Unmanned aerial vehicle (UAV) is one of the most prominent technologies in the construction industry for data collection purposes. Compared with traditional methods, UAVs collect data faster and more efficiently at a lower cost. One of the construction works that can be monitored using UAV is earthwork. Earthwork monitoring is essential to complete the earthwork on time, according to plan, and within budget. This paper presents an application study on the UAV-based earthwork monitoring of a high-rise building project in the Republic of Korea. Earthwork of building projects have distinct characteristics. The area is excavated downwards to tens of meters deep, thus contractors deal with several types of soil. The building project is usually built in a densely built area. Therefore, contractors must monitor the slope as it poses landslide risk to surrounding areas. UAV can calculate the excavated volume, monitor the progress and the site, and document earthwork periodically and strategically. Based on case study, this study compared estimated volume based on GPS and actual excavated volume based on UAV survey and found 0.71% difference, indicating the reliability of surveying using UAV. However, the volume per soil type was quite different between both methods, resulting in 15.8% (USD 183,057) cost difference. This study shows that UAV technology is effective in monitoring the actual excavated volume, thus supporting fair business practices and transparency between stakeholders.

Risks are involved in every aspect of earthwork projects. This paper specifically discusses the cost risk associated with the volume calculation of such projects. In the design phase, it is not possible to accurately predict the quantity per soil type underground of the site. As a result, there are uncertainties in the excavation cost that may cause cost overrun. There is a need for an innovative method to forecast, control, monitor, and manage excavation cost from design phase to completion. There is, however, an innovative method for calculating volume accurately using a digital surface model method. The digital surface model can be acquired using GPS and unmanned aerial vehicles (UAV). This paper proposes a simulation model which is able to analyze, control, and monitor the cost based on excavation volume so stakeholders are able to gain the actual volume quickly and accurately. Monte Carlo simulation is applied to the excavation volume per soil type, resulting in a range of possible outcomes for excavation cost. The developed model was verified by applying it to an actual case project. Throughout the project, the cost was successfully monitored and maintained below the maximum expected cost. However, the final actual cost in the last simulation almost reached the maximum expected cost, indicating the need for cost monitoring. By periodically comparing the simulation result to the actual excavated volume obtained from the UAV, the proposed model can assist stakeholders in controlling the cost overrun risk and developing strategies during the earthwork life cycle.