A1 TOWER AND DUNGLASS BRIDGE LAUNCHES

The A1 in Berwickshire was realigned to bypass the village of Cockburn spath and to remove loading from two 60-year-old reinforced concrete b ridges. This realignment required the construction of three major new structures. The smallest was a reinforced concrete bridge over British Rail's East Coast Main Line and the others were two-span composite st eel plate girder bridges supported on finger piers approximately 20 m above small burns in deep gorges. Each bridge has a ruling gradient of approximately 25% downhill from the south abutment. An innovative sys tem was adopted to launch the bridges down a slope which varied at dif ferent stages up to a maximum of 9%. The small plan area available on top of the piers meant that the jacks required during the operation ha d to fit within the Storey heavy rockers used for the launch. The nort h girder section was omitted from the launch and subsequently welded i n situ. The paper explains why this approach was adopted and describes the problems encountered and overcome on site.