PROTECTION AND REFERENCING
Most site operatives have little concept of the time, effort and expertise involved in establishing setting-out pegs. For this reason the pegs are frequently treated with disdain and casually destroyed in the construction process. A typical example of this is the centre-line pegs for route location which are the first to be destroyed when earth-moving commences.
It is important, therefore, that control stations and BMs should be protected in some way and site operatives, particularly earthwork personnel, impressed with the importance of maintaining this protection. Where destruction of the pegs is inevitable, then referencing procedures should be adopted to relocate their positions to the original accuracy of fixation.
Various configurations of reference pegs are used and the one thing that they have in common is that they must be set well outside the area of construction and have some form of protection, Acommonly-used method of referencing is from four pegs (A, B,C, D) established such that two strings stretched between them intersect to locate the required position . Distances AB, BC, CD, AD, AC, BD should all be measured as checks on the possible movement of the reference pegs, whilst distances from the reference pegs to the setting-out peg will afford a check on positioning. Ideally TP1 should be in line with DB and AC. Intersecting lines of sight from theodolites at, say, A and B may be used where ground conditions make string lining difficult.
Control point protection
Control point reference pegs
Although easy to construct, wooden pegs are easily damaged.Amore stable and precise control station mark that is easily constructed on site . A steel or brass plate with fine but deeply engraved lines crossing at right angles is set with Hilti nails into a cube of concrete cast into a freshly dug hole. To avoid any possible movement of the plate there should be a layer of epoxy resin between it and the concrete.