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Mainstreaming surveying, layout work

Mainstreaming surveying, layout work

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    National contractor Walsh Construction bought Trimble Tablets to go paperless while placing concrete for runway expansion at Chicago's O'Hare International Airport. Photos: Joe Nasvik

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    3D laser scanners. Able to shoot millions of points in every scan, the most expensive and technically sophisticated surveying tool. Imagine using a conventional total station or theodolite to lay out 10 or 15 points for a project. Now imagine setting up a 3D laser scanner, which looks very much like a robotic total station, and recording a million points in a few minutes. With this data, you can generate an infinite amount of information: locate any number of points needed, record information on a site to create CAD drawings, create as-built drawings, or generate accurate records of construction progress to use when job conflicts arise. Several large general contractors, as well as a few subcontractors, own these.

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    Once regarded as leading edge, robotic total stations are becoming increasingly common because unlike their predecessor — the total station — only one person is needed to plot points. An operator can stand at the instrument to shoot points and elevations for developing site information to help generate CAD drawings, saving time and obtaining information that might otherwise be dangerous to collect. These instruments also direct excavators and concrete placing equipment that require 3D contours. Total stations cost much less, but require two people to operate: one at the instrument and one at the rod.

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    Digital levels can be extremely accurate across long distances. They gather very precise elevations over long, level routes. Surveyors often use a rod with barcode lines that the level reads to determine elevation. Sometimes the rods used have barcodes instead of numbers, so the instrument reads the barcode to determine elevation.

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    Laser levels remain the construction industry's workhorse; just about every contractor uses them to set elevations or to guide equipment. Newer models automatically level themselves, are easier and faster to use, and are less expensive than earlier models.

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    Especially good for inside buildings or low-light conditions where the laser beam can easily be seen, small laser level systems establish level automatically and provide colored laser beams to help users lay out level, plumb, and square. Add a remote sensor to lock on the beam in bright light or outside conditions, and you also can easily plot points accurately up to about 100 feet. Inexpensive compared to other instruments, they're used for laying out floor tile, ceiling panels, or smaller forming applications.

By Joe Nasvik

In the past, surveying firms provided nearly all the layout work for projects. This began to change when equipment manufacturers recognized the potential of the contracting and public markets and began to design according to the needs of these potential consumers. Before that time, software for survey and layout instruments was difficult for anyone other than a licensed surveyor to understand.

Contractors continue buying into sophisticated surveying technologies, which gives public agencies more options when outsourcing survey and layout work. As equipment becomes more user-friendly, more contractors are able to offer these services. This, in turn, could translate into more and less-expensive alternatives for your department or agency.

One reason contractors were motivated to move in this direction was that surveyor firms had large work backlogs that resulted in job delays and lost contractor time. Today many construction companies have their own survey divisions to conduct their layout work.

The size of the company and the type of project have a lot to do with how a contractor deals with surveying, layout, and machine control.

Here are two examples.

Correcting plan errors

As one of the largest construction companies in the nation that self-performs concrete work, Chicago's Walsh Construction assigns teams to projects, such as the runway expansion at the Chicago Department of Aviation's O'Hare International Airport, to provide layout and surveying.

Andrew Stover, a survey manager for Walsh, says the company provides all the construction layout work for the project, which includes support to subcontractors. They also generate and maintain all the as-built drawing requirements of Walsh contracts. “In a job of this size, there are many plan errors, so a major responsibility for us is finding them and making corrections, and sometimes offering other solutions,” he says.

Walsh places all runway concrete with a string-less paver guided by three robotic total stations. The survey team provides the elevations and manages the movement and control of the stations for the paver. They also supervise and load CAD files into the survey equipment to control earthmoving equipment, which includes a 3D motor-grader controlled by a robotic total station.

Walsh believes in keeping up with the latest technology developments to maintain a competitive edge. The company's survey group, for example, bought Trimble Tablets , a handheld computer that incorporates a cellular modem, laptop, GPS, and controller, to go paperless on projects. All CAD drawings can be loaded into the instrument and updated in real time via the Web or by downloading information from a computer. Each tablet also provides direction to any Trimble surveying tool used.

Stover says the paper savings alone on a project this size can exceed $100,000 if the entire project is paperless. In addition to the tablet data collectors, Stover and his team use 3D laser scanners, robotic total stations, digital levels, GPS surveying instruments, and laser levels.