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Home arrow Archives   The American Surveyor     

Road Scholars Print E-mail
Written by Larry Trojak   
Saturday, 08 March 2014

Adding IP-S2 scanning technology, APAC Tennessee meets challenging survey demands on eight-mile road job

A 2.392Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

The phrase "necessity is the mother of invention" is generally used to describe someone's unconventional approach to solving a vexing issue--in current terms, how they thought outside the box. For APAC Tennessee, necessity was calling very loudly on a recent Arkansas highway reconstruction project. Faced with one of the more challenging deadlines for completion in its lengthy history, the company needed to choose between bringing survey crews in from other projects or finding an alternative method to tackle its initial survey needs. It opted to use mobile LiDAR scanning--a method it had been considering for some time--on the entire 8.5 mile project, giving them the data needed to meet their survey demands. Doing so not only got that job done quicker and far more efficiently, it improved their competitive position for future bids and opened the door to new uses for the technology.

Incentive to Change
The project that brought about such a dramatic shift at APAC Tennessee was an 8.5 mile reconstruction job for the Arkansas Highway and Transportation Department (AHTD) on Interstate 40 between Little Rock and Memphis. According to Jim Smith, APAC Engineering Manager, the project not only had some unique demands attached to it, it was also laden with both incentives and penalties.

"This job is challenging in so many ways," he says. "First, there is a $100,000 per day `disincentive' for not meeting the project deadline, as well as a $100,000 per day incentive for getting done early. There were also some interesting twists to the profile segment of the survey which almost dictated how we tackled the job. We knew that the logistics of getting things surveyed, getting the information in here, getting things moving, and so on, were going to be tough; there simply wasn't any room for a delay in any part of the process."

Smith says they've done scores of jobs which were survey-intensive before. But he knew that, on this one, dedicating the amount of manpower needed to keep the survey function on track would adversely affect other jobs within the division--not an option they liked.

"When we considered what was needed to get the initial layout, the intermediate surfaces measured and so on, we just felt like we had to look past conventional surveying," he says. "Just this past year we had switched to stringless paving and added machine control to many of our graders and pavers, so we were aware that laser scanning was an option available to us. Initially, we were thinking more about static scanning than mobile LiDAR, but we'd heard a good deal about the potential uses for mobile LiDAR. So we contacted Earl Dudley & Associates, the Topcon scanner specialist for this area, and had them show us how Topcon's IP-S2 Mobile Mapping System could work for us."

Proof is in the Piles
To test the feasibility of scanning in their operation, Smith and his colleague, Jerrad Burns, had Dudley's crew visit them at APAC's Memphis location which is one of the company's larger aggregate storage sites. Because inventorying stockpiles (both by-project and quarterly) is a regular function of the company's survey crews, it was decided that using the IP-S2 to scan the existing piles would be ideal to see its capabilities.

"This was important for us for a number of reasons," says Burns. "First, stockpile inventory is a fairly labor-intensive process, which means we have to pull surveyors off other projects to do it. If we could scan the piles and quickly gather accurate inventory, we'd be ahead of the curve in terms of both efficiency and safety. Second, with the road job looming larger, we knew we wouldn't be able to afford pulling crews from that job to do inventory. This was a huge test for the technology and it immediately impressed us. One 40-minute driving session around the piles yielded more data than what a crew of three or four working a day and a half could compile. We knew we were on the right track."

He adds that, not only was the time savings impressive, when the IP-S2's scan results were compared to those done using traditional survey techniques, a slight--but still significant--disparity showed.

"I went out and, using a total station, shot 80 to 90 points. After I did my volumes, I saw that the LiDAR figures were about 2% lower than mine, the result of my conventional survey shots having bigger voids than those of the IP-S2," says Burns. "While 1% or 2% might not seem like much, when you consider we regularly inventory over a million tons of material each quarter--and pay an inventory tax on--those savings can be impressive."

Profiles in Quality
Burns says their initial thought process had them using LiDAR just for originals and finals on the road project. But, after seeing the degree of speed and accuracy they were getting on the stockpile scans, they began to consider the feasibility of doing profiles. Once again, they consulted with the Earl Dudley team, seeking advice on the matter.

"By this time, work on the job had already started, so the pressure was really on," says Smith. "The Dudley crew instructed us on how to place survey control reflective targets for the LiDAR and came out and helped us start scanning the original profiles."

Because the road being reconstructed originally consisted of 9" of asphalt, placed over an existing concrete roadway, APAC was thrown a bit of a curve by AHTD's engineers.

