Dorset Council will increase its monitoring and work to direct the flow of rainwater on old Castle Road in Weymouth, following a specialist geotechnical report after a landslide earlier this year.
The report has identified the contributory factors associated with a landslide near Old Castle Road and has set out recommendations for the monitoring of the area, and possible action.
A drone-based topographical survey of the slipped area will be carried out to help monitor ground activity. If there is any sign of collapse observed in the road, it will have to be closed and alternative emergency access arrangements will be provided for residents.
In March this year, the highways structures team was notified of a landslip on private land coming to within a few metres of Old Castle Road. Inspections of the area found no sign of distress in the carriageway but as a precaution the road was reduced to a single lane to move drivers away from the immediate area of the landslip.
Temporary traffic lights were put in place to facilitate the single lane operation as driver sightlines are not very good with the narrowing of the road.
Dorset Council commissioned Jacobs to undertake a site inspection and cliff assessment of the area to better understand future cliff recession scenarios and the risk of damage to the highway. The council’s highways team also looked at the feasibility of establishing alternative access for properties and businesses near the landslide.
The geological report identified a Translational Landslide – a down-slope movement of material – caused by a natural process of rainwater drainage through the land; nearby inland rainfall soaks through more permeable layers of material until it finds clay, it then runs along the surface of this clay layer downhill towards the cliff.
Cllr Ray Bryan, Portfolio Holder for Highways, Travel and Environment, said: “The details in the reports are essential for us to start planning how to ensure continued access to properties and businesses along Old Castle Road.
“Although the current dry weather means there has been little change in the area of slipped land, as seen along other coastal areas in Dorset, this can change quickly with prolonged and heavy rainfall.
“We will be carrying out some minor highway works to prevent the flow of surface water over the slope and we’ll undertake fortnightly monitoring of the area.
“Due to the slip being on private land, which has planning permission, we are currently investigating the legalities of what can be done, and by who, as engineering work on this land could affect any future development.”
This summer, a continuous kerb line of 45m will be built between the garage adjacent to a residential property and the footpath down to the beach to prevent surface water from entering the landslide system.
Council engineers will carry out regular inspections for signs of cliff retreat, subsidence and tension cracks to identify ongoing movement and risk.