The improvements to the A75 required the construction of a 204 metre long structure to carry a slip road on a ramp up to the Glasgow Road at Gretna. A reinforced earth solution was chosen for a 169 metre length of the structure, with the remaining, generally lower, section being constructed as a reinforced concrete cantilever wall. The reinforced earth section was up to 7.4 metres high, and comprised hexagonal shaped facing units and one of three types of reinforcement; plain galvanised steel strip, a polyethylene geogrid, or a coated polyester strip. A well graded sandy gravel, taken from a local borrow pit, was used as fill to the wall. No insurmountable problems were met during construction, and the structure was completed to time and budget. During construction the settlement of the footing to the wall was less than 10mm, and the outward movement of the face of the wall ranged up to 30mm. In the two years following the end of construction, further movements have been negligible. The total cost of the ramp structure was about £0.4M. The range in the cost of comparable sections of wall supported by the different reinforcements was less than 5 per cent. The finish to the reinforced earth wall is good and any combination of the facing unit and reinforcements should provide suitable for use at other sites. (A)
Abstract