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Hannah
Firth
Archaeological Projects Manager
Historic Environment Service
Somerset County Council
County Hall
Taunton
Somerset
TA1 4DY
UK
Tel: 0300 300 6603
Fax: 320229
The Chewton Mendip Turnpike Wall Restoration Project was undertaken to improve the condition and safety of walls on the section of the A39 between Chewton Mendip and Bathway. The project was a Somerset County Council (SCC) initiaitive with backing from the Countryside Agency, Mendip Hills AONB, Somerset Highways, Waldegrave Estates and English Heritage via the Aggregates Levy Sustainability Fund (ALSF).
Throughout its length the wall had lost the majority of its pointing and was in need of substantial maintenance in order to preserve its integrity. Particularly in the centre section, the profile of the wall had slumped at various locations due to lack of support at its base as a result of the degredation of the conglomerate rock on which it was founded. The spray and detritus thrown up by passing vehicles had accelerated the degredation of the rock.
The A39 was a route formerly used by heavy quarry vehicles as well as other traffic. Vibration caused as a result will have contributed to the loosening and slumping of the stones making up the wall.
A deep pointing exercise was carried out in order to stabilise and preserve the west wall; grout was pumped into the core of the wall and joints on the face. The process involved the use of lime-based mortars and volumes were carefully monitored to ensure that the structural behaviour of the wall was not altered.
Where the wall was beyond repair, it was rebuilt in a style closely matching the existing, using the recovered stone. A smal amount of new stone was interspersed with existing individual stones to create a more consistent design (avoiding a ‘patchy’ look).
In order to avoid a ‘new’ look and preserve the wall's older style, cleaning of existing stones was minimal and mortar mixes using different colour sands was prepared. A few trial panels were examined by English Heritage to enable selection of the most appropriate combination.