In this article, we’ll see how an estimator would use the cross-section method to calculate cut and fill for a construction site.
Before any construction can begin on a building site, it must be graded. In grading a building site, areas where the elevations are too high are “cut” or lowered down to the proposed elevations. Areas where the elevations are too low are “filled” or raised to the proposed elevations. Grading a building site requires a lot of time, equipment, staff and money. Accurately calculating the amount of work or cut and fill required to grade a site is necessary to prepare an accurate bid.
In the cross-section method, the estimator divides the site using a series of equally spaced horizontal cross-section lines that span the entire distance calculator drawing from east to east. He then plots both the existing and proposed elevations on graph paper for each of the horizontal cross-section lines. For each of the cross-sections, he then determines the cut areas and fill areas. Then for each pair of adjacent cross-sections he averages the cut areas and fill areas and multiplies them by the spacing of the cross-sections to determine the cut and fill volumes between the adjacent cross-sections. He then sums all of the cut volumes in all of the fill volumes to determine the total cut and fill volumes for the site.
Here the steps required to calculate cut and fill using the cross-section method:
Using a T-square, draw a series of equally spaced horizontal sections (ie cross-section) from East to West across the entire drawing. The spacing of the sections depends upon the complexity of the drawing. Drawing of high complexity should have their sections drawn one half-inch apart. Drawings of moderate complexity should have their sections drawn 1 inch apart. Drawings a low complexity should have their sections drawn between 1 and 2 inches apart.
Prepare a piece of graph paper for each horizontal section line. Draw a horizontal axis for the distance along the section from the left edge of the plan. Draw a vertical axis for the proposed and existing elevations using the lowest and highest elevation on the plan.
For each section, plot the existing elevations versus the distance from the left edge of the plan.
For each section, plot the proposed elevations versus the distance from the left edge of the plan.
For each section, calculate the number of squares where the existing is above the proposed surface. Then multiply the number of cut squares by the actual area of each grid square. This is the total cut area for this section.