Elements of Railroad Surveying As with most building projects, surveying processes prove useful in two distinct aspects of rail design—initial construction and ongoing maintenance. Surveyors are employed to map out optimal rail routes and also work closely with engineers to determine what sort of grade, slope and curve to put where. A site survey is necessary before any drawings can be made, since one must understand the geographic restrictions at hand before hoping to surmount them. Once blueprints have been created the surveyor is again engaged, this time to ensure that the construction crew is accurately reproducing the design created by the engineering staff. Every element involved in a rail project requires the attention of a surveyor, from laying the track level and in the right place to proper location of platforms and stations, plus other infrastructure items such as signal poles, electrical wiring and drainage. Rail Line Complexities In an ideal setting, a rail line would run straight and true from start to finish, with no changes in grade. In that case, you would hardly need a surveyor at all. Since few circumstances permit this, though, there are certain parameters a railway surveyor must follow when laying out a rail route. First, any grade (climb in altitude) should be no steeper than two units high for every 100 units traveled. In other words, a train bed should climb no more than two meters in elevation for every 100 meters of track. When it comes to curves, anything more than 10 degrees is probably a bad idea, although you might be able to get away with a tighter turn if the curve is more steeply banked. Naturally, many of these measurements will depend upon factors the surveyor should know in advance. These would include such things as the track gauge (how far apart the rails sit from each other) and the maximum number of cars allowed (if such a restriction exists). Rail Track Geometry The railroad surveyor is mostly concerned about the track. While there are certainly other issues to consider—width and height of the road bed, right-of-way clearance above and on either side of the bed, and the proper placement of poles, mile markers and such—the transportation system will not operate properly if the rail itself is out of place. A number of devices are available to make sure that the geometry of the track stays true. High-speed scanning is one of the more recent innovations in this area. Employing laser imagery and customized software, the railroad surveyor can enjoy the scanning density of nearly half a million points per second. This process identifies the integrity of the rail material as well as its proper placement on the rail bed. The imagery created during the scanning process can be generated in 2D cross-sectional form. When combined with photo imagery, it can give surveyors and maintenance crews alike an accurate 3D picture of the rail’s condition. Bridges and Tunnels Perhaps the most challenging aspect of railway design involves the construction of bridges and tunnels along the right of way. Various aspects of engineering come into play when creating an optimal design for each. For bridges, the railway surveyor provides input on site selection as it concerns the geometry of the approach (cuts and embankments) and the track alignment along the bridge floor. During the construction phase, the surveyor is responsible to monitor continuously all aspects of the build-out. For tunnels, the railway surveyor’s pre-construction input is similar to that for bridges. During the digging phase, however, his participation is even more critical due to the necessity of locating the centerline above the site and then translating it to a viable straight-line bore through the rock while avoiding drift.
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Elements of Railroad Surveying
Land Surveys Pty Ltd are an engineering survey company who provide a complete range of building surveys in Perth & Karratha, Western Australia.
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