# Voxel-Based Digital Twin Framework for Earthwork Construction
## 4 Implementation of the Proposed System
### Graphical Simulation Environment for Model-Equipment Interaction
#### 4.1.3 Model Integration in Platform
The results of the simulation cycle show that the proposed system provides an effective visualization of the earthwork operational process, where the equipment interacts and manipulates the as-planned model. Figure 10: Integrated models in Unity and a user interface for user interaction with the system. #### 4.1.7 System Evaluation

The volumetric changes in the simulation were compared with the volumetric changes at the actual construction site, along with the time taken by the equipment for the excavation activities. Volume accuracy was calculated by monitoring the voxel volume from the virtual environment and the earthwork material volume excavated from a real construction site. Accuracy was calculated from the volumetric differences between the virtual and actual environments using the following equation:

\[\text{Volume accuracy}\;(\%)=(1-\frac{|V_{simulated}-V_{real}|}{V_{real}})\times 100 \tag{10}\]

The earthwork volume at the actual construction site was calculated by scanning the excavation site and calculating the physical site volume. The proposed method uses

Figure 11: Excavation cycle activities. identically sized voxels and calculates the volume using the voxel size and the number of voxels. For a robust evaluation, three excavation volume measurements were taken, and the average of the three measurements was used for each material. The simulated vs. real volume data showed a close correspondence for each material (Figure 12). Gravel materials had higher accuracy because they consist of discrete particles and can accurately represent the contact forces and resistance between the model and equipment. The proposed method uses a larger voxel size, which creates an additional error between the simulated and real volumes. Smaller voxels can improve accuracy, particularly for silts, because of their fine material and characteristics; however, this significantly increases the computational cost. The proposed system balances accuracy and computational efficiency, providing more accurate results for granular materials. The time taken by each activity was similar between the virtual and real equipment (Figure 12b). The time taken by the dump truck to move from the excavation site to the dump site was the longest in the virtual earthwork cycle because the distance was long, and the movement was greatly affected by the ground topography. The results were similar to those of the real environment because the topography was developed using scanned data from the photogrammetry technique, which captures accurate as-built information. The proposed method uses a voxel-based representation that accurately captures earthwork information, utilizes Unity 3D physics, and makes the system suitable for large-scale operations. Beyond material properties and realistic models developed using data collected from real sites, several other factors contribute to the discrepancies observed between simulated and real excavation volume and time. One important cause is the simplification of equipment behavior in the virtual environment. In the simulation, equipment follows idealized, repeatable paths with fixed motion parameters, while in real-world operations, the skill level and behavior of human operators introduce variability in bucket angles, scooping depth, and dumping motions, which significantly affect the exact volume excavated during cycle time. Additionally, the model is simplified, and several key contributing factors, such as spillage, partial bucket loads, and soil sticking to equipment surfaces, are not explicitly modeled in the simulation. This simplification also causes over- or underestimation. Moreover, the system is implemented in Unity 3D, which does not account for the simulation of complex soil-tool interactions, such as deformation and breakage. These factors also impact realism. These simplifications, while needed for maintaining computational performance, collectively contribute to the observed differences and suggest areas for future enhancement using more advanced simulation techniques.