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Little Orme

Colwyn Road B5115, LL30 3AL, Wales, United Kingdom
2019
Customer
North Wales Wildlife Trust
Engineering
Daear Geo Consulting
Contractor
Colin Jones (Rock Engineering) LTD
Protected object
Road, Building, Touristic infrastructure
Corrosion protection
GEOBRUGG SUPERCOATING®
Stabilized area
100 m²
Exposition
South
Initial situation

Following the routine inspection of the rock face by Colin Jones Rock Engineering LTD it was noted that a few blocks needed further inspection to ensure the safety of road and footpath users on the B5115 Colwyn Road. Daear Geo Consulting (DGC) was asked to undertake IRATA inspections of the blocks. In June 2018 DGC completed the field inspection and reported that the blocks pose a rockfall risk.

The consequences of the blocks failing are likely to be severe, with the blocks traveling at high velocity to the base of the slope with a very high likelihood of crashing through the masonry wall and onto the road or the hotel premises beyond.

The rockfall, therefore, posed a risk to users of the footpath that traverses the slope.

Geology

The Little Orme is comprised of limestone with sub-horizontal bedding planes.
The jointing is orthogonal, defining large blocks. Generally, these joints are tight within the rock mass, however, due to weathering and block movement, they are often dilated on the rock face.

The limestone is made up of individual beds of varying composition, with a resulting variation in strength and resistance to weathering. As such the exposed faces display evidence of differential weathering rates. Horizons which are more prone to weathering will undermine overlying beds.

Over time the limestone blocks above will become unstable and will begin to topple forward, resulting in natural joints opening further. Eventually, the blocks will be displaced, and the process will start again.

Description

From the Daear Geo Consulting's assessment, three options were possible, removal of the blocks, stabilisation of the blocks or protection of infrastructure. Between DGC and Geobrugg it was agreed that the best solution would be to stabilise the blocks. Geobruggs SPIDER® ONLINE-TOOL was used to model the blocks and to confirm the requirements of bolt spacing and bolt length along with confirmation of the mesh type.

Geotechnical specialists Colin Jones (Rock Engineering) LTD decided upon a safe system of work, methodology, and equipment to undertake the site works. Using 25 mm bar into a 42 mm diameter drilled hole secured with resin capsules. The anchor bar depth was between 2.5 and 3 m into competent limestone. Drilling of all seven bolts was undertaken with handheld drill rig.

Your local contact

Kevin H. Coyle
Kevin H. Coyle
Regional Manager Northeast
Natural Hazards
Geobrugg North America, LLC
3 Beaudet Terr
Columbia CT 06237 / USA
Phone +1 860 377 3230

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Saleh Feidi
Saleh Feidi
Regional Manager California
Natural Hazards
Geobrugg North America, LLC
8921 Emperor Ave.
San Gabriel, California 91775 / USA
Phone +1 909 706 8964

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John Kalejta
John Kalejta
Regional Manager Central US
Natural Hazards
Geobrugg North America, LLC
3215 67th Avenue Pl
Greeley CO 80634 / USA
Phone +1 505 220 1404

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Bob Lyne
Bob Lyne
Regional Manager Southeast
Natural Hazards
Geobrugg North America, LLC
8004 Windspray Drive
Summerfield NC 27358 / USA
Phone +1 336 337 0945

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Pierce Runnels, Civil Engineer
Pierce Runnels, Civil Engineer
General Manager Geobrugg North America
Natural Hazards
Geobrugg North America, LLC
22 Centro Algodones
Phone +1 505 771 4080
Mobile +1 505 400 0796

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Tim Shevlin
Tim Shevlin
Sales Director
Natural Hazards
Geobrugg North America, LLC
4676 Commercial St. SE, PMB 174
Salem OR 97302 / USA
Phone +1 503 423 7258

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