Earthwork - Area & Volume Calculation - Data Preparation
First step involved in doing an earthwork calculation is surveying the site. By surveying, the site elevations of the existing earth at various points of the work site are determined. Further, all the calculations are done depending upon these values.
Preparing for Earthwork Calculation:
From the point data available, a 3D Surface can be created with a software and then the volume can be found out directly from such surfaces using. However, it is expected that the volume we derive should be shown as a calculation and has to be printed for verification and for billing purposes.
So, we need to do the calculation in steps and first, we need to arrange the available survey data either in the grid level format or in the contour map depending upon the requirement.
- Finding the grid Levels [For section method, division by square method and average method]
Finding the grid Levels:
- Generating contour map [For Contour method]
For the first three methods, namely Section Method, Average method and Division by Square method, input elevations are converted into grid levels. It may be highly difficult to take the measurement exactly at the grid levels and hence levels are captured at various points of the work site as per the project requirement, and then those values are interpolated at the required points.
Interpolating the Available Elevations at the Grid Points:
Detailed explanation of interpolation is out of scope of this document and hence it is explained very briefly.
To find the grid levels from the available data, interpolation has to be adopted and there are different methods to find out the interpolation.
- Weighted average: Measure the distance from two nearest elevations and then find the weighted average to interpolate the value at the grid point.
- Triangulation: Triangulation is the process of connecting points to form a very large triangular network as per predefined algorithm (Delaunay triangulation theory being the most popular). Once the triangulation is done, then each triangle is considered as one surface and elevation at the grid point is calculated considering the point that, that particular grid point is on the 3-D surface where its x and y falls.
In the following example Grid point “A” is falling in the triangle marked by “P1”, “P2”, and “P3”.
In appendix section, we have explained how to find the elevation at a particular point with in a 3D Surface.
Grid levels thus found out become the basis of further calculation.
Volume Calculation (Earthwork / Takeoff) Methods Volume Calculation Methods