## 4 Results
### Data Acquisition Layer  
4.1.1. Collecting Pre-Established Information  
Two methods were applied for the 3D modeling of the Ochang utility tunnel. First of all, BIM-based 3D modeling was performed using as-built drawings of the Ochang utility tunnel at the time of completion for the entire section. The as-built drawings of the Ochang utility tunnel were categorized into two items and consisted of 423 CAD files for structures and facilities. These materials were well preserved as as-built drawings from the time of completion of the Ochang utility tunnel in 2001.  
Site-based 3D modeling was performed via laser scanning for the demonstration section; the details related to the procedure of data acquisition via LiDAR scanning are shown in Table 4. Drawings and LiDAR scans are needed during the LiDAR scanning process, in which designating and mapping reference points of surveying are important. Lastly, point cloud matching is required in which 3D scan data are connected according to the site and for each station.  
There are advantages and disadvantages of using as-built-drawing-based 3D modeling and LiDAR-based 3D modeling:  
The advantages of 2D-based 3D modeling are as follows:  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt}} \hline \hline
**Work Procedure** & **Major Details** \\ \hline Drawing printing & Check the work location on a numerical map \\  & Prepare for a site inspection and survey \\ \hline Site 3D scan & Site inspection and survey of facilities \\ Site & Site inspection facility properties \\ Site exploration and survey before project launch \\ \hline Select a survey position on the drawing & Select a survey position in CAD program according to the site inspection survey results \\ \hline Survey ground-level reference point & Survey a precise reference point on the ground connected to the utility tunnel \\ \hline Survey underground reference point & Link with the precise reference point surveyed on the ground \\ \hline Reference point data mapping & Mapping between 3D scan data and reference point survey data \\ \hline Point cloud matching & Connect 3D scan data to each station according to the site \\ \hline \hline \end{tabular}
\end{table}
Table 4: Data acquisition procedure via LiDAR scanning and major details.  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt}} \hline \hline  & **Main Features** & **Key Methodologies** \\ \hline Modeling layer & Infrastructure and sensor modeling & BIM: library creation and color code designation \\ \cline{2-3}  & Geospatial modeling & GIS \\ \cline{2-3}  & Information storage and linkage measures & Database and linkage \\ \hline  & \multirow{4}{*}{Abnormal situation management} & Fire detection \\ \cline{2-3}  & & Spatial object displacement \\ \cline{2-3}  & & Earthquake disaster \\ \cline{2-3} Service layer & & Flooding \\ \cline{2-3}  & & Space utilization \\ \cline{2-3}  & & Event prediction \\ \cline{2-3}  & & Asset management \\ \hline \hline \end{tabular}
\end{table}
Table 3: _Cont._Accessibility: 2D-based modeling is often easier and more accessible than LiDAR-based modeling as it can be created using basic software and traditional drawn tools.
* Cost-effective: 2D-based modeling can be less expensive than LiDAR-based modeling as it does not require specialized equipment such as LiDAR scanners.
* Simple: 2D-based modeling is simpler and easier to learn than LiDAR-based modeling, making it accessible to a wider range of users.  
The advantages of LiDAR-based 3D modeling are as follows:  
* High accuracy: LiDAR-based modeling can provide highly accurate 3D models of the underground utility tunnel, capturing details such as the precise location and geometry of objects and structures.
* High level of detail: LiDAR-based modeling can provide a high level of detail, including the position, size, and orientation of objects, which is important for simulating the operation and maintenance of the tunnel.