With increasing traffic on the N3 threatening to create unacceptable levels of congestions and unsafe travelling conditions on the pass, the decision was taken to investigate the possibility of a new alternative route to both the existing N3 and prior planned unsuitable alternatives for the N3 across the mountainous escarpment.
Initial Design Stages
The N3 Toll Concession Company, which is contracted to the South African National Roads Authority, examined a number of route options and a full feasibility study of route options for the Van Reenen Pass was completed in 2009. The Australian ‘Quantm’ route location software was utilised to map the position of the proposed routes, containing detailed information of the geometric parameters and constraints, cost of earthworks, layer-works and surfacing, and bridge and tunnel construction costs. From all the relevant data inputs, the Quantm software produced a variety of route alignment options for comparison. A 3D “string” was used to define a 500 metre wide corridor to be mapped from high accuracy aerial photography taken specifically for the project. This was then entered into the geometric design software, a South African legacy 3D roads design application (CARDS) where it was superimposed on the aerial survey mapping. Final adjustments were then made to the design following site surveys and ground core samples analysis.
Transfer to Civil BIM
The project was then transferred onto a Civil BIM platform, Civil 3D to facilitate the design to visualisation process. This involved a number of technical challenges, requiring careful planning at the outset. The processed aerial survey model which contained over 5 million points was further optimised by limiting full detail to the design corridor and degrading the point density outwards. The planned route was broken up into four sections, each referencing a common geometric alignment, to optimise performance whilst maintaining a dynamic design relationship.
The advanced capabilities of Civil 3D enabled complex design criteria to be addressed, such as benched (terraced) slopes for deep cuttings and high-fill embankments. Road-works and drainage quantities were extracted from the BIM software and a bill of quantities was compiled for costing purposes. The use of BIM helped streamline the design to drawing process through the use of tools for the automation of drawing production and custom visual styles for the representation of model data to South African standards. The creation of a 3D visualisation of this large transportation scheme proved invaluable as an aid to visual assessment by the design team, and in effectively conveying design intent to the client, roads authority as well as to the public in the consultation process.