Surveying 2 Lecture Notes, Summaries of Analytical Geometry

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Surveying 2

By Dr. Khamis Naba Sayl

Figure 26.1 portrays a section of planned highway construction and illustrates some of the points just discussed. Centerline stakes are shown in place, with their stationing given in the English system of units. They mark locations where cross sections are taken, in this instance at full stations. End areas, based on the planned grade line, size of roadway, and selected embankment and excavation slopes, are superimposed at each station and are shown shaded. Areas of these shaded sections are determined, whereupon volumes are computed using formulas given in the next Section. Note in the figure that embankment, or fill, is planned from stations 10+00 through 11+21 a transition from fill to excavation, or cut, occurs from station11+21 to 11+64 and cut is required from stations11+64 to 13+00.

Type of cross sections

The types of cross sections commonly used on route surveys are shown in Figure 26.2. In flat terrain the level section (a) is suitable. The three-level section (b) is generally used where ordinary ground conditions prevail. Rough topography may require a five-level section (c), or more practically an irregular section (d). A transition section (e) and a side-hill section (f) occur when passing from cut to fill and on side-hill locations. In Figure 26.1, transition sections occur

at stations and while a side-hill section exists at 11+21 and 11+64, while a side – hill section exists at 11+40.

The width of base b, the finished roadway, is fixed by project requirements. As shown in Figure 26.1, it is usually wider in cuts than on fills to provide for drainage ditches. The side slope s [the horizontal dimension required for a unit vertical rise and illustrated in Figure 26.2(a)] depends on the type of soil encountered. Side slopes in fills usually are flatter than those in cuts where the soil remains in its natural state.

Cut slopes of 1:1 (1 horizontal to 1 vertical) and fill slopes of 1-1/2:1 might be satisfactory for ordinary loam soils, but 1-1/2:1 in excavation and 2:1 in embankment are common. Even flatter proportions may be required—one cut in other factors. Formulas for areas of sections are readily derived and listed with some of the sketches in Figure 26.2.