Transport Scotland has monitoring requirements for particular areas of the network with earthworks present. In the South West unit, we have a total of 16 sites comprising: 9 sites that require 6-monthly monitoring, 1 site requiring 12-monthly monitoring, the remaining 3 are monitored in the event of rock fall occurring. 3 additional sites have been added to our monitoring programme this year.
Further information on each of these sites can be found below:
A76 Blackwood (GA5)
The site is located along the A76 Dumfries – Kilmarnock Trunk Road at approximate National Grid Reference E290321, N588210. The A76 is a single carriageway, trending at this location broadly northwest - southeast. The trunk road in this area is constructed within a cut section bordering the carriageway to the east and supported on an embankment to the west.
It sits on an embankment approximately 5m above the River Nith which runs along the southwest of the road. The embankment rises at gradient of 1(v):1.5(h) from the toe of the embankment slope which is immediately adjacent to the river. At the crest of the embankment a verge of approximately 0.5m width separates the pavement from a safety barrier. To this east is a cut extending into the adjacent hills to the east. This site is subject to a slope stability monitoring regime at intervals not exceeding six months.
The embankment supporting the carriageway is displaying signs of distress with small areas of slip and terraces forming along a length of the embankment. The verge has settled locally with the adjacent barrier showing signs of distortion over approximately 50m length, brought about by ground movement. Remedial patching of the carriageway is evident at this location. Cracks in the northbound lane, outwith the patching, running parallel to the verge are likely to be associated with the instability of the embankment. The face of the embankment is covered by dense vegetation, shrubbery and mixed woodland. The presence of inclined tree trunks suggests that a creep or minor historic landslide has occurred. Drainage can be seen in the verge as grips perpendicular to the carriageway.
A76 Enterkinfoot (GA3)
The study area is located adjacent to the northbound lane of the A76, within the council boundary of Dumfries & Galloway. It is bound by the A76 to the west and River Nith to the east. In terms of topography, the study area can be described as a steep sloping area falling from east to west. To the east of the study area the land is gently sloping up away from the carriageway. This site is subject to a slope stability monitoring regime at intervals not exceeding six months.
The embankment supporting the A76 shows signs of recent slips and terracing causing displacement of the verge and safety barrier. At the toe of the embankment the River Nith has eroded the embankment, over-steepening it in places. The embankment shows signs of distress over a length of approximately 200m with small areas of slip and terrace forming along the length of the embankment.
A topographic survey has been carried out at Enterkinfoot, and a ground investigation was completed in 2017. Five options are being considered, including realignment of the road.
A77 Cairnryan (GA14)
The site of A77 Cairnryan is located adjacent to the A77 carriageway, at approximate National Grid Reference E205492, N571756, 3 miles north of Cairnryan. The A77 is a single carriageway at this location, trending northwest-southeast and is constructed on side-long ground rising to Mid Moile to the east and falling to Loch Ryan to the west.
Two landslides occurred at this site in late 2014. The northern landslide, adjacent to the southbound lane, occurred first, causing soil debris to spill onto the carriageway. The southern landslide then occurred immediately south of the northern one, to an area supporting the carriageway on the northbound side. Temporary remedial works have since been completed in the area adjacent to the southbound lane.
We have removed vegetation from the area of assessment and our geotechnical engineers have assessed the slope to allow a design for the ground investigation to be developed. The ground investigation has been designed and a specialist contractor has been procured. The Ground investigation was completed in 2017, and repair construction work is under way, scheduled to complete in March 2018.
A77 Carlock Hill (GA7)
The site is located along the M77/A77 Glasgow – Stranraer Trunk Road, at approximate National Grid Reference E209007, N576460. At this location the A77 is a single carriageway, trending broadly northeast - southwest. The carriageway at Carlock Hill is constructed on sidelong ground with hill side slopes adjacent to the northbound lane and a steep embankment supporting the southbound lane sloping down towards the Water of App. A single row of gabion baskets support the edge of the southbound lane. This site is subject to a slope stability monitoring regime at intervals not exceeding six months.
