How to Calculate Cut and Fill by Hand
Before building a house or undertaking any changes in a landscape, earth grading is required. Grading refers to shifting earth, or soil, through excavation and leveling to create an appropriate level surface for building, and enhance drainage. In some cases, like golf courses, grading is done to create small mounds and depressions other than getting a level surface. Site grading is usually done by cutting soil from high surfaces and filling lower ones.
This process is known as “cut and fill” grading. It is an important part of site preparation and sloping land away from a building site to provide adequate drainage. Before the process of earth removal (cutting) and placement on lower areas to raise them (filling) begins, precise calculations have to be made. These calculations determine the precise areas that will be excavated for cuts and how much soil is required for filing. It also helps determine soil quantities to be purchased when there is a shortage or driven out of the site when excess.
Today, technology has made the process easier for land grading contractors, landscape architects, and civil engineers. Using software like AutoCAD and ArchiCAD, volumes are calculated and cut and fill calculations done from the comfort of an office. Previously, the calculation of Cut and Fill by Hand was employed. This is through the cross-section or grid methods. For accurate results, top-notch precision and detail was required, which could take a day or two depending on the size of land.
The Cross Section Method:
The Cross-Section method requires a technician to draw horizontal lines across the site plan. These should be equidistant from one another. From here, the proposed and existing site elevations are plotted out on a graph paper, paying reference to the lines on the site plan. A comparison of the existing and proposed graph plots is then used to calculate the required cuts and fills. The cross-sections and volumes should determine how much soil should be imported and exported.
The Grid Method
The Grid Method involves drawing grids, which are vertical and horizontal lines creating boxes of equal sizes. For each corner of the grid cells, include the existing and proposed elevation then calculate the difference. This will show the required cut when the existing elevation is higher and required fill when the proposed is higher. The total amount of cuts and fills is then taken, and the average determined, after which further calculations can be made to determine the exact soil required for particular spots.
While most calculations are done by software today, calculating Cut and fill by hand remains a convenient method to obtain grading specifications!