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Pūhoi to Warkworth project team draws on high flying drone data

The Pūhoi to Warkworth Project extends 18.5 kilometres along the Northern Motorway (SH1) through farmland and steep forest terrain from the Johnstones Hill Tunnels to just north of Warkworth.

The Northern Express Group (NX2), a private consortium, was charged with the finance, design, construction, 25-year maintenance and operation of Waka Kotahi NZ Transport Agency’s Ara Tūhono – Pūhoi to Warkworth motorway project.

Earthworks began in October 2017, and over the duration of the project crews will move approximately seven million cubic meters of earth from cuts to fills and disposal areas. In total, they will have built over 50 culverts of varying sizes, blasted and ripped several vertical or near- vertical face rock caps and prepared access roads and tracks.

Construction managers must quantify all earth movement to ensure work is completed per design specifications and accurate payment to crews. The conventional practice of ‘counting truckloads’ and manual surveying would be difficult and time consuming in this remote location, particularly with several hundred contractors on site.

Digital delivery

From the outset of the Pūhoi to Warkworth project, the NX2 team looked to drones to help manage and document progress on the five-year effort.

Beyond monitoring overall project progress, Haydn Bradfield, surveyor with NX2, says, “Monitoring of cut and fill is extremely important on a job this size with many sub and specialty contractors supporting the effort. It can be a challenge to quantify because we’re all working very close together. Counting trucks is inefficient and potentially inaccurate. We needed a way to check individual work areas.”

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Turns out, the scope of the work area proved difficult both on site and in the office. Survey crews needed to quickly establish ground control in the field and then develop 3D interactive surfaces.

Bradfield recalls, “It felt like we were lost in the mass of data, with no easy way to model the data quickly and effectively and then share with project managers and work crews on site.”

Midway through the second summer of earthwork (2018-2019), Bradfield attended and presented at the Trimble Dimensions user conference in Las Vegas where he had a chance to see the Trimble Stratus Software for drone mapping and analytics in action. Designed specifically for construction and resource operations, Trimble Stratus integrates drone workflows with Trimble’s Connected Site solutions to support the mapping and measuring of worksites with browser-based, survey-grade 3D surveys.

Karsten Stevenson, Key Relationships Manager at Fletcher Construction, adds, “That complete integration of ground control and visualisation simplified our workflow. We put it to work beginning in January 2019 and realised almost immediate value in terms of quick and easy access to the site surveys.”

Clouds of possibility

The NX2 survey team flies the entire site once a month to document earthwork activities. In addition to this, the survey team flies the equivalent of twice a day and sometimes more frequently for section-specific needs over the 18.5 km motorway work area.

Back in the office, one of the digital team members compares the point cloud with the design model to ensure that the cut or fill was accurate per the specifications. Any design changes or modifications to the design models are uploaded to machine control systems on the excavators and graders.

That smooth interaction between surveys and models proved invaluable information this past year as crews moved around four million cubic meters of earth across the project and began construction of seven bridges in six months.

“All road work planning starts with this data,” confirms Stevenson. “One of the first applications of the Stratus workflow was to verify earthwork volumes. From Trimble Stratus, we can quickly pull out a polygon of a site to compare with contractor earthwork movement numbers. This number is usually very close to the number estimated by the contractor. That’s been a win for us because it eliminates all questions about accuracy.”

Precision machine operations

Liam Callaghan, digital engineer at NX2 responsible for translating drone data into constructible models for the crews on the ground, points to the value of the data on specific tasks such as the detail on a rock cut. He says, “We’ll fly over the designated area, download the data and develop a working model in Trimble Business Centre that can be used by equipment operators.”

While the NX2 team has a good handle on the download of data to machines now, they are quick to say that it’s taken some time. Stevenson says, “We have so many subcontractors, each with their own pieces of equipment. One work area might have 25 machine control systems ranging over three different brands and versions of these brands, so managing that has been quite tricky because it’s such a mix. There’s every combination of machine control that you can think of on this job. Our challenge is to make sure that the right machines are in the right zones, in the right format.”

Flying new roads

Over the course of the last year, interest and use of the drone data has grown organically among the NX2 team and its many contractors.

Stevenson confirms, “Initially we showed it to two site teams who saw immediate value.”  Those site teams mentioned it to others, who asked if they could have access.

“Within a few months, we went from about 15 to 120 teams, largely contractors,” adds Stevenson. “The growing interest demonstrates to me how manual the calculation of volumes has been all these years. Now, contractors are logging into Trimble Stratus and making those calculations automatically. Those were easy wins.”

Hundreds of construction engineers and supervisors are also logging into the system to plan and check their own work progress. “What’s interesting is that the survey digital team doesn’t drive those meetings; we’ve given them all access and they’re finding ways to use the data to improve workflows and perform quality checks,” says Stevenson.

Bradfield adds, “I use it for all of my deliverables now. Contractors can run through a whole series of different costs and options, and then adjust onsite as needed to optimise work progress. And what’s great is they can actually physically see how those changes impact everything on the site, from trees to homes to connecting roads. I believe they’re making better decisions that drive the delivery of a quality product.”

Improved efficiencies

When asked about efficiencies, Callahan points to quantities and billings. “These are certainly much easier. We’ve virtually eliminated the chance of discrepancies about earth moved.  I also think it’s improved onsite decision making—our partners can make more educated decisions about work going forward because they can virtually see the results. Where we used to spend three or four days trying clarifying work to be done, we now spend about 15 minutes.”

Stevenson estimates that the NX2 digital team spends 50 per cent less time calculating volumes and more time optimising operational tasks and directly impacting the project progress and success. The value of the Trimble Stratus solution has been so strong in the last year, that NX2 is considering establishing a larger drone survey team that works with groups beyond the construction unit.

“I believe our civil and infrastructure groups can gain considerable value from this Trimble Stratus-driven workflow,” concludes Stevenson. “With easily accessible drone data, we can prepare better estimates for all our groundworks and create transparency across all project sites.”

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