WorldWide Drilling Resource

Longest Railway Tunnel in East Africa Compiled by Caleb Whitaker, Associate Editor WorldWide Drilling Resource ® The Ngong tunnel in Kenya is part of the Standard Gauge Railway (SGR), which is under construction from the Kenyan capital of Nairobi to the town of Naivasha. China Communications Construction Company (CCCC) drilled a nearly three-mile-long tunnel in Ngong, Kajiado County, which has been designed as a single-track railway tunnel with a clear- ance height of about 30 feet and a width of over 20 feet. The tunnel became the longest rail- way tunnel in East Africa and second longest in Africa. CCCC engineers used the New Austrian Tunneling Method (NATM) of drilling and blasting to build the tunnel. This was the first time the method had been used on such a large scale in Kenya. In the world of tunneling, the NATM is widely seen as a series of principles which allow for a more dynamic assessment of the terrain. Some prefer to use names such as Sequential Excavation Method or Shotcrete Method to describe the proccess. Unlike classical methods, such as the Belgian or German ap- proaches where the tunnel is immediately supported without allowing it to deform naturally, NATM allows the deformation of the rock mass before stabilizing the tunnel. This reduces the amount of additional support materials required. The resulting tunnel is covered with a layer of sprayed concrete or shot- crete, which is faster and easier to execute. The shotcrete layer increases the internal cohesion of the rock mass, reinforcing the support ring, and can act as a temporary or final lining, depending on the site’s requirements. The method works by mixing construction with settling-in periods. During settling-in periods, rock mass is observed, allowing the tunnel sup- port design to be adapted based on the geological requirements. The method is economical, efficient, controls surface collapse effectively, and enhances the working envi- ronment during construction. For the Ngong tunnel, it took two years for 600 workers and engineers to complete the tunnel, battling water leaks and uneven pressure, while tak- ing care to protect an oil pipeline. The tunnel was constructed using the three-bench seven-step excavation method. Blasting was used to create the tunnel’s arch shape. Among the tunnel’s features are 146 refuge holes for maintenance workers to shelter in when trains approach. An emergency rescue channel was also built with- in the tunnel, to allow for vehicle access in case of emergencies. Six jet fans will be installed to ensure ventilation once the tunnel is operational. Photos courtesy of China Communications Construction Company. EXB New & Used Bits, HDD Bits & Tools, Drag Bits & Wings, Bolt-On Drag Bits, Reverse Circulation Tools, Hole Openers, Claw Bits, Stabilizers, Subs, Custom Tooling & Welding, Hammer Bits, Drill Collars, Pipe Wipers, and Drill Pipe. Office: (661) 834-4348 Rod Henderson / Eran Henderson 661-201-6259 • 661-330-0790 sales@bitcobits.com www.bitcoinc.us 26 JANUARY 2019 WorldWide Drilling Resource ® Time for a Little Fun! Win a prize! Send your completed puzzle to: WWDR PO Box 660, Bonifay, FL 32425 or fax to: 850-547-0329 Can you identify which ads in this issue these two photos came from?