This article was written by Manuel Hernandez with input from Jack Mesojedec of SWA of Palm Beach County and our President / CEO for WasteCon 2008 in Tampa, FL.
GPS CONCEPT SAVES TIME AND MONEY IN LANDFILL CELLS CONSTRUCTION – A CASE STUDY
Manuel J. Hernandez
Project Manager CDM
West Palm Beach, FL
Ken Rogers
Project Manager
CEC
Jack A. Mesojedec, P.E., BCEE
Solid Waste Authority
West Palm Beach, FL
ABSTRACT
CDM and CEC, under contract to the Solid Waste Authority (SWA), recently completed the construction of two, 10-acre landfill cells in record time by using the latest Computer Aided Design (CAD) and Global Positioning System (GPS) software and equipment. CDM was the design engineer for the 20-acre municipal solid waste (MSW) landfill lateral expansion. The design plans were prepared using the latest AutoCad Civil 3D software to provide the contractor a detailed model that could then be transferred into the GPS system which was used to perform the grading of the cells. From this 3D model, CDM prepared a grid system, which consisted of a series of points with GPS coordinates (northing, easting, and elevations) which defined the grades within the cells. The 3D model and grid system was then turned over to the contractor, CEC, to transfer the information into their GPS Machine Guidance and Automation software. CEC’s grading equipment is outfitted with a laptop that contains the 3D model and the corresponding coordinates and guides the operator during the grading operation. This GPS grading software allowed the operators to commence grading of the cells without the need to perform the initial staking of the site, which would otherwise have taken between 4 to 5 days. The grading of the cells was also performed within considerably less time using the GPS software than the traditional staking methods. The 3D model and coordinate point system also proved to be an essential part in expediting the required engineer certifications so that the contractor could continue with each subsequent phase of the project, such as the placement of the liner system, leachate collection piping, and the protective cover layer. Since a data table had been created from the 3D model, it was easy to add the contractor’s surveyor as-built information to verify that the required design parameters had been achieved. This project was a demonstration of how engineers, and contractors can team together, using advanced technology, to deliver a quality project, while saving the client time and money.
INTRODUCTION
The Solid Waste Authority of Palm Beach County (SWA) owns and operates an integrated solid waste management system at its North County Resource Recovery Facility (NCRRF). The NCRRF is comprised of Class I (MSW) and Class III (C&D) Landfills, a waste-to-energy facility, yard waste processing facility, composting facility, hazardous waste facility, and material recovery facility. The SWA has aggressively managed the timely design and construction of new landfill cells to meet the needs of the county’s solid waste generation. To accomplish this, the SWA has implemented a phased approach to cell design and construction. In 1998, CDM prepared the permit design package for the Class I Landfill cells 9 through 16. The design consisted of a “saw tooth-shaped” leachate collection system (LCS), a double 60-mil high density polyethylene (HDPE) liner, a composite geonet drainage layer, and nine 6-inch’ HDPE lateral leachate collection pipes, which transport leachate by gravity to an 8-inch’ HDPE manifold pipe. This upfront permitting of eight cells allowed the SWA the flexibility to expand the landfill as needed. On average, the SWA has been constructing two, 10 acre cells every 2 to 3 years to meet their solid waste disposal needs. A total of 14 cells have been constructed so far at the Class I Landfill. SWA has been following the traditional design, bid, build process for the required expansions to the landfill. Even though the Class I Landfill cells 9 through 16 had been designed in 1998 as part of the permit application package, CDM was retained by the SWA to update the design and specifications of the required cell expansions before bidding and construction of each pair of cells. The updates included slight changes in grading of the cells, leachate collection system pipe sizes, and new liner, geonets, and geocomposite materials. During the first half of 2006, CDM performed the design update for the Class I Landfill cells 11 and 12. The project was put out to bid during September 2006 and a contract was awarded to CEC on November 2006. At the commencement of the project, CEC indicated that they had been using GPS guided equipment for some time and requested a 3D model of cells 11 and 12 from CDM that they could use with their equipment. During the months of January and February 2007, CDM worked closely with CEC to develop the 3D model based on the design plans.
