Excavation on the Gautrain project in South Africa is set to peak early next year as the 6.68m diameter TBM is being assembled and will soon join the drill and blast (DBM) tunnel drives that have been underway for months on the rail link.
A total of eight faces will be under excavation at peak – seven DBM and the TBM drive – which Bombela Civils JV’s project director, Charles-Etienne Perrier, told T&TI would be ‘quite a challenge’.
The total length of tunnel on the 77km project linking Johannesburg, towns and the airport is almost 16km from Park to Marlboro Portal, excluding stations. Just over 13km will be excavated by DBM, mostly as single-track bores. By last month, more than 1000m of DBM excavation had been completed.
For the single track (45m2) section, which covers about two-thirds of the tunnel, the Bouygues-led contractor’s planned advance rate is 120m-140m per month, depending on geology. For the double track (74m2) sections the rates steps up to 150m per month. Pulls of 1m-5.8m have been achieved depending on rock classification.
A total of 15 jumbos are being used on the project – 2 x 3-boom, 9 x 2-boom, and 4 x single-boom rigs, most of which are computerised.
The Herrenknecht EPBM (S-386) is to excavate just over 2820m on the project from Rosebank towards Park station. Cutterhead power and torque are 2450kW and 5,685kNm, respectively, and total thrust is 40,500kN.
Geology along the alignment consists mainly of weathered granite though there is some silt, clay and hard boulders. Groundwater is at a minimum depth of 25m, there are several faults and cover varies from 15m-80m due to topography.
The tunnel was designed by Atkins. Bouygues has supplied the precast concrete segmental ring design and moulds to a local subcontractor. The PPP rail project is being built by Bombela Concession Co.
