10 February 2010
ENVIRONMENTAL SUCCESSES ACHIEVED ON TSITSIKAMMA ROAD CONTRACT
A solid commitment to minimising the impact on the environment underpinned all work done during the recent upgrade of the N2 between Tsitsikamma and Witelsbos. Concor Road & Earthworks recently completed its contract to upgrade and widen a 14 km section of this national route, under supervision of Aurecon/Asch Joint Venture and with SANRAL as the Employer. Significantly, some 4 km of the road falls within the Tsitsikamma Indigenous Forest in the Plaatbos Nature Reserve under the control of SANParks.
Situated on the beautiful Garden Route, the Tsitsikamma Indigenous Forest boasts sheer ravines and gorges with some of the oldest yellow wood trees in the country within its dense foliage.
The rationale behind the upgrade and widening of the road was primarily to ensure safe passage for vehicles as much of the old road had no emergency shoulders to accommodate breakdowns or accidents. In addition to this, the road also had an uneven horizontal profile which severely limited line of sight for motorists.
The scope of work on the project included the widening of the road to accommodate emergency lanes and flattening the horizontal planes to increase visibility. This involved the realignment of the road, the removal of undulations so as to create a better geometric shape and the upgrade of the sub-surface; of which has resulted in a significantly improved driving surface. To fall in line with the N2 standard the road has been widened from 6 metres to a 12 metre wide single carriageway with shoulders.
Jay Juganan, project manager at Concor Roads & Earthworks, explains that the region’s geological lithology is such that, with the high moisture content, there is extensive decomposition of the underlying rock and this necessitated the excavation of all unsuitable material including the entire old road as well as the excavation of cuttings to a far greater depth to ensure the integrity of the final product.
All waste material was removed and spoiled in the two quarries that Concor Roads & Earthworks established for the crushing of material for the road contract itself. It is significant that these spoils will form part of the quarry rehabilitation process. “A differentiating factor on the contract was that all materials of construction were produced on site, including the structural concrete, the crushed layer works and the asphalt,” Juganan says. “By doing this, we were able to ensure supply and quality, and this was an advantage with the site being some distance from commercial sources.”
Commenting on the actual road construction, Juganan says a rock fill pioneer layer was placed along the full length of the road, and the fills on top of this layer were built with a finer rock fill which was blasted and crushed at one of the two quarries established to service the contract. The pavement itself comprised two selected crushed layers, two cement stabilised sub-base layers and a G1 base layer with a 40 mm asphalt overlay. It was necessary to blast and crush all the materials of construction as there was no suitable material available in the region.
The old bridge which carried traffic over the Kruis River has been replaced by a four-span bridge which at 25 metres stands much higher than the previous one, and is much wider. This was done to facilitate the realignment of the road, and to ensure safe passage for vehicles. The concrete used on this bridge structure has a high durability which will protect the structures in what can only be described as an aggressive environment with its consistently high level of moisture.
While the desire to ensure optimal travelling conditions was a priority, this was outweighed by the need to preserve the environment and full time environmental officers have been intimately involved in the day to day construction operations to ensure adherence to the Environmental Management Plan and the ROD in this environmentally sensitive environment.
Construction activities in such a sensitive environment bring a host of challenges, not least of which is the need to educate and train all personnel, almost all of whom were not used to constructing in such a sensitive environment.
Working in a confined area added to the challenge bringing with it plenty of constraints from a logistical perspective including minimal flexibility with access routes and the need to use smaller plant and equipment.
Methodologies, systems and processes had to also be put in place to deal with potential material spillages including oil, diesels, cleaning materials and pesticides required to control alien vegetation on disturbed areas.
Much of the road was built in half widths because of the need to preserve the forest which was right next to the road’s shoulder. The first step, and a requirement for environmental purposes, was the erection of a fence as a visual and physical barrier between the construction activities and the environmentally sensitive forest.
John Allen, environmental control officer for Aurecon/Asch Joint Venture, says all construction activities in the forest were based on a method statements which were approved by the project’s Environmental Management Committee (EMC) which met once a month.
One of the first steps on the project was the clearing of the section of the forest where the road widening was to take place. The southern side of the road had been cleared in the 1950s and again in 1979. The bigger trees in this area were left to grow larger for harvesting some decades later. These were, in fact, harvested by SANParks and sold at the annual timber auction. This was “pioneer” forest as opposed to “climax forest. Those trees considered viable for transplantation were carefully removed, retaining most of the root ball and were put into a storage nursery established for this purpose.
“During this process it was accepted that some of those trees selected would die because of root disturbance, and that those which survived would have established a smaller root ball system and would certainly survive transplantation back into the forest area once the road was completed,” Allen says. In total 1400 trees were removed with girths varying from 50 mm to 200 mm from an area with a swath of 10 metres and a length of 3.5 km (35 000 m2).
Allen says that this was the first time that this type of transplantation had ever been done, and quite an amount of “out of the box” thinking had to be done when refining the methodology for transplanting these indigenous trees. “We looked at the specifics of the region and the species themselves, and developed what we felt was a best practice and integrated approach to this, and it has proved the correct route to have gone,” Allen says.
Of the remaining trees in this area, those suitable for commercial timber were felled for this purpose, while those remaining trees not considered viable for transplantation were felled and chipped. These chips were stockpiled, and these chips have been used as mulch on the sides of the completed road. The top soil from this area was also removed and stockpiled for future use. Allen says in total 6000 m3 of top soil was stored and reused on the project to rehabilitate verges.
