Setting out of foundation trenches done by the following steps:
(1) First of all, the corners of the building are marked and then the lengths of the sides are checked by diagonal measurements.
(2) The axial lines (center lines) of the trenches are marked with the help of profiles, sighting rails, strings and pegs.
(3) The off-sets are measured from axial lines and the frontage lines are placed in their correct position relative to local requirements.
(4) The position of cross walls should be measured along the main walls and squared from these wails if desired, the total width of trenches being carefully outlined.
The following points should he observed while setting out trenches:
(i) Profiles, nails, strings and lime are used for Setting out the foundation plan.
(ii) Sight rails may be erected at the corners of a building to determine the correct position of trenches.
A theodolite may be used for marking accurately the axial lines ‘or’ center lines.
Strings are tied and stretched to the nails on profiles ‘or’ on pegs for horizontal control of dimensions.
(v) Vertical reference pillars are erected at a distance of 1 meter from the edges of excavation for vertical control of building during construction.
All the levels on site should be obtained from a fixed datum previously determined by the Surveyor. The depth of trenches and other levels should also be regulated by measurements from this point.
(vi) The bottom of all trenches should be well rammed before placing the concrete in position.