WORK RELATED TO PREPARATION OF PRESENTATION OF LAYOUT PLAN OF A BUILDING AND ITS MARKING ON GROUND
The operations carried out once the site is handed over
- Clearing the site
- Setting out the building
- Establishing a datum level
It is the process of developing the physical positions of corners and walls of a building, and it’s done by transferring dimensions from the layout plan (also called as setting out plan, demarcation plan) to the ground. The setting out clearly defines the outline of the excavations and the center line of the walls, so that the construction can be carried out according to the plan.
- Peg or rope method (commonly used).
- Dumpy Level (Best for big construction projects)
- Timber, 75mm by 50mm, or any appropriate size.
- Round poles/ timber to act as pegs or steel for hard ground.
- Nylon threads (Manila rope).
- Ordinary nails inch and 2 inches.
- White chalk or lime.
- Clear hose pipe for determining horizontal levels.
- Sledge hammer
- Measuring tape
- Builder’s square
A point which serves as a reference or base for the measurement of other quantities where there are no benchmarks on or near the site, a suitable datum must be established. A site datum or temporary benchmark could be a post set in concrete or a concrete plinth set up on site.
- Setting out is done on the principle of whole to part. According to this principle the largest possible rectangle of the building is found and set out. The rectangle is further partitioned into small parts (internal rooms).
- The first thing we need to establish is a parallel/ reference/ base line, to which all other lines can be related. This can be taken along an existing building close to the proposed new structure/ boundary wall if existing/ kerb line etc.
Two square offset lines are set from the kerb to the position of the building line. The length of the line is greater than the width of the proposed building. Pegs are positioned at these points and a ranging line is fixed to these, giving a position of the building line.
After taking the dimensions from the drawing, the frontage line is set out. This can be either on building line or behind it. The first corner peg (A) will be positioned from dimensions given on the drawing which relates to site features such as distance from kerb, gate post, boundary wall etc. E.g. The point A is positioned a distance of (D) from the boundary Following the position of first peg, the second peg (B) is positioned after carefully measuring the width along the frontage line. The nail is knocked into each peg to determine the exact position of the corner.
Attach the taut line to the nail on the corner peg which will be extended well beyond the length of the wall to be set out Adjust the line carefully to cross the frontage line at 90 degree by using a builder’s square or the 3:4:5 method. When the line is correct, knock the peg with nail at the distance greater than the length of the wall.
One of the most important procedure used in setting out is the process of ensuring that all right-angle corners are properly aligned. One of the simplest ways is to use the method known as 3:4:5 triangle method.
- A peg with a nail is fixed exactly at 3m from the corner peg on the fixed line.
- A measuring tape is the hooked to the nail on the corner peg and another tape is hooked to the nail of the peg on the front line.
- Both the tapes are pulled towards the end wall and with distance of 4m showing on one tape and 5m on the other tape. Where they cross third peg will be fixed.
- This will establish a line at 90 degree to the front line.
Measure the same length from the frontage line and set point D.
Check the ranging lines before proceeding.
Measure the dimensions of the building side wall from the outer peg of the frontage line and set pegs parallel to the wall lines. Attach ranging lines to the pegs to establish the back wall line.
Pegs can be positioned at G and H, but this is not essential.
The setting out will be confirmed if all measurements are correct and the diagonals measure exactly the same. Measure the dimensions from A to G and B to H. these should be same if the building has been set perfectly. If there is some difference in the measurement, adjust the back pegs as per dimensions. The frontage line should not be altered.
When the building has been set out and proved by checking the diagonals, profiles can be erected to enable the corner points to be easily located after the trenches have been excavated. The ranging lines attached to the pegs are extended by holding the line to pass over the peg to the profile. The wall position is then clearly marked on the profile.
The profiles are positioned well away from the proposed excavations to allow an adequate working space. This is even more important when the excavations are to be carried out by a mechanical means.
While setting up profiles, it is essential that they are as level as possible. This avoids inaccuracies when re measuring the walls and diagonals before commencing work. The profile is most conveniently levelled to the DPC level of the proposed building.
A boning rod is a simple device used to quickly position levelling pegs. It consist of two pieces of timber nailed together at right angles. Boing rod can be used to transfer levels between the two known points.
Before excavation begins, the position of the foundation trench is marked on the ground. The original corner pegs can be then removed. The foundation line is then marked using lime or spray paint.
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