Posted on Nov 18, 2008 in Construction Technology & Machines
A rock crushing plant in Linbro Park will enable the recycling of excavated material so that no quarries or borrow pits need to be dug to obtain adequate construction material for the construction of the Gautrain alignment. This measure limits environmental scarring while ensuring responsible management of excavated material, called spoil.
The spoil will be collected from tunnels, cut-and-cover and other blasting sites. At the tunneling section, several methods will be applied to remove spoil. At Marlboro Portal, for example, haul trucks drive in and out of the excavated tunnel to collect spoil for removal. At the Rosebank Station construction site, where the Tunnel Boring Machine will excavate the tunnel, spoil from freshly bored sections will be removed on a conveyer belt to the tunnel opening. At Emergency Shaft 5 in Dunkeld and Mushroom Farm Park in Sandton, for example, buckets filled with spoil are scooped out of the shafts and pulled towards the surface by gantry cranes. The spoil is then dumped on the back of haulage trucks for removal.
As there is not adequate space to store spoil at the construction sites, haulage trucks will transport the rock to the crushing plant which is being erected east of Linbro Park. Since the tunneling operation is a wet process, spoil emanating from the tunnel operations are wet. This minimizes dust in the construction environment.
To lessen the effects of dust and the spreading of mud on road surfaces, wheel washers are installed at construction sites. Haulage trucks will first visit the wheel washers before being allowed to enter public roads. In addition, mechanical broom technology is used to sweep the roads close to construction sites.
After collecting spoil from construction sites, it will be transported to the crushing plant in Linbro Park. Spoil has no agricultural value or application and is therefore most suited as filling material. Typically, spoil will be used to construct the embankments of the surface rail alignment. This is done to ensure a smooth and even gradient for rapid rail transport.
The quality of spoil will be classified and material fitting the correct quality criteria will be crushed to the desired sizes using suitable crushing equipment. Once the rock has been crushed, it is sorted according to size and stored in temporary spoil stockpiles until needed.
Where the rail alignment runs on the road surface, dedicated haul roads are built along the route in the rail reserve. Haul trucks will use these roads to transport spoil and the crushed material for use along the alignment. A dedicated, temporary haul bridge is also erected over Allandale Road. Similar measures will be taken in other construction areas to lessen the impact of construction vehicles on public roads.
After all the embankments for the surface rail alignment are completed, vegetation will be planted on the slopes to combat soil erosion. A mix of indigenous and commercially available grass species will be planted. The grass cover is designed to contain a ‘mother crop’ that germinates very quickly and ensures quick erosion protection and stabilisation of the embankments. The ‘mother crop’ is then slowly replaced by more sustainable perennial species that ensures long term stabilisation on all areas that requires protection. Natural colonisation forms part of this process and ensure a low maintenance and hardened vegetation cover that ultimately assist in the protection of the rail alignment.
Apart from using spoil in the construction of the rail slopes, the Gautrain construction team is seeking opportunities to use this material to improve current environmental scars like old quarries, borrow pits and existing erosion dongas. It is envisaged to use spoil material at these types of scars by filling and contributing to the required environmental rehabilitation. Rather than creating new problems we will be looking at opportunities to contribute in reducing existing environmental scars.
All these measures are in line with the requirements of the Environmental Management Plan that guides the construction of Gautrain. These factors contribute to making Gautrain one of the most significant environmentally sustainable rapid rail engineering projects in the world today.
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