Infrastructure: One runway coming right up

1 August 2007

By John Clucas

In a joint US/Australian military exercise, Trimble machine guidance equipment was behind the astonishingly fast construction of a Northern Territory airstrip that is able to handle a C-17 without a care in the world.

The US Army prides itself on the speed with which it can defeat an enemy. In fact, speed goals established by the US Department of Defense (DoD) call for the US military to deploy to a distant theatre of war in 10 days, defeat the enemy in 30 days and be ready for the next fight within another 30 days.

Fast construction of new airstrips is vital to this timing; earthmoving machines are vital to the construction and guidance equipment is vital to the machines.

To fine-tune its airstrip construction skills, DoD’s Engineer Research and Development Center (ERDC) runs a Joint Rapid Airfield Construction (JRAC) Program.
The program for June 2007 included construction of an airstrip in virgin bushland at the Bradshaw Field Training Area, about 600km southwest of Darwin. The work was carried out as a joint US/Australian military exercise.

The airstrip was structurally designed to accommodate 500 passes of a 265 tonne C-17 cargo aircraft and just two weeks were allocated to:
• remove the trees, grub the 42,000 square metre site and remove sandstone boulders,
• grade the area to design elevation and prepare the subgrade,
• place and compact two 150mm layers of granular material meeting the specific gradation requirements for the C-17 aircraft, and
• form drainage channels to handle the intense rainfall typical for the region.

To assist in selecting the best site, JRAC used advanced terrain analysis and material performance prediction methods to minimise the engineering effort. Site surveys were conducted using Global Positioning System (GPS) tools and laptops loaded with geospatial software.

JRAC also used its Rapid Assessment Vehicle Engineer (RAVEN) to gather topographic data. RAVEN is based on the Bobcat Toolcat utility vehicle. It has several implement attachments that can be used on the front of the vehicle and is equipped with the Trimble Real Time Kinematic GPS system that gathers topographic data with centimetre accuracy in rapid time.
RAVEN can be operated by a user in the cab, by remote control or through autonomous mode if an area is deemed too dangerous for soldiers.

Once the topographic data was collected, soils were analysed in the field using a rapid soils assessment kit developed by ERDC.

In order to achieve the required pavement strength in such a short time, JRAC has in its arsenal rapid soil stabilisation techniques such as fibre-reinforced multi-purpose matting and combinations of fibre or polymer with high-early strength cement.
The taxiways and aprons in this project were stabilised with a combination of high-early strength cement and fibers.

Trimble’s Terramodel Software was used to create 3-D designs which were transferred to earthmoving equipment fitted with machine guidance/control instrumentation.
Using Trimble’s Site Vision Office software and wireless links to the machines, the earthworks supervisor in the office was able to track machine locations and monitor cut and fill requirements.
In addition, clicking on any specific vehicle icon on his computer screen showed that machine’s idle time and communications status, or provided a view of the screen in the machine’s cabin, as the operator saw it.

The US military set up its own Trimble GPS base station and initially planned to fly in its own fleet of earthmoving equipment fitted with Trimble GCS900 grade control systems.
As it turned out, Australia’s Department of Defence (ADD) supplied the earthmoving fleet of five dozers, seven graders and five scrapers fitted with Trimble GCS900 grade control systems, plus another dozer and five rollers fitted with Caterpillar’s AccuGrade system.
In addition, ADD’s survey crews used three Trimble SPS880 rovers.

From the US, two Terex RS 325 reclaimer/stabilisers and one dust control sprayer mounted on a High Mobility Multipurpose Wheeled Vehicle (Hummer) augmented the Australian fleet.

With sixty operators swapping in and out of machines, some night work and Trimble technology guiding the whole process, a job that would normally have taken three months was completed in just two weeks.

After completing the airstrip, the JRAC taskforce worked 24/7 over four days to construct aprons and taxiways before the project’s grand opening, when VIPs arrived in a C-130 Hercules aircraft to witness two C-17s land successfully and park on the new aprons.

The airfield fulfills the Australian Government’s requirement for a facility to support ever increasing air traffic in the region.