A section view of a proposed roadway is shown in Figure 1 with an existing grade point elevation of 100-ft. The proposed roadbed finish grade elevation at station 50+00 is 95.00-ft and slopes at 2% grade. The grade rod reading at station 55+00 is most nearly:
Solution:
The Height of Instrument elevation can be calculated:
HI = 100.00-ft + 8.5-ft = 108.5-ft
The grade rod reading at station 50+00 is calculated by:
HI - station 50+00 elevation = 108.50-ft - 95.00-ft = 13.50-ft
The distance between station 50+00 and 55+00 is 500-ft
The slope is set at 2%, therefore; 2% x 500-ft = 10-ft elevation difference between stations.
Add the results of the proposed roadbed slope which is 10-ft to the grade rod reading at station 50+00 to obtain the grade rod reading at station 55+00 which is 23.50-ft.