Download - Engineering Surveyor

Offset pegsNeed for offset pegsOriginal setting-out lines (eg centre-lines) and setting-out points (eg the centre of a circular structure) are frequentlydestroyed, disturbed or obscured as the construction process moves forward. Installing offset pegs allows the originallines and points to be re-established.Work out where offset pegs will be needed in good time and install them as soon as possible.Offset distancesOn a slope, use a short offset distance to minimise any error in correcting for the slope. In general, keep all offsetdistances short, consistent with the pegs being reasonably secure against disturbance.All offset pegs should be located within the site boundary.Offsets points for sewer centre-lineTypically, replacement sewers are set out using steel pins to mark the centres of manholes. Additional setting-outpoints on the line are added as required. Offset pegs are then positioned perpendicular to the centre-line and locatedin an area least liable to disturbance from the trenching (or other construction) process. The distance from thecentre-line to the offset peg is measured; preferably, the offset distances should be kept the same. A simple methodof offsetting a right angle is adequate, eg with an optical square. Details of the original setting-out points, offset pegs,and offset distances should be recorded on a sewer information sheet.Offsets for roadThe centre-line pegs are set out first. In the diagram, offset pegs A and B are positioned beyond the edge of theearthworks but within the fence lines. The offset distances a and b may not be equal if the earthworks are notsymmetrical. Profiles for the earthworks can then be set out and/or re-established from these offset pegs.When the earthworks are complete, offset pegs C and D can be positioned clear of the outside line of the footwayusing offsets c and d from A and B respectively. Offset pegs C and D are used to set out the kerb line.Offset reference pegsFor a critical setting-out point, at least three offset pegs should be used in the event that one is disturbed ordestroyed.CIRIA C70933