There are three different methods popularly used for doing Earthwork Calculation for Cutting/Filling Projects. Before discussing these in detail let us try to understand Some Basic definition of Terms related to Earthwork Calculation.
EarthworksEarthworks are engineering works created through the moving and/or processing of massive quantities of soil or unformed rock. Earthwork is done to reconfigure the topography of a site to achieve the design levels. Earthwork involves cutting and filling to achieve the required topography.
CuttingCutting is the process of excavating earth material from a work location to achieve the desired topography.
FillingFilling is the process of moving the excavated material or additional earth material to a work location to achieve the desired topography.
Let us take 2 Simple Examples for our Study
In the Example below the plot is 30 X 30 Meters and all the Grid levels measured at Grid level of 10M
Average method:In this method Levels at each grid point is found out. Difference between the Average of Two Sets of Levels multiplied by Area gives the Result. This is a very simple and straight forward method. But this can be used only when there is cutting or filling. When Leveling of surface includes both cutting and filling, Average method gives wrong result as cutting and filling values nullify each other while averaging.
Volume = Average * 900 = 0.606 * 900 = 545.62
Block Method (Division of Square Method):In this method, volume of cutting or filling is found out for each block and added together to get the final volume. This is mathematically simpler then Section Method, but more accurate than Average method. The problem of nullification is also encountered here when in the same block there is both cutting and filling. But here the margin of error is very small when compared to Average method for whole area.
Example 1(Only Cutting):
Volume = Sum * 100 (Area of Each block) = 5.455 * 100 = 545.5 (Cutting)
Note: Value 0.61 = Average (192.51, 193.71, 193.04, 193.14) – Average (191.9, 193.1, 192.43, 192.53) [Values taken from first 2 rows and 2 columns of ground and formation level)
Example 2 (Both Cutting and Filling) :
Volume = Sum * 100 (Area of Each block) = 4.6225 * 100 = 462.25 (Filling).
Note: Although in this example there is some cutting, because of nullification of value in same block we are not getting any value in Cutting.