"They said the specification required that we profile the concrete below, not the existing asphalt," says Smith. "So we needed to mill off eight miles of asphalt and gather profiles of that concrete below. It became apparent that the IP-S2 was going to have something of a baptism by fire. We broke the job up into five segments and as soon as one segment was milled and cleaned up, we would establish control and set down targets every 1,000 feet, with millimeter points every 400 feet for verification, and run the LiDAR. Doing it in this way, we got the full eight miles milled off in ten days. As to the data collection, we figured it would have taken two full crews somewhere between two to three weeks to gather eight miles of data. By comparison, one person did the full eastbound and westbound sections in a total of four hours. This made all the difference for us."

Screen Time
With the data gathered, the onus fell to Burns to begin post-processing and extraction of critical info to create a deliverable product. Their workflow consists of downloading the data from the IP-S2, post-processing with Topcon GeoClean software and exporting an LAS file to Virtual Geomatics software.

"Inside Virtual Geomatics we then convert the data to State Plane Coordinates, tie down the LAS data with our existing control, and then export a DXF file which can then be opened in AutoCAD or Carlson Software," says Burns.

While Burns admits there is a bit more post-processing to address than in the past, he is equally quick to point out that the data derived from that effort is invaluable.

"Doing this conventionally, our cross sections would be 25 to 50-feet; now we could take a cross section every foot if we needed to. Because we have more data to work with than we ever could have imagined, the quality of our deliverable product is that much better."

Calculating the Savings
Both Smith and Burns are quick to point out that adding the IP-S2 will result in direct, bottom-line savings--but quantifying some of that will not be easy.

"On this job alone it would have taken two crews two weeks to do what one surveyor and I did in a week with LiDAR," says Smith. "So that's a time savings of one week, which, for us, can be seen as $500,000. That's significant, but it runs so much deeper than that. For example, we are always having a tough time finding good surveyors that know our business. This is a great way to use the technology to our advantage and offset that problem. Also, because we had the IP-S2, we did not have to pull people off of other jobs to keep the pace up on this one. As a result, none of those other projects suffered so that this one could succeed."

That same "wise use of personnel" message resounds in the inventory practice as well, he adds. Instead of having four men climbing piles for a week and risking injury to get shots, one man can scan the piles in 40 minutes and those other men can be racking up five days of production elsewhere.

"We've already identified so many uses for this technology," says Smith, "and we're just starting to get comfortable with it. But quantity verification is definitely one area we like. Sometimes customers like state DOTs use old plans; they often don't even know what they have. So they'll give us what they say are their final surfaces and it will be something that was done in the 1950s. Assuming we can get a customer to give us their design surface, we could run a LiDAR model and show them what the `actual original' is compared to what they have. We've already done something similar at a small Mississippi airport in order to tell the state how much asphalt leveling they will be applying."

Risky Business
Risk management is another area in which both Burns and Smith see the IP-S2 playing a big role. Burns says that many of their projects, particularly those in an urban setting with sidewalks, driveways, etc., are easy targets for erroneous damage claims. To mitigate some of that risk, they've previously taken pictures of such locations in advance of project startups.

"To get such photos, though, I would have to make a field call, then determine what to shoot and how many pictures to take," he says. "Again, that's taking me or one of my crew away from more pressing business. And once done, we were left with just pictures."

By comparison, using the IP-S2, 360° hi-res images are captured along with the LiDAR data--images which can be georeferenced for easy viewing with Topcon's Spatial Factory or Orbit GT software. These "Street View" type applications allow a user to move through a project data set quickly, visually identifying potential risk areas and tagging them for review or cross-measurement with other items in the data set.

"This can virtually eliminate charges that something is not the way it was when a project started," he says. "The IP-S2 has a world of potential uses for us."

He adds that, while being one of the first in the region to have such technology can be daunting, it also underscores the commitment APAC has to using newer technology.

"We are fortunate to have management that understands what it takes to be competitive in this market and lets us move forward with things like this," he says. "We are bidding several jobs in the next few lettings and have already established which ones are going to be IP-S2-based jobs. Knowing we have this tool available allows us to aggressively bid on jobs like this one--jobs that can be both labor-intensive and time sensitive. It's a powerful advantage to have."

Larry Trojak is a communications writer for his own firm, Trojak Communications, in the town of Ham Lake, Minnesota. He is a frequent contributor to construction and survey magazines.

A 2.392Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

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