Comparison of Earthwork Computation Methods

Modern technologies for data collection, data processing, and highway design allow for accurate representation of terrain-specific information to support volume computations for earthwork. These technologies support the representation of existing ground, design, and final as-built surfaces that can be overlaid and differenced to obtain volumes. However, most state highway agencies still use, or even specify, the average-end-area method, which relies on a coarse abstraction of cross sections. Results of an investigation of three highway design and construction data sets indicated, as expected, that when the cross-section interval was decreased, average-end-area volumes approached those computed by the surface-to-surface method. There could be exceptions, explainable by coincidence of the arbitrary cross-section interval and random variability of the terrain. Study results indicated that differences between the two methods could approach 5% when the cross-section interval was 100 ft. On one of the tested data sets, this difference in construction costs represented $112,500 for fill and $95,800 for cut.