A landslide occurred on the hillside adjacent to the northbound verge in November 2014. Heavy rainfall over the following weeks induced further slides resulting in large volumes of debris being deposited onto the carriageway in December 2014. Interim remedial works were completed in May 2015 stabilising the area of failure using rock fill however further works including placing of rock fill, removing of loose debris and further assessment of drainage was undertaken on August 2015 to provide a robust medium-term solution.
Further works were required to provide an erosion control system on the exposed open rock faces that remained and this was completed by November 2015. Road patching was carried out in October 2015 to repair the areas that have been temporarily patched during the landslip site works. A Geotechnical Investigation is programmed at this site for 2017/18, with a permanent design to be developed and constructed in 2019/20.
A77 Carlock Wall (GA8)
The site is located adjacent to the A77 trunk road network, at approximate National Grid Reference E209286, N577030. The A77 is a single carriageway, trending broadly north to south, constructed on sidelong ground falling steeply to Altikelly Burn located at the toe of the Altikelly Glen to the east and rising to the west to Carlock Hill.
The A77 Carlock Wall monitoring site consists of an embankment section adjacent to SB carriageway, which is considered overly steep at approx 1(v):1(h) descending 5 to 20m to the valley floor where Altikelly Burn is located. A series of retaining structures are present consisting gabions, concrete bagwork and dry stone masonry retaining structures which support the SB carriageway and verge. Emergency remedial works were mobilised February 2015 and entailed packing out voids within the retaining structures with sand cement matrix fill sand bags and also undertaking works to stabilise the retaining structures by means of a new gabion basket. Defective pipe drainage outlets were also targeted along with localised areas of defective gabions, mainly where corrosion has caused loss of section and fill.
This site is subject to a slope stability monitoring regime at intervals not exceeding six months. In addition, monitoring pins in the carriageway are surveyed every month to check for movement.
A ground investigation has been completed for this site and options have been assessed. The recommended preferred option is a soil-nailed slope with a reinforced earth structure at the crest. This is currently being designed and is programmed to be constructed in 2018/19.
A77 Carlock Wall Rock Face (GA15)
The site is located adjacent to the A77 trunk road network, at approximate National Grid Reference E209286, N577030. The A77 is a single carriageway, trending broadly north to south, constructed on sidelong ground falling steeply to Altikelly Burn located at the toe of the Altikelly Glen to the east and rising to the west to Carlock Hill. The rock slope face can be summarised as approximately 100m long, with height varying from 10 to 15m. adjacent to the northbound carriageway verge. It is covered in draped rock fall netting throughout the site extents, pinned at the crest of the rock slope face. This site is subject to a slope stability monitoring regime at intervals not exceeding six months.
The rock slope face is showing signs of deterioration. Rock fall debris has accumulated behind the rock netting at the rock face toe. Vegetation comprising mainly shrubs are prominent on the rock slope face. North of the site unfavourable bedding cleavage and fracture cleavage can be seen in exposed rock face adjacent to the turn off leading to Carlock House.
A77 Drumbo Kennels and Mark Church (GA10)
The site of Drumbo Kennel is a section of embankment supporting the A77 trunk road north of Cairnryan at approximate National Grid References E206336, N573566. The A77 at this location is a single carriageway with an embankment supporting the northbound carriageway and adjacent to the southbound carriageway there is a cut section stabilised by soil nails. No significant defects have been recorded in the cut section stabilised by soil nails therefore this has not been assessed as part of the geotechnical monitoring as this has not been recognised as defective nor pose any risk to the public. West of the site the Water of App meanders, in line with the carriageway, and outfalls southwest into Loch Ryan.
The embankment, set back from the verge of the northbound carriageway, can be described as steeper towards its crest, with the toe leading to a broadly flat ground where the banks of Water of App are present, approximately 50m away. Geotechnical monitoring recorded areas of overly steep sections, areas of terracing, saturation and exposed soils at surface caused by erosion, all within the upper limits of this embankment typically surrounding a section that is 3-4m high, considered particularly overly steep. Towards the northern extents of the study area there are sections of 1 to 1.5m high near vertical exposed faces comprising clay with suspended cobbles . The northbound carriageway verge is recorded as settled up to 400mm, thought caused by soil erosion. Water ponding at the toe the embankment was also recorded.
