Systematic Uplift Protection: The Raith Interchange
Currently, Transport Scotland is widening the country’s motorway network. As part of this initiative, the Raith Interchange, an intersection on the M74 Motorway that is used by 75,000 vehicles per day, has been expanded and opened to traffic in February this year. In this area, a new, 560m long and 35m wide underpass has been built underneath the existing M74.
At the Raith Interchange underpass, several bored pile retaining walls had to be built on both sides and tied back using DYWIDAG Strand Anchors. Furthermore, the base slab was secured against uplift by tension piles.
Albion Drilling, the specialist Geotechnical Contractor, installed 480 permanent, double corrosion protected 4 strand DYWIDAG Strand Anchors as well as 130 temporary, 5 strand DYWIDAG Strand Anchors in lengths of 20-25m each. The anchors were used tosupport the contiguous bored pile retaining walls forming the underpass and have loadbearing capacities ranging from 1,200 to 1,800kN. The temporary anchors stabilized the excavation during the construction of the base slab.
DYWIDAG Strand anchors are used when either the anchor load exceeds the capacity offered by solid bar anchors or if access to the drilling area prevents the efficient use of long lengths of bar anchors.Strand anchors are supplied to the jobsite prefabricated and coiled and can then be unwound and installed in the borehole using an uncoiler. DYWIDAG-Systems International UK supplied the equipment needed for this purpose.
Due to the prevailing geology and the depth of the excavation, double corrosion protected GEWI® and GEWI®Plus Tension Piles were used to resist uplift of the base slab in addition to the strand anchors.
Albion Drilling installed 300 GEWI® and GEWI®Plus Tension Piles using the equipment supplied by DSI. Unlike the DYWIDAG Strand Anchors, these tension piles were not prestressed, but will begin to resist uplift of the slab from artesian pressures if such loads are encountered. The GEWI® and GEWI®Plus Tension Piles can accommodate the dynamic loads caused by traffic on the roadway slab. Although double corrosion protection is not required in order to achieve a permanenttension pile, consideration was given to the expense that replacing the piles would cause, and therefore, the maximum corrosion protection option was chosen.
On other areas of the major project south of Glasgow, DSI UK supplied R32 DYWI® Drill Hollow Bar Soil Nails including couplers and plates for slope stabilization work on both sides of the roadway.