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Cut/Fill Calculations, Contour Method
Anytime you are shaping the ground, having cuts or fills is part of the process. Knowing how to calculate them will assist you when determining how much of each is required. There are several methods used to determine cut and fill calculations and each can be done using SketchUp. For this project, the contour method was used to determine cut and fill areas. First, the following groups must be copied and pasted into a new model space:
Determine the contour interval since you will need this as part of the calculations. When the property for the Weaver residence was surveyed, the elevation was unknown so an arbitrary elevation was set at 100 and one foot intervals were determined (Figure 1).
Figure 1. Cut/Fill - Elevations
Next, identify individual areas as cut or fill. To do this, identify the proposed contour and where it lies in relation to the existing contours. For example, contour 89 has a proposed change between 89 and 88, the proposed change occurs between contour 89 and 88, contour 89 would have to be filled. If contour 88 had a proposed change between 89 and 90, then contour 88 would have to be cut. This may be hard to visualize at first, but once you catch on, it becomes quite easy (Figure 2).
Figure 2. Cut/Fill – Identifying Cut or Fill Areas
To calculate individual areas bounded by existing and proposed contours for each contour, trace over the proposed area to create a face and create a group (Figures 3, 4, 5).
Figure 3. Cut/Fill – Tracing Around Contour for Square Footage
Figure 4. Cut/Fill – Closed Face for Fill
Figure 5. Cut/Fill – Finished Cut and Fill Areas
In ‘Entity Info’, select the appropriate layers for each group (cut or fill). Once all proposed areas have been grouped and layered, multiply area (square feet) by the contour interval to get cubic feet (Figures 6, 7). The square footage for each group can be obtained by:
Figure 6. Cut/Fill – Obtaining Area Information
Figure 7. Cut/Fill – Square Footage
Add all cut and fill volumes separately and divide each sum by 27 to get cubic yards. By calculating cut and fill volumes, you will be able to determine if you need fill hauled in or cut hauled away. If the two are equal, then it’s just a matter of moving the soil around the site.
For this project, the total amounts were:
Cut: 325.4798 SQFT = 12.05 CYD or 13 CYD
Fill: 1886.9235 SQFT = 69.88 CYD or 70 CYD
Divide each amount by 27 to get the total cubic yards. All totals can be rounded to the next whole number.
The volumes for this site were easy since the contour interval was one. However, if you have a site with a contour interval of five or ten, the volume calculator plug-in can be a useful tool for calculating cubic yards. The plug-in will calculate the volume for grouped forms (Figure 8).
Figure 8. Cut/Fill – Volume Calculator, Cubic Yards for Fill at 5’ Contour Interval
- Property Lines
- Existing Contours
- Proposed Contours
- Two additional layers are required: Cut (red) and Fill (blue)
Determine the contour interval since you will need this as part of the calculations. When the property for the Weaver residence was surveyed, the elevation was unknown so an arbitrary elevation was set at 100 and one foot intervals were determined (Figure 1).
Figure 1. Cut/Fill - Elevations
Next, identify individual areas as cut or fill. To do this, identify the proposed contour and where it lies in relation to the existing contours. For example, contour 89 has a proposed change between 89 and 88, the proposed change occurs between contour 89 and 88, contour 89 would have to be filled. If contour 88 had a proposed change between 89 and 90, then contour 88 would have to be cut. This may be hard to visualize at first, but once you catch on, it becomes quite easy (Figure 2).
Figure 2. Cut/Fill – Identifying Cut or Fill Areas
To calculate individual areas bounded by existing and proposed contours for each contour, trace over the proposed area to create a face and create a group (Figures 3, 4, 5).
Figure 3. Cut/Fill – Tracing Around Contour for Square Footage
Figure 4. Cut/Fill – Closed Face for Fill
Figure 5. Cut/Fill – Finished Cut and Fill Areas
In ‘Entity Info’, select the appropriate layers for each group (cut or fill). Once all proposed areas have been grouped and layered, multiply area (square feet) by the contour interval to get cubic feet (Figures 6, 7). The square footage for each group can be obtained by:
- double clicking to edit group
- selecting the face
- right click on face
- select ‘Area’
- ‘Selection’
Figure 6. Cut/Fill – Obtaining Area Information
Figure 7. Cut/Fill – Square Footage
Add all cut and fill volumes separately and divide each sum by 27 to get cubic yards. By calculating cut and fill volumes, you will be able to determine if you need fill hauled in or cut hauled away. If the two are equal, then it’s just a matter of moving the soil around the site.
For this project, the total amounts were:
Cut: 325.4798 SQFT = 12.05 CYD or 13 CYD
Fill: 1886.9235 SQFT = 69.88 CYD or 70 CYD
Divide each amount by 27 to get the total cubic yards. All totals can be rounded to the next whole number.
The volumes for this site were easy since the contour interval was one. However, if you have a site with a contour interval of five or ten, the volume calculator plug-in can be a useful tool for calculating cubic yards. The plug-in will calculate the volume for grouped forms (Figure 8).
Figure 8. Cut/Fill – Volume Calculator, Cubic Yards for Fill at 5’ Contour Interval
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