Ilfracombe, North Devon
Sea Wall Strengthening
During the refurbishment of a holiday park in Ilfracombe, the owners were concerned by the poor condition of a sea wall at their site boundary. The wall is located above the high tide but is sometimes vulnerable to storm waves. Frederick Sherrell Limited carried out a ground investigation to establish the thickness of the wall and the ground conditions behind the wall. The investigation included coring through the wall, hand dug trial pits and probing.
The results indicated that the wall was quite slender and additional lateral support would be needed. Several conceptual design options were considered including rebuilding the wall, but to avoid disturbing the newly refurbished holiday park and to satisfy local planning conditions the preferred option was to use king posts tied back with anchors grouted into the bedrock. The masonry wall was also repaired and repointed where necessary.
The design of the works required the collaboration of Frederick Sherrell Limited with a local structural engineer who specialised in heritage projects. The works were successfully carried out by local contractors during the winter of 2022/2023.
Gem Bridge, West Devon
Ground Investigation
An integral part of the Devon Coast to Coast National Cyle Route is the crossing of the River Walkham, near Tavistock. The cycle route follows the old railway but the original railway viaduct was demolished in the 1960’s, so the only option for cyclists was to negotiate the steep sides of the Walkham Valley. A new bridge was proposed and Frederick Sherrell Limited undertook an initial desk study and walkover inspection on behalf of the Local Authority.
This indicated that there were mine workings in the vicinity of the bridge site and potential difficult ground conditions associated with demolition debris (from the original railway viaduct) on the valley sides and alluvium in the valley floor. The desk study was used to plan the ground investigation which included trial pits, probe drilling, geophysics and an underground inspection of an old mine tunnel.
Variable thicknesses of alluvium and made ground meant that multi-piled foundation bases were the most appropriate foundation option. A sacrificial pile was tested to verify that the load carrying capacity was as expected. The bridge opened in 2012
South Devon
Quarry Inspection
Quarry companies are required to carry out regular safety inspections of the excavated quarry faces and tips and to commission a geotechnical assessment at least every two years. Frederick Sherrell Limited carry out these inspections for many quarries in the South West. The field work is carried out by trained engineering geologists and the reports include recommendations for actions where potential hazards are identified.
RNLI Lifeboat Station, St Davids, Pembrokeshire
Rockfall Control Measures
Frederick Sherrell Limited were asked to undertake a detailed geotechnical assessment of the cliff face next to the proposed new lifeboat station and to use that assessment to prepare a detailed specification, drawings and bill of quantities for the rockfall protection works. These works were to be completed prior to the construction of the lifeboat station.
The cliff works were carried out in 2014 by specialist cliff works contractors (BamRitchies Limited). The works included vegetation removal, scaling , netting and rock anchoring. Regular visits were made to the site by an engineering geologist to answer geotechnical queries and to make sure the works were carried out in accordance with the specification.
Dartmoor, Devon
Old Metalliferous Mine Site
Dartmoor has a long history of mining for tin and other metalliferous ores. The remains of some of these old mines are still clearly visible in the remote areas of open moorland but in other, more populated areas, very few signs of the mining legacy remain.
Sometimes, when appropriate safety precautions have been implemented, it is possible to gain entry to the underground mine workings. At a site on Dartmoor, Frederick Sherrell Limited carried out an underground survey of the old mine workings which was then used to assist in the assessment of stability of the old mine workings and the ground above. The survey confirmed the presence of a mine shaft that was subsequently uncovered at the ground surface and permanently capped.