Before the start of the excavation work for the foundatin of a building the center line of the foundation of building must be marked on the ground as per the layout plan. This process is known as setting out or layout marking which involves driving the pads and constructing the pillars.
The center lines of other walls which are perpendicular to the long wall are then marked by setting out right angles. Right angle can be set out by forming a triangle with 3, 4 and 5 units long sides. The diagnal should be checked out ensuring right angles at all the corner.
The top of the pillar is plastered and it set at the same level preferbly at the plinth level of floor level of the building.
In this video you will see the marking for excavation being carried out at site. The center line of the longest outer wall of the building is marked on the ground by stretching a string between the pads embedded in the pillar. This line served as a reference line of marking the center line of all the other wall of the building.
Project the pads about the ground level and drive them to the distance of about 2 meters from the edge of excavation so that they are not disturbed. Stretch string joining the corresponding pads at the two ends of the line, the boundary of trench to be excavated can be marked on the ground with dry lime powder.