Warzone drainage project closes out Oct 2011
Desiree Willis, Technical Writer, The Robbins Company
- Rocket strikes and unexploded ordinance buried in the bore path were just two of the possibilities facing the team operating a Robbins SBU at Bagram Airport in Afghanistan.
Bagram Airport culvert breakthrough
- High winds, dust clouds and temperatures exceeding 100° F were also regular occurrences during the excavation of a 128m long crossing below the taxiway at the US Air Force base in occupied Afghanistan.
- The crossing is part of an extensive drainage plan designed by C2HM-HILL for the US Army Corps of Engineers. When rain or runoff from the snowy mountains surrounding the airport drain into the valley the dry clays do not absorb the water, leaving potential hazards around the 3.2km long runway. The Kilo Culvert will divert water into nearby Coyote Creek, while the planned Russian Culvert will in turn divert the creek further away from the strategic military base.
- A crew of three Robbins field service personnel was onsite throughout the project, assisiting Turkish sub-contractor Yuksel in the construction of the crossing below the runway.
- "We launched the machine in less than a month. They swept the area for mines prior to construction, but detection is only accurate to about 4ft deep, whereas our bore pit was 10ft deep," said Scott Fisher, Field Service Consultant.
Runoff from surrounding mountains affect Bagram's runway
- 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 48in (1.2m) diameter SBU-M with a soft ground cutterhead. 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.
- The Robbins SBU-M was continuously steered to the specified .05% downgrade from an operator’s console inside the rear shield.
- At machine launch, the SBU-M was bolted to the lead steel casing. An in-shield motor and drive train provided torque to the cutterhead, while forward thrust was provided by the ABM. Muck was continuously removed through an invert auger inside the casing.
- "When the machine holed through, the bore was surveyed and it finished only 0.2in (5mm) low and 1in (25mm) to the right over 400ft," said Matt Weaver, the Robbins Field Service Technician. The specifications for the project stated a much larger allowance of up to 4in 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.
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