Construction surveys

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 locations for corners of the building have to be found by surveyor

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.

Establishing line

The process of giving line consists of establishing direction (angle)
and placing a series of marks along the line at determined distances. The angle may be set by theodolite. If a great accuracy is requested, then target wooden stake is re-measured by theodolite and from observed angle and distance, shift of the target is computed
Series of marks can be in need to find out positions for columns

Direction should be established from some backsight line, which is longer than line to be established.

Establishing grade

Marking elevations (also called giving grade, grade staking) is setting marks by tops of stakes or by nails on stakes.

The wooden stake is driven into the ground to mark requested elevation. Assuming the height of the instrument is known, elevation is set by means of level instrument.

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.

Many times it would be not convenient to drive the wooden stake so high to mark the requested level (42.27 on picture). Thus, wooden stake is driven into convenient height and is labeled by "fill". Fill tells how much to fill above the stake until requested height.
This is an analogy for fill. But in this case requested level is not above the stake, but below (at 46.94 on the picture). The stake is labeled by "cut" which tells how much land to cut until requested altitude is reached.

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.

Building stakeout

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.

Batter boards

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.

Batter boards made from wood are established around corners of planned building. They should be placed in a reasonable distance from construction. They serve together with line and grades. If line or grade is lost by the construction process, batter boards are helpful to re-establish them.
When the corners are being found by a surveyor, for good accuracy measurements should be taken rather from longer than shorter baseline.

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.

Column footings

Column footings

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.

Slope staking

It is common task—when road or railroad is being built—to align surface and the slope along the road (see picture below).

  1. Geodetic engineer is required to measure the terrain along proposed path.
  2. Based on observation by geodetic engineer the current situation can be used for preparing a project.
  3. Then geodetic surveyor shows by wooden stakes to contractor the point where to start filling the land or where to start cutting the land, according to the project:

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.

Slope staking illustration (cross-section at given kilometer):
A) F4.09/11.14: 4.09 m have to be filled (1.69 + 2.40), the stake is 11.14 m (6.14 + 5) from the centerline
B) F4.75/0: 4.75 m have to be filled, the stake is at the centerline
C) F5.85/13.78: 5.85 m have to be filled, the stake is 13.78 (5 + 8.78) from the centerline
The slope stakes are placed along the construction in intervals according to conditions, eg. every 10 metres.

Additional layout procedures

Prolonging a line (double centering)

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.

Double centering used to extend a line

Obstacle in a line

A property line between the marks might be obstructed or blocked by an object. The line needs to be found across the obstacle.

Line AD can not be established because of the obstacle.
1—(above) The method could be used only on low accuracy surveys; the larger is BC, the larger is error
2—(below) The preferred method: for best accuracy AB, CD and AA' have to be established as long as practical
3—(below) Fewer angles and distances than in the first method therefore better accuracy is achievable

Line and grade for sewer

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.

Manholes are openings which allow access to a pipe by a man. Manholes are placed for a purpose of cleaning and inspecting whenever the pipeline changes in slope, diameter or direction.

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.

The pipeline location is equipped with grade stakes and line stakes (in yellow color) along the path during construction. These serve as guides for excavating. When the ground is opened, then batter boards are installed to guide establishing the pipe into proper position.

Use of lasers

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.

1—Pipe laser, 2—Rotary laser

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