Formation of the GNR Excavation, Filling & Embankmen

Today we can view the layout of the countryside below us from a helicopter or an aeroplane, fitted with specialised cameras, to make a record of the problems we face in construction projects. The Surveyor-General of the 1820s and his staff of Assistant Surveyors could only view the mountains, steep slopes, rocky cliffs, gullies, hollows, valleys and creeks by getting up on the highest ground around, as Mitchell did, to study and sketch possible routes. The alternative was just to tramp their way through the undergrowth and trees, making appropriate notes and using dead reckoning methods for the definition of the route.

Even with their cleared and surveyed path, its irregularities had to be overcome. They had to decide on methods for cutting around any steep slope, blasting away underlying rock, to make a road with a gradient that could be used by the vehicles of the time. That might entail embankment on one side of the cutting or even a massive rock structure to prevent slippage. It could mean embankment on both sides of the road over a hollow. In crossing a gully, hollow or valley, a raised structure could be required with suitable embankment supporting the road surface. In a gully with a creek running through it, the decision could be a bridge structure at a height to allow for flood conditions. Cutting, filling, embanking, bridging were all to be considered and that was a slow process, always bearing in mind the essential requirement for good drainage methods to prevent road washaways. In spite of the regularity of droughts, there were those times when it must have seemed that the prehistory Deluge had started again. The Assistant Surveyors were faced with the need to make decisions on any of these types of structure, with difficult restraints confronting them. Reference has already been made to some of these structures that were required.

Assistant Surveyor Percy Simpson reported in January 1830 that part of a Gang had been occupied in filling an extensive Hollow near 7 Mile Post and building side walls therein.. Part of No.25 Road Party have been employed excavating an approach (from the side of the Mountain) to the Bridge on the Line of Road running parallel to the North Shore of the River [Hawkesbury], widening the Road in places where required leading to the Bridge and side cutting and quarrying beyond and northward of the same. Others of the Party have been employed digging a Foundation for a side wall and in blasting and removing some extensive overhanging Rocks wherefrom the requisite width of the Road must be taken. Month in, month out, similar structures were put in place making the Great North Road, often in severe conditions of temperature, weather and land with ridges, cliffs, valleys, hollows, water courses and tough sandstone rock everywhere.