Back to Basics
Sometimes working alone is by choice and other times it is due to someone not showing up for work. How is it possible for only one person to perform measurement and layout? With the advent of robotic total stations and GPS, one-person surveying is much easier to accomplish and is becoming a common practice. However, if these rather expensive technologies are not available to you, how can lines be measured? How can elevations be determined? How can alignment be given? Although it isn’t as easy as when two people are available, surveyors working alone on a project do complete all of these activities, and many more, every day.
I relate working alone in surveying to working alone as a woodworker. An efficient woodworker figures out what is needed when building a jig to do a repetitive task. The jig then acts as a second person in the activity. A surveyor has to figure out how to create jigs in the field to act as second people. An example might be to use a shovel with a “D” handle to hold up a level rod as readings are taken. Another might be to use a bungee cord around a tripod to hold a level rod vertically over a bench mark. Yet another surveying jig might be to use some stick-on targets and to stick one to a 2 x 4 that can be placed over a line for a backsight.
There are other techniques in layout that are used when working alone. Remember, sometimes the needed measurement will require a lot of planning and creativity, but where there’s a will, there’s a way.
Establishing a BacksightObtaining a backsight by yourself requires some planning and a little extra effort when setting a point. But it is a simple task that should be used all of the time.
On a hubWhen setting a point, take the time to drive a nail directly on line behind the cupped tack that marks the point. (See Figure 1.) This nail can then be used to sight on (if there aren’t any obstacles in the way) from an instrument set up on the same line. To make the nail more visible, put a piece of surveying ribbon on it. If the hub is behind grass or dirt, consider hanging a plumb bob from a stake or stick.
On a wallOften, when setting a point on a line, there are buildings directly behind the point where a small target could be placed. Of course, you should ask for permission to place a target and explain that it is temporary and will be removed after the project is complete. Generally, a small plastic target can be glued to the wall and will not leave any noticeable marks when removed.
The owner of a building may refuse to give you permission to place a target. In this case, while your instrument is sighting on the point, move your line of sight to the building. Look for any distinguishable mark on the building you can come back to anytime you need a backsight on the line you are setting. Possibly the line of sight will hit a crack in the wall just above a window or hit the edge of a joint, or something similar that can be described in your field book and used by anyone using the line.
Establishing a LineMarking a line cannot easily be accomplished alone because you need to be two places at the same time. However, there is a method that can be used to mark the centerline for a column form on a concrete slab.
After an instrument has been set up and a backsight has been taken on the nail or target described above, turn the angle required for the layout and sight to where the line is required. Since you are operating alone, no one is there to mark the point. You will have to walk there yourself to mark it. Take a level rod or something else you may have with graduations on it. Knowing about where the line of sight is, lay the rod down facing the instrument. (See Figure 2.) Go back to the instrument and read the rod with the vertical crosshair carefully. Return to the rod and mark that reading on the surface. That mark represents the point you wanted to establish.
This procedure can be expanded to set points on both sides of a column so a straight edge can be used to establish the centerline of the column. Furthermore, the instrument can be moved to a control line 90 degrees away to establish the centerline of the column in the other direction using the same procedure. This method of using a rod or something similar that is graduated can be used time and again to establish line when working alone.
Obtaining an H.I.
(Height of Instrument) Obtaining an H.I. to begin leveling requires some preliminary work. When a bench mark is established, it must be located near something that is vertical such as a power pole, a building, etc. Locate a place to attach the face of a rod onto the object. (See Figure 3.) Now, whenever you need an H.I., set up the instrument so the face of the rod can be seen, read the rod and add the reading to the even-foot elevation. Now you have an H.I. for the work you are ready to do.
Checking GradeHow can you stand at the instrument and hold the rod at the same time to do one-person grade checking? It isn’t always easy, but one-person grade checking can be done.
An old spare tripod might be used as a support for the level rod. Modify it so the rod can be held in place while you walk back to the instrument to take a reading. (See Figure 4.) Large rubber bands can be stretched to hold the rod firmly. Or a C-clamp can be used to hold the rod to the tripod. Equipment suppliers sell a device for just this activity. If you have an old level rod that is still usable, consider attaching 1" x 2"s to it with screws to serve as tripod legs.