3D MODEL FOR CELL GRADING PLAN
During the second half of 2006, CDM transitioned from Landdesk to AutoCAD Civil 3D as the main drafting and design tool. This transition proved to be key in working with CEC to prepare a 3D model that could be imported into their heavy equipment GPS system. The first step in creating the 3D model was importing the design into AutoCAD Civil 3D. Once in AutoCAD Civil 3D, CDM proceeded to creating a coordinate point system throughout the cell’s subgrade that would allow the contractor to grade the cells using their GPS equipment. The coordinate point system developed conformed with the project specifications, which required that the contractor provide an asbuilt survey of the cells subgrade, processed sand protective layer, leachate collection and leachate detection pipes, and top of the 2-foot protective cover at a frequency of every 50 feet along the low points and high points of the cells “saw tooth” configuration. The coordinate point system was comprised of approximately 800 points which consisted of northings, eastings, and elevation along the cells subgrade. Figure 1shows the cell plan view with the coordinate point system developed, and Figures 2 shows the point table developed for the site.
GRADING THROUGH GPS GUIDED EQUIPMENT
Once CDM was satisfied with the 3D model and the coordinate point system, the information was transmitted to CEC. For the construction of cells 11 and 12, CEC used grading software developed by Agtek®. This system creates a 3D model that can then be used with GPS equipment mounted on machines such as motor graders, and scrapers to provide operators a clear representation of the jobsite with accurate grade information, anywhere on site. The combination of the 3D model software and the GPS receivers mounted on the grading equipment allow the operators to guide the machines to the required final grade with great accuracy and efficiency. An interface between the control system and the machine’s hydraulics can also be implemented to automatically position the blade as the final grade is approached. Through the use of the 3D model and the GPS receivers, CEC was able to commence the grading of the cells without an initial staking of the site..In addition, this approach reduces the staking required during the grading and construction of the cells.
REDUCED SITE GRADING SCHEDULE
Three years prior to the construction of cells 11 and 12, the SWA had completed the construction of cells 9 and 10, which were also 10 acres each and had a similar “saw tooth” design. The pre-liner earthwork for cells 9 and 10, which consisted of grading the cells subgrade and placing and fine grading the 6-inch processed sand protective cover, took approximately 83 working days. On the other hand, the pre-liner earthwork for cells 11 and 12 was completed in less than a third of the time required to complete cells 9 and 10, or approximately 25 working days, with the help of the 3D model and the GPS system. Grading of the cells with the assistance of the GPS system also proved to be precise. The project design allowed the contractor a tolerance +/- 0.1 feet on “saw-tooth” grades. Actual grades were consistently achieved within the allowable tolerance and the required slopes. The combination of the 3D model and the GPS system also helped reduce the physical surveying and staking activities required with traditional grading activities. It is important to point out that the means and methods for the cell grading implemented by CEC were also different from those of the contractor for cells 9 and 10. CEC’s approach to grading of the subgrade was to have a flat subgrade and create the “saw tooth” shape with the processed sand used for the 6-inch thick screened subgrade directly under the liner system. This was viable since the fill material to be used for the common fill met the specifications of the 6-inch processed sand layer. The material was also provided by the owner free of charge.
EXPEDITED ENGINEER CERTIFICATIONS
CDM specifications required that the contractor certify that all lines and grades have been constructed in conformance with the contract documents prior to proceeding with subsequent lifts, layers or backfills. As a result, the contractor is required to provide as-built data and surveys to substantiate the certification. This task was simplified due to the fact that the 3D model was prepared along with the coordinate point system used for the grading of the cells. Upon completion of the various lifts, CEC would submit as-built information, in table format, for all the coordinate points. Since the data was provided side by side with the design information, it was easy for the engineer to verify that the required elevations and corresponding slopes had been met by the contractor. CDM’s turn-around time for certification of the requested lift or layer was usually within a day after the data was submitted by CEC. This turn-around time allowed CEC to proceed with the construction of the cells efficiently. Figure 3 shows an example of as-built information submitted by the contractor’s surveyor and Figure 4 shows a sample spreadsheet model used by CDM to certify compliance with the cell design and required slopes.
CONCLUSION
The successful and efficient completion of the construction of SWAs Class I Landfill cells 11 and 12 was accomplished through close coordination of CDM and CEC in creating a detailed 3D model that could be used with CEC’s GPS grading equipment. The precision and accuracy of the GPS grading was impressive and the benefits of using the system were evident in the reduced construction time, reduced physical surveying activities and continuation of subsequent construction activities. The results were such that SWA, CDM, and CEC proceeded to designing and constructing two additional cells at the Class I Landfill shortly after the completion of cells 11 and 12. The working relationship between the engineer and the contractor was beneficial to the owner not only in delivering a quality project in record time, but also in minimizing change orders, improving communications and decision making, and maintaining a positive working attitude among all parties.