Another major consideration on this road contract was the actual placement of the culverts. To facilitate rainwater drainage along the route, and to allow access to both sides of the national road, fifteen in-situ culverts and ninety-eight pipe culvert crossings were constructed. When the road was designed the culverts were placed where previous culverts had been, and most of these were not on the actual watercourse so would not be functional.
“The positions of the culverts were changed to accommodate the watercourse itself, and while this sounds like it was a fairly simple change to implement it meant that each culvert had its own specific design so that it conformed to the environmental conditions that existed where it was being constructed,” Allen says.
Juganan says that constructing culverts in the forest was a challenge. “Construction activities were not allowed to exceed a specific predetermined footprint which in this case was only one metre beyond the edge of construction or toe of construction. This required careful and extreme consideration during all excavation with the majority of it being done by hand as it was neither feasible nor advisable to use large machinery in this small area.
“This, of course, extended the duration of this particular construction activity as it was no longer a case of constructing a standard size and shape culvert,” Juganan adds.
All watercourses have been fitted with silt screens in line with the environment requirements.
Vertical retaining walls were used on certain sections of the road and this allowed the footprint of the road to be reduced which was considered important in the forest itself. The retaining walls in the forest section were filled with the top soil which was removed from the forest months before and then planted with a careful selection of indigenous plant material including Heliochrysum sp, which is known for its hardiness and easy cultivation. Allen says that it was important that the root system of the selected plant material would not compromise the structure of the retaining wall.
In some areas very steep fills were present and it was necessary to protect and stabilise the top soil on these slopes which was accomplished using battens. “Most significantly, in this application we used indigenous dead branches from the nursery as battens to reduce erosion on the steep fills and then planted Plectranthus fruticosus which, while it has a widespread distribution in the forest, was collected within the road reserve. These cuttings were rooted at the nursery prior to planting on the fill areas,” Allen says. Some 24 000 cuttings were generated to ensure sufficient plant material.
The old picnic site alongside the N2 had degraded quite badly over time, and it has now been rehabilitated with trees transplanted from the forest. “We have had a 60% take on these trees which sprouted in early spring of 2007, however, the heavy rains of November 2007 flooded the root systems, with many dying back. The root stock is now coppicing and in time will be come trees,” Allen says.
The parking area at the “Big Tree” viewing site in the forest was closed during construction because of constraints, and the opportunity was used to transplant trees to this area and these are already sprouting,” he continues.
Much was also done to mitigate against any man-made damage within the forest and Haleria lucida sp (tree fuscia) was planted in between the trees in the forest and along the edge of the forest. Allen explains that these plants fulfill the role of a pioneer species. “When you cut the forest in a clean break, such as the construction activities did, you open up the forest and allow drying winds to blow through which affects the top soil and the vegetation. Planting a pioneer species mitigates against this by reducing air flow at the edge of the forest.”
The most publicised environmental intervention on this contract was the steps taken to protect a 500 year old Yellowwood tree. “The major concern with this beautiful specimen was that during road construction the roots or even the tree itself could become damaged,” Allen explains.
To ensure this would not happen, a 40 metre span, 2 metre high bridge was constructed using precast beams, and vehicles now drive right next to this massive tree but the bridge structure has provided appropriate and certain protection for the tree and its roots.
“During the construction activities it became apparent that the tree had sustained some old accident damage many years previously, and there was a piece of exposed wood which had rotted,” Allen says. “After some debate and consultation with experts it was decided to treat the tree by scraping out the wet rotten wood. This action was chosen as it will allow the living wood underneath to dry out and the tree will be able to heal itself.
Along other sections of the N2, the road is bordered by farmlands, settlements and plantations and the environmental considerations in these areas required different solutions. Majority of this area is covered by fynbos.
In order to rehabilitate the fills, cuttings and fynbos seeds were harvested by vacuuming along the N2 road reserve between the Salt River and the Kareedouw turnoff. Allen says harvesting was carried out every two months in order to catch the seasonal changes between the many species of fynbos on the reserve. “This was done over an 18 month period and the seeds were suitably stored and sown towards the end of the project. This plant material was used to stabilise the slopes and provide vegetative cover,” he says. “To minimise the influx of alien plants, these areas will be weeded for a year after end of contract.
The bypass which was created to accommodate traffic flow prior to the commencement of the work on the N2 has now been seeded as well as the verges. Indigenous plant material was used to stabilise the shoulders. This bypass was in use for more than 20 months as a detour, and will now become a local provincial access road.
An environmental task still underway is the rehabilitation of the two quarries. “In these instances, the contractor will drill and blast which will allow the faces to collapse inwards and then we will place the top soil over these slopes,” Allen says.
Other CSI (Corporate Social Investment) issues which were addressed on this project include the training of local community members who were chosen by PLC (Public Liaison Committee). Training was given in basic road building skills, tendering and entrepreneurial skills. These individuals formed companies which then tendered for roadwork contracts within the village, and three tenders were accepted.
Juganan says that even though demobilisation has begun on the current N2 contract, Concor Roads & Earthworks has secured the contract to resurface a 40 km section of the N2 from Storms River to the Crags. This scope of work will include pothole and crack repair and the overlay of 40 mm asphalt. Work started on this contract in October 2009 and is scheduled for completion June 2010.