Accuracy and precision paving at the highest level

The world’s most level surfaces are required at intermodal terminals being constructed in Australia. Bumps, uneven grades or accumulated water can be hazardous to the wheeled cranes that carry 90 metric ton loads (99 U.S. short tons), high and heavy, across the surface.

“Typically, asphalt is paved with rideability in mind,” said Andrew de Villiers, project manager with Boral which oversaw the asphalt paving works of the $160 million (AUD) NSW Ports’ Intermodal Logistics Centre at Enfield in South-West Sydney, Australia. “Few pavements require precision placement to design levels.”

Designers of the Intermodal Logistics Centre are well aware of the safety ramifications of uneven surfaces. Stabilizing the heavy loads is one consideration. Cargo is measured in twenty-foot equivalent units (TEUs), a reference to commonly used ship containers. The center will have through put capacity of 300,000 TEU per year moving in and out of the site.

Doing so productively and safely requires a design with a very uniform surface and a minimum slope for effective surface water drainage. This led to some very tight tolerances during the paving of the center, particularly its Intermodal rail (Terminal) section, where the heavy loads are transferred for distribution.

The desired paving tolerances had average conformance of 0 millimeters and standard deviation of 4 millimeters (0.15 inches) across an area of 92,000 square meters (120,331  square yards).

Previously, those standards would have been all but impossible to meet. However, the emergence of technology like Trimble’s 3D Paving Control System allows contractors like Boral to deliver the required results and provide a substantial boost to safety in the process.

Boral was asked to investigate new technology that might be able to meet the desired tolerances. Company officials conducted a thorough evaluation of 3D paving solutions and ultimately selected the Trimble 3D Paving Control System for the work.

“Because of the project demands, 3D Paving was discussed early on,” Andrew  said. The initial goal was to meet the tight tolerances, but Andrew said other benefits were also apparent.

“Flexibility was important due to the numerous work areas of the overall site,” he said. If paving could not occur as planned on one area of the jobsite, the crew could quickly move to another. “An entire design can be uploaded within 30 minutes,” Andrew said. The fact that no surveyors were required on the ground during paving also increased the safety of the site.

The flexibility not only kept crews productive, but also ensured asphalt that was in transit did not go to waste when plans had to be changed. The cost would have been substantial. Up to 1,150 metric tons (U.S. short tons) per day were placed.

Crucial to the process was the local SITECH Dealer, SITECH Solutions, who helped ensure a smooth flow from software design, to Universal Total Station setup, to quality control.

Meeting objectives

The objectives seemed simple enough: Place 200 millimeters (7.9 inches) of asphalt in 3 layers, provide a minimum overall structure of 635 millimeters (25 inches) from the top of the base layer, and do so evenly to prevent ponding and ensure a smooth uniform surface.

Tolerance targets were the toughest goals, with the desired result final surface average conformance of 0 millimeters and standard deviation of 4 millimeters (0.15 inches) with longitudinal grade ranged from -0.4% to -0.9%, with a cross fall up to 0.9%.

Other considerations were: 

• Eliminating human error
• Providing a productive and cost-effective approach
• Increasing safety by reducing or removing crew members from direct exposure to the mobile plant

How 3D Paving works

SITECH Solutions supported Boral by seamlessly integrating all Trimble products. Trimble’s Business Center – HCE software was used to create an un-compacted surface design to be used by Trimble PCS900 Paving Control System. This design accounts for the compaction aspect of asphalt and helped ensure a smooth final surface even when the underlying layer was “wavy.”

Business Center – HCE used the survey information of the existing condition and a compaction factor for the asphalt to create a model that yielded a smooth final surface once density was achieved by the asphalt roller.  The result was a 3D-paved and compacted surface that matched the design profile created.

The Trimble 3D Paving PCS900 Control System includes: 

• A Trimble SPS930 Universal Total Station setup on-site combined with a mast mounted on the tow arm of the paver with a Trimble MT900 prism on top and a slope sensor on the bottom for highly accurate positioning.
• A radio to communicate with Trimble SPS930 Universal Total Stations.
• A Trimble CB460 control box that displays the 3D design model and the position of the screed.

The design files are stored in the Trimble CB460 installed on the paver for guidance. This is significant, as no staking or manual leveling work was required.

Trimble SPS930 Universal Total Stations were strategically placed around the site for paving, tracking the MT900 prism as the paver moved around the Intermodal Terminal. The Universal Total Station sends position data to the paver via the radio with precise measurements (accuracy within millimeters) and compares that position to the designIf elevation corrections were needed, commands were sent through to the Trimble 2D grade and slope control system, moving the tow arms for the screed to adjust accordingly. For long paving runs, the MT900 can be transitioned to the closest Universal Total Station with the press of a button, never having to stop the machine, to ensure precise 3D positioning across the entire project.

The 3D design information was uploaded to the Trimble Control Box so the “grade checker,” who walked behind the paver, could verify that the placement matched the design.

Benefits

The system has a number of benefits in addition to meeting the tolerance specifications of the project. Among them:

• Flexibility to pave anywhere in Intermodal Terminal. With designs loaded on system, last-minute adjustments could be made and crews could still be productive.
• Design models could be generated in the office and uploaded to both paver and checker controllers in less than 30 minutes.
• Surveyors were mostly offsite.
• Reduced exposure of surveyors to the mobile plant.
• No need to work on the ground in front of the paver to re-mark worn numbers.
• The system can be implemented with current machines and can be used for operations beyond paving.
• Resources can be removed from stakeout and stringline paving and reallocated to make crews more productive.
• Utilizing the 3D system was more cost effective than paying for an extra survey crew.
• No waiting for surveyors to re-mark levels or check damaged stringline pegs.
• The system all but eliminated human error – no improper levels recorded or read, no stringlines set incorrectly.
• Precision of systems means efficient use of materials and cost savings.
• No cost for idle instruments or personnel during wet weather or extended breaks between paving.

Excellent results

When the project was finished, the lofty goals had been met. “We were able to achieve an average standard deviation of 4 millimeters across the entire 92,000  square meters on the surface lift,” Andrew  said. “We were very satisfied with this performance over such a large area.”

The results at Enfield have led to breakthrough Trimble 3D PCS900 sales for major projects in Australia, including AUD$1.5 billion Legacy Way Tunnel and Wagner new Wellcamp Airport at Toowoomba.