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Roger Joiner, Survey Team Leader
When designing a construction site, surveying is an extremely important part of the process. It’s the first step that must be done in order for the engineer to know the existing topography, or geographical features of the land, which they’ll utilize when planning the design of a building or roadway.
In most cases, the engineer will develop a conceptual plan that’s practical for the site based on our survey. One important factor is to balance the cut and fill, or determine the amount of dirt that needs to be added or removed. This information minimizes the need to bring dirt in or haul it off the site. If dirt has to be hauled away from or onto the site it’s very costly.
Consider this example: You have a 40-acre building site where there’s going to be a big office building. If your elevations are off a consistent one tenth of a foot over the entire site, that equals out to 6,453 cubic yards of dirt. That’s a difference of about 240 dump truck loads of dirt, which is a significant amount.
Surveyors usually provide the engineer with a certified copy of the survey and in most cases a 3D computer-aided design (CAD) file where they can see the contours of the land and other features that affect their design. They can tell how steep the slopes are and where the ditches or drainage areas are located; these locations are very critical. Equipped with this information, the engineer is able to properly complete the design work.
When it comes to surveying and measuring vertical and horizontal distances, like most everything else, the technology has advanced. Laser scanning and UAV (Unmanned Aerial Vehicles) use some of the latest technology and are becoming very popular with surveyors. Almost all surveyors are now equipped with GPS (Global Positioning Systems). GPS isn’t quite as accurate as conventional methods, and it can’t be used on some projects, mostly wooded projects. We use both the GPS and the conventional surveying instrument depending on the location of the project and the accuracy required for that project.
If you need accurate elevations, the newest technology out there is digital leveling. With this technology, instead of a person looking through the level, reading a number and doing the math, there’s a bar code. The instrument reads the bar code and stores the information. It does all the reading and math for you, and you simply download the file. We have standards for accuracy involving elevations that we have to meet depending upon the project requirements.
The accuracy needed on the project depends on what type of survey you’re doing. For boundary surveys, or surveys that aim to formally establish the extent of a given parcel, the state has standards that surveyors must meet. The state gives you three standards of accuracy based on what type of property it is. If it’s in a rural setting where you’re out surveying someone’s farm or a timber company’s land for instance, the standards are not as great as if you were doing a survey in downtown Birmingham. Every state classifies them a little different, but they all basically follow that same rule.
As you can see, accuracy is extremely important when it comes to surveying, and there are an abundance of factors that can affect the measurements being exactly right. One mistake and you can throw off the design plans pretty quickly.
But no pressure, right?