A77 Glengall (GA9)
The site of Glengall is located in a cut adjacent to the M77/A77 Glasgow – Stranraer Trunk Road, immediately southeast of Ayr at approximate National Grid References E235174, N618896. At this location, the A77 is a single carriageway. The cut can be broadly described as 7.5m to 15m high. Only the east side of the cut, adjacent to the southbound lane, has been recognised as at risk. At the crest of the cut east of the A77, arable farmland extends east on broadly flat ground. Extending from the crest of the cut west of the A77 is grassland bordered by a residential estate. The cut adjacent to the northbound lane shows no sign of instability. This site is subject to a slope stability monitoring regime at intervals not exceeding six months.
The cut adjacent to the southbound lane shows signs of instability including tension cracks, terracing at the crest of the cut and bulging at the toe. A boundary fence bordered by arable farmland is located at the top of the cut. The ground of this field, bordering the cut, was noted as partially saturated on all occasions during the geotechnical monitoring particularly towards the southern end of the site. An open drainage ditch runs along the top of the slope and a herringbone drainage system is present throughout the cut. A single tier of gabion baskets extend along the toe of the cut, adjacent to the southbound lane. The majority of these have tilted to some degree, but some have settled extensively in one localised area.
A77 Bennane (GA6)
The site of Bennane is a section of natural hillside adjacent to the M77/A77 Glasgow – Stranraer Trunk Road, 6km north of Ballantrae at approximate National Grid References E211067, N588374. The A77 trunk road at this location is a single carriageway on a large-radius bend, with a climbing lane in the southbound direction. The northbound lane of the carriageway is supported by an embankment covered in various vegetation and mature trees and extends downslope to a levelled area in use by the caravan holiday park. The southbound lanes are adjacent to a steep hillside slope of approximately 30m in height. The slope plateaus at the crest and consists of rough grazing land. The verge adjacent to the southbound lanes is approximately 3m wide and bordered by a slip protection barrier. A safety barrier in the verge is also present throughout this section. This site is subject to a slope stability monitoring regime at intervals not exceeding six months.
The Bennane site is located adjacent to the southbound lanes and shows several signs of instability. Surface erosion and terracing is extensive in the upper areas of the slope. Approximately halfway up the slope a natural levelled terrace has formed, approximately 3 to 5m wide. A landslide occurred in late 2014, causing a significant body of soil debris to accumulate behind the slip protection barrier. The stability of the lower and upper slopes were monitored to determine whether any further signs of instability were present. A large number of cobbles and boulders are exposed in the slope face with further signs of erosion and washout. The crest of the lower slope is near-vertical in areas with exposed soil and terracing throughout. The slope adjacent to the verge is set back 5 to 6m from carriageway.
M80 Earnock Cut (GA1)
The site is located adjacent to the northbound carriageway of the M80 Glasgow – Stirling Trunk Road, at approximate National Grid Reference E262701, N667429. The M80 is a motorway, trending at this location broadly northeast - southwest. The site location is at a point where the M80 sits in a cut slope, running between a railway line and a residential development. The monitored slope is located adjacent to the northbound motorway lanes. The slope rises approximately 10m above the adjacent motorway lanes. This site is subject to a slope stability monitoring regime at intervals not exceeding six months.
Deterioration and instability of this slope is shown over a length of approximately 250m. The slope shows signs of distress with tension cracks developing and terrace forming in the top half of the slope. Bulging is evident throughout the slope mainly along the toe. Erosion channels can be seen throughout the slope suggesting historic drainage issues, confirmed by presence of herringbone drains along the length of the cut. Monitoring equipment is installed in two areas of the cut. The cut slope is covered partially by trees and vegetation which continues along the northern boundary of the site. It can be assumed that the existing vegetation contributes to the stability of the slope.
Our operating company, Scotland Transerv, conducts monitoring of these areas on our behalf in accordance with the methodology outlined in the Design Manual for Roads and Bridges. Sites recognised as having low or negligible risk have not been considered further but will continue to be monitored in accordance with the requirements outlined above. These sites comprise:
- A725 Whirlies Roundabout (GA13)
- A77 Holmston (GA11)
- A77 Kennedy’s Pass (GA12)
- A78 Chriswell (GA4)
- M8 Bishopton (GA2)