When building roads, buildings, pipelines and other projects, it is a common task for surveying engineer to mark locations on the ground according to a project.
The marks placed are usually wooden stakes. These wooden stakes serve as reference points for either vertical or horizontal positions, or for both.
The line and grade must be established in a reasonable distance (1 to 3 m) from proposed construction prior contractor starts work. Craft persons (skilled workers) can draw positioning of constructions using rule and hand level then.
Direction should be established from some backsight line, which is longer than line to be established.
Marking elevations (also called giving grade, grade staking) is setting marks by tops of stakes or by nails on stakes.
To either push or cut the wooden stake to comply with requested altitude in given place according to a project is time consuming. Thus, other method is used: wooden stake is fixed to convenient level into ground. Requested height is compared with observed height. The difference is written with the stake as a cut or fill (letter C or F). That means the target height is below or above the top of the given stake.
The cut or fill is found by means of level instrument. Level instrument uses some known level to determine the height of the instrument and reading is made from rod placed on top of the wooden stake.
Very common complex task for surveyor is to reference corners and borders for construction of proposed building. For such purpose, a batter board is used as shown on the picture. Important part is a nail intended to hold string straight from one batter board to the opposite one. Because batter board is laid at offset of around 1.5 m from proposed building, the string can be temporarily taken off during construction while the board is still kept at the place to be used again.
The carpenters and masons can readily take a measurement from established strings by means of rule or plumb bob. Sometimes all the boards are set at a specific height to the ground floor.
The distances for proper locations of boards and strings is taken from baseline according to the project. Baseline might be the property line taken between monuments.
The column footings must be located with a high degree of accuracy (at most a few millimeters). Because footing is established in the fresh concrete before it hardens.
The elevation of base plates is critical also. Traditional differential levelling methods are used to set elevation of the plate. When the final position is established, cement is forced under the plate to fill the space.
The construction surveyor is also called on to ensure that the columns are placed in a truly vertical position. This can be achieved by using a plumb bob or by instrument.
It is common task—when road or railroad is being built—to align surface and the slope along the road (see picture below).
During the construction process, wooden stakes are pushed into the ground under an angle (slope). These are marked with the station number so the description of the height needed to fill/cut and stake distance from road centerline can be read also from protocol. The wooden stakes are established for every cross-section at distances of 10 or more metres.
It is often needed to extend given line. For example, line AB needs to be extended to C. So called double centering method is used to reduce the impact of instrument inaccuracy:
The point C1 is found by means of theodolite and marked. Then the telescope is reversed, and point C2 is found. If the instrument is in perfect adjustment, C1 and C2 will give the same result.
A property line between the marks might be obstructed or blocked by an object. The line needs to be found across the obstacle.
The slope is shown on the engineering drawing so that the builder can excavate the ground and place down the pipe in requested slope.
Whenever the pipeline changes in slope, diameter or direction, a manhole is build to provide access.
For construction, positions of grade stakes are established by surveyor. As the ground is excavated, its depth is being periodically checked by measurements from the grade stakes.
After the ground is open to a depth slightly deeper than that required, a series of batter boards is placed across the line at uniform intervals.
The batter boards are set at a constant elevation above the proposed pipe flow line, and a string line is run between the boards. String line is directly above the pipe centerline and has the same slope. It is then simple for workers to establish pipe into proper position making periodic measurements from the string line.
A straight beam is useful as a tool for giving a line and grade in construction surveying. The beam can be observed even under the sun and can be used outdoor. The laser instrument can be mounted on a tripod at a requested height: the laser beam is oriented in the horizontal direction and can serve as an electronic level.
The laser beam can be adjusted to a specific slope. That is useful for lying pipelines such as sewers, which require placing in slope of determined value according to the project.
A rotating laser beam is very useful construction survey tool. Instead of a single line it can generate flat reference surface over open area.