be prone to past periglacial weathering effects like cambering and mass movement so is likely to have been affected in the geological past by downslope mass movement of the sandstone/limestone strata over the clay."

According to Edmonds, it will take "time and money" to safely re-instate the road.
"Remedial works will need to investigate and locate the slip surface at depth and design measures [will be necessary] to drain the slope to alleviate pore pressures in order to stabilise the movement noted before any re-build of the highway can be undertaken," he said.
The council has also said the issue could take up to a year to fix and cost millions of pounds, with cabinet member for transport Mark McClelland telling BBC Radio Wiltshire that the damage is “not something that can be resolved in a matter of days or weeks”.
"It could costs hundreds of thousands or up into the millions [to fix],” he said. "There is significant damage to the road. It could be up to 12 months in total.”
Wiltshire Council is currently awaiting a report from Atkins – and McClelland said it would wait until it receives this before deciding the next steps.
"The underlying ground has slipped and we need to understand why that has happened," he said. "This road has been subject to remedial works in the past and it has been a difficult road to deal with, but we've never seen anything like this before."
McClelland added that the road had "buckled" by around a metre in places.