The A82 Pulpit Rock Improvements – A Complex Propped Cantilever Viaduct

The A82 is a primary route in Scotland that follows the shore line of Loch Lomond. Following a landslide in the late 1970’s near the Scheduled Monument, Pulpit Rock, traffic lights were implemented limiting vehicles to one-way operation. A widening scheme was required to provide a two-way carriageway over a length of approximately 400m. This included a new six span 168m viaduct curved in plan to follow the existing road alignment and running parallel to the loch shoreline. The deck consists of a continuous open trapezoidal steel-concrete composite box girder supported on large diameter intermediate monopile piers socketed into the rock beneath. The construction was phased to minimise road closures. Partial construction of the deck facilitated switching of traffic to the new structure, allowing the remainder of the structure to be completed. This case study paper summarises the design and construction challenges of the viaduct.