- SPECIAL REPORTS
- THE MAGAZINE
Underground ImprovementsThe Port of Seattle (POS) is responsible for managing Seattle's airport and marine port. Like most of our nation's airports, the POS and Sea-Tac administration have implemented significant changes in the last year to meet the growing threat of terrorism. Included in these changes are improvements to comply with new federal regulations for baggage handling and screening. At Sea-Tac, all checked-in baggage and cargo is screened underneath the airport terminal in an enormous area called the bagwell. Luggage from ticketing areas is placed on conveyor belts, transferred to and from the planes, and released for passenger pickup on conveyor belts that travel to the terminals. The new security system on the luggage conveyors involves the installation of a conveyor system with security monitors throughout the bagwell. In addition to its baggage and cargo functions, the bagwell is also the repository for all of the service lines, such as electrical and communication cables, that keep the airport operational.
The expansions and improvements at Sea-Tac include up to 30 different construction projects occurring in the bagwell at the same time. Coordination between designers and contractors is critical to the success of the improvements, especially because of the limited space available for adding new utilities. The series of HVAC ducts, FAA conduits, utility pipes, power conduits, chilled and hot water pipes, storm and sanitary sewer lines, fire protection water pipes and telecommunication lines are only some of the infrastructure elements that thickly criss-cross the ceiling and walls of the bagwell. The main terminal was constructed more than 60 years ago and many of the old utilities were abandoned in place. This has caused the design engineers and architects to compete for open areas to route utilities to and from their projects. Any significant open space has a "This space reserved" sign.
To prevent conflicts and enhance coordination among the projects in the bagwell, as-built drawings were notably needed. The first step in designing Sea-Tac's new system was to obtain an accurate as-built map of the existing features, including an inventory and audit of the existing conditions. The existing bagwell as-built drawings were a combination of schematic drawings and construction plans that spanned the airport's 60-year history. Unfortunately, these drawings were too incomplete and inaccurate to use as a base for the new designs. New as-built drawings of the area were needed that included locations of all infrastructure elements and utilities within one-half-inch of the actual position.
The area of the bagwell to be as-built encompassed more than 250,000 sq ft. It included the tunnel that runs underneath the central bagwell area; the ground floor where the baggage trains, luggage carts and conveyors operate; the catwalks above the ground floor; the second floor; the second catwalk level; and the ceiling.
Implementing 3D Laser Scanning TechnologyIn 1998, Bill White, POS survey manager, and Jim Boyd, POS senior project manager, were investigating 3D laser scanning technologies. Three years later, in the summer of 2001, when the bagwell as-built project was assigned to their schedule, White and Boyd were interested in using scanning technology with the standard measurement as-builts. They selected David Evans and Associates Inc. (DEA) of Bellevue, Wash., to conduct the work using 3D laser scanning technology.
DEA proposed to use conventional and GPS surveys to establish accurate horizontal and vertical control-a vital element to a good scanning project. DEA then used the Leica Geosystems HDS (San Ramon, Calif.) 2500 3D scanner (formerly Cyrax 2500) to collect the features in the bagwell. Notice to proceed was given in late November 2002-the heavy travel season, with 80,000 passengers a day passing through Sea-Tac airport. In addition to the mass of utility lines and cable trays, DEA also had to deal with the baggage carts, personnel and heavy activity that accompanies 80,000 holiday travelers' belongings, which all had to travel through the work area.
DEA was instructed that the airline tenants were not to be disturbed. Personnel had to work closely with the baggage handlers, luggage cart drivers and myriad personnel it takes to serve nearly 4,500 people per hour. The first hurdle was to convince the POS and airport personnel that the scanner's laser was safe for the eyes. Staring into a laser is never recommended; however, it was possible at some point in the process of the work that one of the 900 million points of data collected could be an eyeball. DEA obtained a manufacturer's certification that the Leica Geosystems HDS/Cyra Class 2 laser is eyesafe. The second challenge was to find locations for the project control that could be occupied without getting run over by baggage trains.
Setting Up ControlThe first phase of the field work involved establishing control points related to the POS datum on the exterior of the terminal. DEA performed rapid-static GPS surveys using Trimble (Sunnyvale, Calif.) 5700 receivers to establish six control points: two control points each on the southern, central and northern portions of the terminal. Using the Sea-Tac Grid Coordinate System to establish the horizontal and vertical coordinates enabled the interior as-builts to be on the same coordinate base as the exterior. Previously, the interior as-builts were not related to the area outside of the terminal.
