New KZN freeway a true cliffhanger
Award-winning team does it on budget, on time, in style
SHATTERED rock challenged road construction along four kilometres of a steep road hugging a cliff on a section of a new route to link New Germany and Ntuzuma that will be known as the Dumisani Makhaye Freeway.
In a valley below, a forested river course had to stay unaffected. Then, after work had begun in 2013, a new requirement sprang up: for the MR577 to be able to accommodate eThekwini’s Bus Rapid Transit system (BRT).
But it was worth every moment of the stress for all involved in the MR577 project as they have won the technical excellence prize in the prestigious South African Institution of Civil Engineering regional awards.
From an environmental point of view, things would have previously been done differently.
“Forty years ago we would have encroached on the valley, but things aren’t done that way any more, and for good reason,” said consulting engineer Gary Swart.
Up above the road was a stretch of fissured sandstone with a habit of cracking away when disturbed, which meant that special “benches” had be cut into the hillside.
“We were worried that the rocks would come down on the workers,” added resident engineer Peter Jerome.
“We had to put in loads of safety precautions.”
Commenting on accommodating the BRT system, Swart said: “It was obvious that it would be difficult and expensive to retrofit a BRT component into the project when it was completed, and so the process of engagement began to stitch the two projects together.”
This meant introducing a schedule that is not everyday practice in road engineering: drawing up new plans that had to be ready, day after day, with 24-hour deadlines.
They cracked it, finishing the project on budget and on time.
“The KwaDabeka Valley was the most challenging portion of the MR577 project as the road had to climb at an average grade of 6.2%,” read a project statement.
“The geo-technical challenges faced by the design and construction teams tested their ingenuity to the limit as solutions had to be found to ensure the stability of the rock face.”
The statement explained that to accommodate the alignment of the carriageways, a rock slope cut at 63 degrees to the horizontal was selected to optimise the geometry of the road and to minimise risk.
“Due to the steep natural slopes located above the crests of the cuttings and the evident numerous surface boulders, the vegetation there was cleared to bar down all sizeable boulders and stabilise or fragment potentially unstable large boulders that could not be moved.
“Rockfall interception measures were installed on in situ ground at the crests of the main cuttings utilising gabion basket structures which were anchored back into the cut slope, incorporating guardrail structures in selected places to increase the height of the interceptor walls. A rockfall trap zone has been incorporated in the design at the base of the cut slope adjacent to and below the road level.
“Draping of steep rock and boulder outcrops with steel mesh was designed to control the downslope movement of boulders – particularly to protect construction personnel.”
During construction of the platform to install the interceptor walls, intermittent open tension cracks appeared.
“The tension cracks were aligned along a major joint set and extended vertically by 4m to 7m. More detailed investigations showed that the in situ sandstone rock below the colluvial cover contained large blocks of sandstone that had moved or rotated, opening up tension cracks within the rock slopes that vary in width between 200mm and 640mm.
“Rockbolts and anchors were specified to stabilise the interceptor gabion wall structure and the cut face below the base of the interceptor walls by between approximately 10m and 14m.”
The parties involved were the KZN Department of Transport, eThekwini Transport Authority / GoDurban; consulting engineers Royal Haskoning DHV; Henwood and Nxumalo and contractors Group Five’s joint venture with Simbithi Construction.
The department launched the idea of the road 20 years ago but finance only became available in 2003, and construction began. It is scheduled to open next month.
The Dumisani Makhaye Freeway, which Swart compares with the building of the Cape mountain passes 200 years ago, is more than just an engineering feat.
“The vision of the Department of Transport was also to give access to employment and economic opportunities in New Germany and Pinetown for the people of KwaMashu, Inanda and Ntuzuma who need to travel there via the N2,” said Swart. “It saves them 14km.” Dubbed the “outer, outer ring road”, it also shortens the trip from Pietermaritzburg to King Shaka International Airport by 12km.
Its uMngeni Viaduct bridge at a point known to Dusi canoeists as the Pump House will be a fifth crossing of the river.
“The construction process has also seen community engagement, with schoolchildren and teachers learning about the project.
“In consultation with the KZN Department of Transport and the project liaison committee – made up of representation from the local ward councillors, consultant and contractors – a training centre was established which provided construction related skills training.
“A total of 637 local community persons were employed and 10 local sub-contractors were appointed during the project.”
Swart hoped this community involvement would lead to youngsters becoming entrepreneurs and engineers.
In October, the engineers will make sure that the judges of the national competition travel the road’s sweeping curves, protected by walls plastered with shotcrete, when they head for the Sibaya venue for what Swart called “the Oscars of engineering”.
Others who received accolades at the regional competition were the eThekwini Roads Division (Highly Commended) for the MC 25-C9 Underpass and Naidu Consulting (Commended) for the Tongati River Bridge Widening on the Main Road P714; both in the Technical Excellence Category.
SMEC won in the Community-Based Category for their entry Sanitation to eThekwini Informal Settlements (Phase 3) and Naidu Consulting was highly commended for The Rehabilitation of Main Road P107.