Improving Accuracy in Earthwork Volume Estimation for Proposed Forest Roads Using a High-Resolution Digital Elevation Model

Earthwork usually represents the largest cost component in the construction of low-volume forest roads. Accurate estimates of earthwork volume are essential to forecast construction costs and improve the financial control of road construction operations. Traditionally, earthwork volumes are estimated using methods that consider ground data obtained from survey stations along road grade lines. However, these methods may not provide accurate estimates when terrain variations between survey stations are ignored. In this study, we developed a computerized model to accurately estimate earthwork volumes for the proposed forest roads by using a high-resolution digital elevation model (DEM). We applied our model to three hypothetical forest road layouts with different ground slopes and terrain ruggedness conditions. We examined the effects of various cross-section spacings on the accuracy of earthwork volume estimation assuming that 1-meter spacing provides the true earthwork volume. We also compared our model results with those obtained from the traditional end-area method. The results indicate that as cross-section spacing increases the accuracy of earthwork volume estimation decreases due to lack of the ability to capture terrain variations. We quantified earthwork differences, which increased with terrain ruggedness ranging from 2 to 21%. As expected, short cross-section spacing should be applied to improve accuracy in earthwork volume estimation when roads are planned and located on hilly and rugged terrain.