Prior to the construction activity the design information has to be moved from the plan to the ground. This is accomplished by staking. Slope stakes are an effective way to insure compliance with the design standards and to keep soil disturbance to an absolute minimum. Various staking methods can be employed. (Dietz et al., 1984; Pearce, 1960) The method discussed here is but one example.
Stakes, marking various road design points, are typically obliterated during the clearing and grubbing phase. In order to relocate the stakes (centerline, slope stakes) it is helpful to establish reference points outside the clearing limits. Reference points should be set at least 3 to 5 meters behind the uphill clearing limits. On the average, reference points (or RP's) should be set at least every 70 to 100 meters. Typically, reference points are placed at points where the center line alignment can be easily re-established, such as points of curvature. Figure 102 shows the necessary stakes and stake notation needed by the equipment operator to construct a road.
Stakes are used by the equipment operator in locating where to begin cutting. If the selected starting point is too high, considerably more material has to be cut in order to construct the proper subgrade (Figure 103). For example, if the cut results in a 20 percent wider subgrade, approximately 50 percent more volume has to be excavated. (See Section 3.2.2.) If the cut is placed too low, an overstepped cut slope or extra side casting may result, both of which are undesirable.
Starting the cut at the proper point becomes more important as the side slope increases. As a rule, slope stakes should be set when sideslopes exceed 40 to 45 percent depending on the sensitivity of the area and the operator's experience.
The use of RP's (Reference Points) or slope stakes for proper excavation is shown in Figure 104. Here, the engineer stands on the preliminary centerline of the construction grade and sights for the RP. A slope reading of 30 percent and a slope distance of 5.53 m is recorded. Converting the slope distance of 5.53 m to a horizontal distance of 5.30 m and to a vertical distance of 1.59 m allows the engineer to determine how much the "present" or preliminary centerline has to be shifted to conform with the design centerline. The RP tag requires 6.50 m horizontal distance to centerline with a vertical drop of 4.80 m. From that information, it can be seen that an additional 1.56 m [4.80 - (1.59 + 1.65) = 1.56] has to be cut and the present location has to be shifted by 1.2 m (6.50 - 5.30 = 1.20). Height of instrument or eye-level is assumed to be 1.65 m.
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