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Chapter 9. Topographical Surveying and Construction Control of Motorways

Volume 1 Part 3
Brief résumé of Chapter 9:
Topographical Surveying and Construction Control of Motorways

R. M. Buchan FRICS
formerly Chief Surveyor, Sir Owen Williams and Partners

Following Mr Newby's essay describing the roles of the Ordnance Survey's mapping in the development of Britain's motorway system, this Chapter adds the contrasting insight of a surveyor who served Sir Owen Williams and Partners through a career of 39 years. He was thereby engaged with his teams in the detailed processes of surveying in order physically to mark on the land the routes of motorways successively assigned to contractors for construction, taking account of the local risks of subsidence and its consequences in mining areas active at the time or in the past. It pulls together much the way in which this professional discipline closed the gaps and details and provided the site control for work described in Chapters 8, 9 10, and 13. The accuracy of the surveyor's work made a crucial contribution to effective drainage runs and to the accuracy required during the application of the various lean mix underlays and the top finish, usually of a bitumen based asphalt, that comprised motorway pavements.

Initially, horizontal and vertical alignment design followed the practice of first locating straights and then fitting circular arcs between them as on the M1. Long circular arcs presented special problems for setting out. This was partly because it is difficult to measure horizontal distances accurately. To do so properly would be unacceptably time-consuming, so errors would accumulate whenever a long curve was being set out by traditional means. Problems with the accessibility of bench marks etc., and inter-visibility, were much more likely to occur while setting out long curves. Nevertheless surveyors needed to be confident enough of their work to replicate it precisely at a later date. So surveyors sought ways of carrying out independent checks, if only as a means of control and verification. However, as we shall see when at work on the ground, factors they might have to consider for aesthetic reasons were not always apparent unless they grasped the local mining history and the form of the highway engineer's remit too.