Once the volume has been calculated for each grid cell, all of the cut cells are added together to obtain the total cut volume. In either case, the volume is calculated by multiplying the cut or fill depth by the area of the grid cell. If the resultant depth is positive then this is a fill cell, while a negative value indicates a cut cell. The cut or fill depth for each cell is found by subtracting the average existing level of the cell from the average proposed level. By adding the volumes for each cell together the total cut and fill volumes for the project can be estimated. With these values the average depth of cut or fill required on each cell of the grid is calculated, and the volume for each cell is obtained by multiplying the depth by the cell area. The grid method involves drawing a uniform grid onto a plan of the earthworks project, and taking off the existing and proposed ground levels at each node of the grid. One of the disadvantages off the method is that it can be extremely laborious to extract cross sections from the drawing, and to determine the areas of the sections. These provide a useful visual summary of the estimation, which present the cut and fill depths across the project in a very clear way. One of the great advantages of this method is that cross sections are generated in the process. A balance has to be made between accuracy on the one hand, and speed of generating the estimate on the other. Closer sections improve the accuracy of the estimate, but take longer to estimate. The accuracy of the cross section method depends to a large degree on the distance you choose to set between the sections. This can save a great deal of time if you are using the cross section method. The spreadsheet included with this article includes formulae which have automated the process of calculating section areas using the trapezoidal rule. Other methods include drawing the sections in CAD and exporting areas or calculating areas mathematically using the trapezoidal rule. Multiplying the cell count by the area represented by each of the grid cells gives the cut or fill area for the section. Perhaps the simplest (but most time consuming) method is to plot the sections on gridded paper and count the grid cells of the cut and fill areas.
There are several different methods used to determine the areas of cut and fill, once the sections have been plotted. Once these volumes have been calculated for each pair of sections the total cut and fill volumes are obtained by adding them all together. The volume between each pair of sections is estimated by multiplying the average cut or fill area of the two sections by the distance between them.
For each of the cross sections, the cut area and the fill area is determined.
The cross section method involves plotting cross sections of the existing and proposed levels at regular intervals across the project site.
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