Layout of Foundation
Layout of foundation plan : After determining the width and depth of foundation, a drawing showing the width of foundations of various walls is prepared. It is known as foundation plan. To start the commencement of excavation, the centre line of one of the longest walls is just marked out by stretching a string between two wooden pegs, driven at the ends. Now set out the centre lines of other walls, The reference to this wall.
The centre line perpendicular to the reference line, is marked on the ground by 3 : 4 : 5 method. Suppose AB is the reference line. A line BC is to be marked as perpendicular to AB. Now set off a distance of 3 m (or three divisions of any length) on AB and take two strings of 4m and 5 m lengths, (or 4 and 5 divisions of the length taken on AB) and set out a triangle with these lengths as ides. The triangle HBG will be a right angled triangle and the line BC along BG will be perpendicular to AB.
After tracing the centre line of all the walls, masonry pillars or wooden pegs are driven at a distance of nearly 2 m from the centre line. The top of each of these masonry pillars or wooden page must be at the sea level, irrespective of the nature of the ground the height of these pillars is recorded with the help of a dumpy level.
The width of the foundations of each wall, is marked on either side of the centre lines and the work of excavation is commenced along the centre lines. With the help of masonry pillars the depth of foundation trenches, is measured. I the case of sloppy ground or undulations in the ground, these masonry pillars play a important role, as the actual depth of foundation trenches will not be equal but to avoid unequal settlement, the bottom of the trenches of walls having equal thickness or equal depth, must be at the same level.