212 EARTHWORK 



3. The line between columns 3 and 4 may then represent 

 the center line; the intermediate points between the left-hand 

 slope stake and the center are given in their order in column 3. 

 Similarly, the points on the right side are placed in column 4. 

 The figures for the right-hand slope stake are always placed 

 at the extreme right-hand side of that column. 



The preceding table shows how the computations are 

 arranged. Take, for example, the section between Sta. 128 

 +40 and Sta. 129. To find the end area at Sta. 128+40, 

 the following fractions are written: 



4\/ 0_ 

 12.0/ \46.2/\31.0/ \19.5/ /\13.7/27.6xJ\I2.0 



The products of the numbers connected by full lines, 12.0 

 X22.8, 46.2X20.4, etc., are written in column 2, and the 

 products of those connected by dotted lines, 22.8X31.0, 

 20.4X19.5, etc., are written in column 3. The sum of the 

 double plus areas is 2,696.6, and the sum of the double minus 

 areas is 1,247.1. The area of the section is, therefore, iX 

 (2,696.6- 1,247.1) = 724.8 sq. ft. 



The area at Sta. 129 is obtained in a similar manner; thus, 

 i (1,144.8 -407.7) = 368.6 sq. ft. 



The volume for a 100-ft. section as figured by the average 

 end-area method is 



For Sta. 128+40, 



And for Sta. 129, 



X368.6-683cu.yd. 



These figures are entered in column 4 (a) of the table of 

 computations. 



If the prismoid were 100 ft. long, the volume V a would 

 be 683+1,342 = 2,025 cu. yd. As the prismoid is but 60 ft. 



