Posted on May 13, 2009 in Construction Technology & Machines
Being one of a small group of specialists who pilot Tunnel Boring Machines (TBM’s), Sakkie van Zyl is usually at work in a foreign country. But when Gautrain imported its own machine to start boring a tunnel in Rosebank, Sakkie immediately packed his bags and returned home.
Born in the Free State, Sakkie previously piloted TBM’s in Singapore and Hong Kong for light rail and utility tunnels. In the United States of America, he worked for a company that assembles and tests TBMs’ before shipping machines to projects around the globe.
GAUTRAIN TBM PILOT, SAKKIE VAN ZYL
Sakkie’s passion for these massive rock eaters was triggered for the first time when he worked as an electrician on a TBM for the Lesotho Highlands Project in the early 90’s. For the project, six hard rock TBM’s were used to excavate three tunnels. Ironically, most of Sakkie’s Gautrain TBM team members are South Africans who worked together in Lesotho. “Because of the experience gained in Lesotho, South Africans’ skills compare to the best in the world,” says Sakkie.
“I am part of a very small TBM community. Although we work on different projects around the world, we always stay in contact,” says Sakkie. He explains that a team of 15 people would work underground on a shift that would last about ten hours. Also considering the confided space in which they have to work, it is understandable that people form life long bonds. Gautrain’s 885 tonne TBM measured 160m in length. It bored a single rail tunnel with a 6.8m diameter – it was one of the bigger TBM’s in use.
As a TBM pilot, Sakkie operates the latest international technology to steer the borer and to make sure it stays on its predetermined course. He relies on several computer screens to determine to way ahead. Screens also monitor excavation progress at the cutterhead where the teeth bore into the rock. Simultaneously, excavated material is removed out of the tunnel via a conveyor belt while complex machinery installs precast segments inside the bored tunnel to form a watertight and smooth lining. Being the pilot of this intricate moving factory is certainly not for the feint hearted.
“Our biggest challenge on Gautrain was the changing geological conditions,” says Sakkie. The TBM encountered variable granites – in places completely weathered and unstable, and in others extremely hard rock (up to 230 MPa which is ten times stronger than concrete) – all below the water table.
“It was very difficult to keep making adjustments and to know what is going on at the cutterhead,” says Sakkie. Remembering the subsidence in Oxford Road in July 2008, he adds: “When I arrived for my shift, it had already happened. Everyone was extremely tense.”
To deal with the complex geological conditions that the TBM had to encounter, Gautrain used a mixed face Earth Pressure Balance Shield TBM. It was custom built over a 12-month period in Germany and shipped to South Africa in the last quarter of 2007. Having completed its journey at the end of January 2008, the TBM was dismantled a few weeks ago.
“Until the end of September I will be involved in laying the concrete floors inside the completed TBM tunnel as well as cable ducting. But I have no idea what I will do after Gautrain. I am just happy to be home again. I missed the people and the food. It is wonderful to work overseas and to meet people from different cultures, but home is where my heart is.”
SAKKIE IN FRONT OF A TBM CUTTERHEAD BREAKING
THROUGH INTO A STATION IN SINGAPORE
Click here to read an overviev of the TBM’s journey
Click here to read more about Gautrain’s TBM, named Imbokodo