30 Days to Deliver: Expanding Capacity at an Active Airfield
Fusing mobile lidar, subsurface utility engineering (SUE), and conventional survey at Dyess Air Force Base to support engineering design
The taxiway at Dyess Air Force Base was in need of expansion, and also plagued with hydraulic issues. USACE was engaged to solve the engineering problem rapidly, and Continental Mapping was brought in to provide high accuracy surveying and mapping in order to support an accelerated project timeline.
Located near Abilene, Texas, Dyess AFB serves a critical role in the local economy as well as a front-line role in global military operations. Dyess AFB is home to the 7th Bomb Wing, a premier unit of B-1B Intercontinental Bombers. The unit also features an important C130 Air Mobility Command (317th Airlift Group) with the largest fleet of J-model (modern) C130s in the country.
Dyess AFB flies and maintains 33 B-1B bombers and 28 C130s. The intense weight of these machines (B-1B bombers weigh 95 tons without cargo) requires proper runway and taxiway design to support them. Increases in activity and fleet size have pushed existing taxiway and runway infrastructure to the limit. Based on that, the base and the US Army Corps of Engineers identified the need to expand the taxiway.
To support this expansion, Continental Mapping was tasked to complete high accuracy survey and mapping of the taxiway and surrounding surfaces. Critical project requirements were:
- Complete the surveying and mapping within 30 days to minimize impact on the base and expedite the design and construction process
- Complete a high accuracy topographic survey of the taxiway
- Locate all above ground assets
- Locate the expansion joints for the hundreds of concrete slabs
- Locate all underground utilities
- Survey all the grassy infield surface adjacent to the existing paved taxiway
To meet these requirements, Continental Mapping used several technologies with sophisticated data fusion workflows to provide engineers with a full 3D model of the existing conditions. Those technologies were:
- Mobile lidar to efficiently and accurately gather an extremely dense point cloud of the taxiway and surrounding grassy areas
- Mobile lidar was acquired on a weekend afternoon to minimize interruptions on operations, and driven at a very slow speed (~5 mph) to ensure optimum density of the point cloud
- Several Subsurface Utility Engineering (SUE) techniques were used to locate sub-surface utilities like water and fuel lines, storm drainage, and navigational electric
- Conventional survey techniques were used to set permanent monuments, provide control for the mobile lidar acquisition, confirm existing as-builts, and collect data on any other above ground assets of interest
Continental Mapping delivered a comprehensive 3D survey, including locations of all existing assets above and below ground. Positional accuracy of surface features were located at 0.1’
USACE and Dyess AFB set a goal to complete design within 60 days. A firm window of 30 days was allotted to Continental Mapping to complete all surveying and mapping.
Imagery acquisition on the base was forbidden due to national security reasons. This limitation complicated the project as ground-based imagery helps match up the point cloud to existing features and provides context to the lidar analyst during feature extraction. Aerial imagery in Google Earth did not provide enough detail and was out of date.
Dyess AFB was justifiably concerned about who was physically accessing the base. They needed precise coordination and attention to detail to allow the right staff on the base so as not to interfere with base activity or national security.
Challenges met — with speed, efficiency, and communication
Mobile lidar provided the team the ability to get on and off the base very quickly (half of a day for collection). The support of Dyess AFB Civil Engineering Office personnel was also critical to assist in facilitating access and coordination.
Leveraging SUE technologies to locate subsurface utilities in and around the taxiway was a critical component of the overall survey effort. Continental Mapping used different SUE protocols to complete the subsurface survey. The first approach was a vacuum truck, which used a combination high pressure air and water to excavate. Unfortunately, the dense clay soils prohibited the efficient digging of test holes to any significant depth. Alternatively, Continental Mapping used electronic tones to determine the depths and locations of underground utilities and compared that to existing as-builts. This approach was vetted and agreed upon by the client and noted on the plans. The efficient adjustment of technical methodologies is often critical to meeting project requirements on time and within budget.
Continental Mapping utilized strong leadership and logistical coordination to define the project work flow to meet the client expectations.
- Coordinated all survey teams to obtain access to the site and complete safety training
- Contingency plans were developed for any project delays such as weather or base specific issues
- Provided real-time responses to client’s design-team edit comments during production phase of the project
Fusing the mobile lidar, subsurface survey, and conventional survey was essential in delivering a fully integrated, 3D dataset.
- Integrated 3D data from mobile lidar feature extraction, field survey and subsurface survey
- Leveraged the strengths of each acquisition method to provide a best of breed dataset
Proper survey control allowed for high accuracy surface feature extraction from the point cloud at a positional accuracy of 0.10’. In addition, the extremely dense point cloud acquired from mobile lidar allowed for the delineation of each of the 25’x25’ concrete slabs and above ground assets. This information was highly desirable by Dyess AFB engineers and would have been extremely time intensive to collect via conventional survey methods.