EARTHWORK COMPUTATIONS

Earthwork computations are the calculations of earthwork volumes or quantities to determine final grades, to balance cut and fill, and to PLAN the most economical movement of material.

Volume Changes

Most earthmoving is computed in cubic yards; however, on some project drawings, the metric system is used. A cubic yard is a cube 3 feet long, 3 feet wide, and 3 feet high. Many dimensions in field measurements and contract plans are in feet, so if they are multiplied together to obtain bulk (length x width x depth), the results are in cubic feet. To obtain cubic yards from cubic feet, divide the cubic feet by 27 (there are 27 cubic feet in one cubic yard). It is also possible to divide the original linear measurement by 3 to convert the numbers to into yards, and then multiply. However, this may lead to working in fractions, decimals, and mixed numbers.

Cubic yards of material are either in place, loose, or compacted. Material, excavated from its natural state, increases in volume, commonly known as swell. Undisturbed material is measured as in-place cubic yards, material loosen by handling is measured in loose cubic yards, and the volume of compacted material is measured as compacted cubic yards.

NOTE: When calculating estimates from project drawings, you estimate cuts as in-place cubic yards and estimate fills as compacted cubic yards.

To calculate the correct amount of material to be handled, you convert the present soil conditions by using table 15-1.

Road Nomenclature

A cross-sectional view of a road and its components is shown in figure 15-14. Before any construction is performed on a project site, the elevation is known as existing grade. The driving

Figure 15-14.-Road nomenclature.

surface of an existing road that is to be replaced is also known as the existing grade. The subgrade of a road is a prepared base for the placement of base-course materials. The base course is a select layer of well-compacted soil that is placed in compacted lifts on top of the subgrade. This compaction can be accomplished by mechanical stabilization or chemical stabilization. The surface course and the shoulders complete the road. The surface course is usually concrete or asphalt and is part of the road that vehicles travel on. The shoulder of the road performs as a retainer on each side of the surface course and provides an emergency parking area.

The crown of the road is an established slope from the center line of a roadbed to the outside of the shoulders and allows for excess water to drain from the surface into either a V type or flat bottom type of ditch. The area that covers the entire width of the road

Table 15-1.-Volume Changes

project, including the ditches, is known as the roadway. The roadbed is the section that includes the surface course and both shoulders, and the travel way is the surface course that the vehicle travels on.