Aid to survey-practice for reference in surveying, levelling, and setting-out; and in route-surveys of travellers by land and sea, with tables, illustrations, and records

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1880 Excerpt: ...driven in wooden bricks introduced for this purpose. Permanent level-marks in tunnels are spikes driven at the level of the skewback; there should also be a datum staple near the mouth and at the bottom of each shaft. At the adit entrances of tunnels the proper alignment for working is obtained by sights taken in the reverse direction; should a deep valley intervene and prevent convenient sighting, some mark may be set on the next rising ground or hill to serve the purpose of getting the direction at any time. The same method may also be adopted for fixing points over deep water, such as the extremities or corners of a jetty; two points in the correct alignment can be fixed on shore, and the position of the required point, when wanted for setting up staging or other purposes, is indicated by them, and also if need be by a cross alignment given by two other points. At sites of bridges, aqueducts, and such works, marks and stakes are liable to frequent removal during the progress of work; lateral marks are hence planted clear of the work in the alignment of the faces of abutments and piers or at any convenient distances, so that the positions of the corners of the abutments and piers maybe easily obtained from them at any time. In checking the points set out in this rectangular mode, the diagonals may be measured and compared; a hypothenuse-table is sometimes useful for these purposes. Side-widths of roads, railways, and canals.--These are set out on each side of every permanent stake at right angles to the centre-line. Cross-sections of the ground surface having been previously taken at these points and plotted to a natural scale, the central heights or depths of formation level are marked off on them, and a horizontal line drawn to represent the formation l...