At the CCNZ conference last year, Edward Kelly from Fulton Hogan presented a case study on using an unmanned aerial system (UAS) for project work on the Huntly section of the Waikato Expressway.
The ‘Huntly Section’ is a 16-kilometre four-lane motorway construction contract with an estimated cost of $320 million. This is one of the final links in the completion of the Waikato Expressway, linking the two cities of Auckland and Hamilton in the North Island.
Earthworks involves moving 3.2 million cubic metres of cut and fill through difficult terrain, including large sections that require preload, hence timely volume assessment is critical for programme status and forecasts.
To keep up regular updates on the progress of the dirt shifting of this huge project with its steep and slippery batters, the survey team used a UAS as a survey tool to measure and process earthworks quantities in a timely manner.
So effective was this technique that a single survey crew was able to produce a volume report for the entire 16-kilometre project site within a week, including flight time. Traditional surveys, says Edward, would take four survey crews a week to complete the fieldwork, and another to process.
The team decided on a fixed wing RTK MAVinci Sirius Pro after a lot of research. “The reason we went to the fixed wing is we could get a greater flying time, at time of purchase. A drone would only give us a 10-minute flight time, whereas the fixed-wing provided a full 50 minutes of actual survey time.”
The survey team spent four days training, which involved three days practical site training and one day going through Civil Aviation Authority (CAA) regs and rules. They also did a two-day Remotely Piloted Aircraft Systems course at Massey University School of Aviation, which involved the likes of reading aeronautical charts and radio protocols.
“I highly recommend this course; it gave us a total overview and increased everyone’s knowledge of aviation requirements.”
Then they applied for Part 102 CAA Certification and sought permission from the NZTA and Waikato District Council (they were required to fly across WDC roads, but not along them).
Although the flights can be performed by a solo surveyor they made the call to make it a two-man operation for safety reasons, and use a ‘spotter’ when required.
Other equipment included a GPS base station and a Panasonic Tough Pad, office PC, photo processing software and AGTEL forecasting. The processing computer cost $15,000, says Edward, as they need something really grunty.
In the field the unmanned aerial vehicle (UAV) is assembled and the base station set up, which takes about 10 minutes. A flight plan is created and programmed to the UAV.
The pilot and the assistant have a list of individual checks that they do before the UAV is hand launched. “Once that happens off she goes in a fairly simple exercise. In the meantime the assistant will be monitoring the tablet and he’ll be relaying messages to the pilot all the time – how much battery has been used, etc.
“This saves the pilot taking his eye off the plane, and we are fairly strict on keeping a constant eye on the unit.”
In the early days, says Edward, they flew grid flights over large areas (59.2 hectares) of the site, which took about 48 minutes. “After five months the suppliers of the plane came up with the corridor mapping that only required selecting the centre line of the corridor we’re going to fly and the corridor width that we wanted to cover.”
This resulted in less distance (21.1 kilometres), a smaller area (35.3 hectares), faster processing times and better results.
Landing the machine got easier as the project progressed and they could use the alignment as a landing strip.
“We discussed the flight with the guys on-site and when we came into land we would get hold of them on the radio and they just stopped production for literally two minutes, so downtime for the construction crew was down to a minimum.
“As a quality control we would also measure random GPS points on areas flown to use as a comparison to the processed flight surface; normally a five or 10 minute exercise.”
There was only one mishap when the plane flew into neighbouring Taupiri mountain through a system error, but there was minimal damage, although the camera had to be replaced at a cost of $5000. The plane is programmed to fly automatically back to base if it goes out of range within 100 metres.
Data processing takes about 10 minutes with cropping the chosen area and removing the artefacts. Water is an issue, says Edward, “as the software doesn’t like big puddles so we remove the water to eliminate any sort of redundancies”.
The detail and accuracy of the data has also settled any disputes and claims over ‘volumes’ of shifted dirt very quickly, says Edward.
Obviously the most important aspect of this method of site surveying is savings, he iterates.
“Traditional surveying would take us 2600 surveying hours per annum and now we are looking at 1110 hours, so that’s a 58 percent saving on labour which is massive on any construction project.”