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The Nant Ffrancon wall stabilisation
project is part of maintenance work to the main A5 trunk road
in North Wales. The object of this Welsh Office project was
to reinforce an existing stone wall running along the west side
of the carriageway.
The project was specified in six phases, with
work being carried out over a period of three years. The height
of the wall increased with each phase, from 1.5m to 10m. |
Part of the reinforcement for
Phases 5 and 6 consisted of installing Weldgrip Epoxy Soil Nails
into the wall and under the road. The nails are of a tubular
construction, with an O.D. of 32mm and I.D. of 15mm.
They have a tensile strength of 470kN and a shear strength of
190kN.
The nails were installed into 76mm diameter holes and pumped
with O.P.C. Cementitious grout.
Pump pressures of up to 55 bar were recorded. |
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To improve the aesthetics of
the finished work, the nail end assemblies were countersunk
into the wall, by overcoreing the holes, 250mm long by 150mm
diameter.
The end assembly consisted of a 125mm plastic plate and a nut
capable of withstanding 90kN of end load. Nail lengths of 10m
and 12m were used. |
To validate the grout/rock interface a
series of sacrificial pullout test nails were axially loaded
to 140kN. Also 10 percent of the production nails were pull
tested to the designed working load of 40kN. |
The system advantages of using Epoxy tube were:
Ease of installation
The light construction enabled longer lengths of tube to be used
High corrosion resistance
Cost
effectiveness |
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Bar
& 'AT' Rockbolts
