Setting out of Gridlines on Site

Setting out of Gridlines On Site

Today I wish to further discuss on setting out gridlines in a construction site.

Before and construction can be done, a set of construction drawings would be issued by the Consulting Architect firm. In these drawings the site layout plan and floor plans will be found. In these plans, there will be Grid Lines indicated with dimensions given. The grid lines allow references to be made in terms of position/location of various elements in the project. For example a partition wall position is determine in the floor plan by having dimensions indicated in the x and y axis, let say for an example - 2 meters from Gridline A, and 1 meter from Gridline 2

The Main Contractor will then engaged a license surveyor to set out the grid lines on site. The License surveyor will purchase a survey plan from the government land survey department indicating the true coordinate control points near the construction site and the license surveyor field team will for transfer and establish new control points if necessary and from these control points will go about setting out the grid lines in the construction site.

The license surveyor field team will normally set up the gridline reference points a few meters away from the building outline. When marking the gridline reference points they will as far as possible marked it on a permanent structure such as if there is a concrete pavement or a boundary wall or fence. If that is not possible they will drive a wooden peg/stake into the ground and marked the grid line reference point of the top of the wooden peg with a steel nail.

After the grid line setting out is done on site, they will bring their field data back to their office and have a drawing made out, showing the gridlines they have marked on site and the offset distances and other relevant information. When the gridline setting out drawing is ready, the license surveyor will endorse drawing and issue it to the main contractor.

Once the main contractor receives the drawing, he will give this drawing to his Site Engineer or the in-house surveyor if he has one. The Site Engineer or in-house surveyor has to then check and verify that the license surveyor markings on the drawing are similar to the markings on site. Prior to this, the Site Engineer or In-house surveyor has to protect all the marked points immediately after the license surveyor field team completed the marking of the gridline points. This is to avoid the gridline control points from being disturbed by other site activities.

If the site has a theodilite then the setting up of profile or batter board is not necessary. 

However, if there is no theodilite, then preparation of profile or batter board [see below figure 1 and 2 picture] for the transfer of the license surveyor grid lines to the top of the profile board is necessary. This activity is normally performed by the carpenters for the project. Profile or batter board is done so that the gridline point’s mark by the license surveyor field team is transferred up to a nail point on the profile board. The height of the profile board is normally 500mm to 1000mm above the formation level of the building. Normally the license surveyor points are either driven wooden pegs on the ground, or points driven by nails on a pavement or centre punch points on a brick wall. The purpose of a profile board is when there is no theodilite to give a line of sight for the gridline; the carpenters can tie a carpenter nylon string from one gridline point on the profile board to the corresponding gridline point at the other end of the site.

However, using profile board for setting out works is not encouraged for the following reasons:

1) Error in transferring from surveyors point to profile board.

2) When the profile board is disturbed

3) Inaccuracy in transferring from the carpenter string to the work element   

4) Different elevation on one end of profile board to the opposite end.

I realize my explanation may not be clear on gridline setting up, so I went to YouTube to search for some videos on site setting up and have attached it in this Post. However, the videos are also not very clear but it does give one a rough idea.

This end’s today Post. Have a nice day!