Sea-Tac's south terminal expansion project had recently been completed and had used the column lines as control for mapping underneath the terminal. Typical production of record drawings are performed by measuring between the existing column lines. This method will not provide accurate as-built information outside of the columns. Planning a route through the maze of utilities required a more accurate as-built that would be consistent throughout the bagwell project. The utilities located in the bagwell needed to be identified in a manner that would allow them to be mapped on several levels and coordinated with the utilities outside the terminal.
Using the GPS receivers in rapid-static mode, DEA performed observations on the six new exterior control points. This established a project primary control network, which was used to constrain the terrestrial surveys going through the bagwell to the POS datum control. Traditional field survey methods were used to establish primary survey control located underneath the terminal building and within the bagwell. Using a Leica Geosystems (Atlanta, Ga.) TCR 1103 total station, initial setup commenced at one of the GPS control "pairings." By turning angles and measuring distances into the building, an interior primary control traverse was established. This control was permanent and out of the way of traffic.
Precise elevations were obtained for each primary control point by performing a differential level traverse using a Wild NA 2000 digital level. This level work was conducted as a separate task to establish and maintain vertical integrity between points, which yielded more precise results than could be obtained by a total station measuring vertical angles. Similar to the horizontal control procedures, the levels started at the initial GPS control pairings and continued throughout the interior. The level loop continued until it closed upon the initial point at the beginning of the loop.
Using the primary control as the base line, secondary control was set for the interior mapping. DEA constrained and adjusted this secondary control to the primary control values using the same procedures. The secondary control also tied into existing control points set by previous contractors and design teams. Connecting these ties to the others' horizontal and vertical control enabled POS personnel to relate the new as-built surveys to the current construction. Control was set, as much as possible, out of traffic areas since the baggage trains and carts were a constant and continual issue with all phases of the work.
Scanning with AccuracyWith control set, DEA used the 3D scanner to collect the features in the bagwell and to accurately locate all visible features. Each single scan contained 1,000,000 data points, or point clouds. The accuracy within a single scan (1,000,000 points) is one-eighth inch. More than 900 scans of point clouds were tied together with the survey control, enabling DEA to achieve a mapping tolerance and an overall accuracy of one-half inch.
The POS has a database of Sea-Tac's existing utilities; the system uses numbers to identify the type and size of each utility. In the bagwell area, POS personnel manually inspected and tagged each pipe, wire bundle, tray and conduit that was 2 inches in diameter or greater. The data collected on each utility noted the type of utility, size, status (active or abandoned), and the owner or carrier, if known. This information was included on the first draft 2D drawings; the inventory was input to a database and the identifier was imported into the CAD drawing. The project required more than 2,000 separate layers to identify the various utilities.
Mapping the BagwellOnce the scans were registered, adjustments completed and scan data processed and proven, DEA began the interior as-built mapping procedures. Leica Geosystems HDS Cyclone software (formerly Cyra Cyclone) enabled the team to use the scan point clouds to identify and model pipes and conduits, wire trays, baggage conveyors and motors, junction boxes, control cabinets and more. The line work and modeling were imported into AutoCAD for production of the final drawings.
DEA produced draft maps, which were used for field walks as portions of the work were completed. During the field walks, the draft copies were red-lined and corrected, and dimensions and utility identifications were verified and checked for conformance to the actual features. The draft maps included the numeric identifier from the utility inventory database. This enabled the quality assurance person to verify the size, type and location of each utility and to confirm that the unique identifiers were correct.
Continuing BenefitsScanning Sea-Tac's bagwell allowed DEA to create accurate maps of the existing utilities and reduced the potential for interferences during design work at the airport. The new comprehensive as-built drawings allow designers and contractors to easily locate existing utilities. Scanning captured all of the features and, by saving the scanned data, even the features not mapped can be mapped at a later date. As the improvement projects at Sea-Tac continue during the next five years, the designers and contractors working on the airport will continue to profit from the as-built maps. The newly created model will reduce change orders and schedule impacts by allowing designers to check clearances and interferences with existing utilities. By combining older and newer technologies, the Seattle transportation hub will be able to advance its operations for another 40-plus years.
More information and updates on the progress of the Sea-Tac airport expansion can be found on the Port of Seattle website, located at www.portseattle.org.