Afghan SBU Flies Below Bagram Airfield
September 29, 2011
The 420-ft (128-m) long crossing is below the taxiway at Afghanistan’s Bagram Air Force Base. The crossing is part of an extensive drainage plan designed by CH2MHill for the Army Corps of Engineers. When rain or runoff from the snowy mountains drain into the valley occupied by the base, the dry clays of the area do not absorb the water, leaving potential hazards around the two-mile (3.2-km) long runway. The Kilo Culvert will divert water into nearby Coyote Creek, which will be further diverted off the base by the planned Russian Culvert.
Field service personnel managed the setup, maintenance, and operation of the SBU-M and auger boring machine (ABM). Due to the very dry clay material with little rock, Yuksel selected a 48-in. (1.2-m) diameter SBU-M with soft ground cutterhead–other types of cutterheads are available for both hard rock and mixed ground conditions. The specialized soft ground head was designed with tungsten carbide bits and large muck openings for a smooth flow of material. If rock was encountered, the openings allowed for access to the cutterhead to change the tungsten carbide bits to disc cutters while in the tunnel.
“I worked on the project every day for six weeks, and I was able to double production to 5 in. (130 mm) per minute. When the machine holed through, the bore was surveyed and it finished only 0.2 in. (5 mm) low and 1 in (25 mm) to the right over 400 ft,” said Matt Weaver, Robbins Field Service Technician. The specifications for the project stated a much larger allowance of up to 4 in. off line and grade. Crews will now perform grouting in order to minimize settlement below the runway, and will install reinforced concrete pipe as the final liner.
This article was supplied by The Robbins Co., based in Solon, Ohio.