## 4 Discussion and Conclusions  
The visualization and management of underground utility infrastructure are very important, considering the traditional techniques during the design, construction, and \begin{table}
\begin{tabular}{c c c} \hline \hline  & \
\begin{tabular}{c} **Traditional Underground** \\ **Utility Earthwork** \\ **Operations** \\ \end{tabular} &
\begin{tabular}{c} **BIM-GIS-Based Integrated** \\ **Framework** \\ \end{tabular} \\ \hline
2D visualization & Yes & Yes \\
3D visualization & No & Yes \\ Quantity takeoff & Manual & Automated \\ Material information & Basic & Detailed \\ Data sharing & Manual & Automated \\ Excavator operator visualization & No & Yes \\ Utility clash analysis & Manual (hard) & Automated (easy) \\ Design change & Manual & Automated \\ Facility management & No & Yes \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Qualitative evaluation of BIM-GIS-based underground utility management system. \begin{table}
\begin{tabular}{c c} \hline \hline  &
\begin{tabular}{c} **BIM-GIS-Based Integrated Framework** \\ **Qualitative Performance** \\ \end{tabular} \\ \hline Total utilities excavated & 47 \\ Utility strikes & 0 \\ Safety accidents & 0 \\ Utility clash identified & 7 \\ Rewrés & 2 \\ Additional utility identification & 5 \\ \hline Missed utility identification & 0 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Quantitative evaluation of BIM-GIS-based underground utility management system. maintenance stages. For example, the construction managers who use 2D drawings during the excavation face severe challenges such as utility strikes and lack of updated information system. Inefficient underground utility management causes direct damage to infrastructure, loss of life, and injuries, as well as a wider impact on the disruption of utility services to the consumers, project delays, and financial and legal consequences. 2D drawings are not capable of presenting enough information to facilitate construction managers in making effective decisions during the life cycle of the project. Furthermore, in the later stages, the information about existing utilities remains unknown because of a lack of inconsistent data records and a unified database. Therefore, an integrated framework is needed that is based on advanced technologies such as BIM and GIS. All the geometric and semantic information can be stored, managed, accessed, retrieved, and updated in a standard method at different project stages. This paper proposes an integrated BIM-GIS-based underground utility management, facilitating stakeholders throughout the life cycle of the projects. The proposed framework is composed of the following layers: (i) data source layer, (ii) data processing layer, (iii) integrated BIM-GIS platform, and (iv) application layer. The proposed framework is based on data collection using advanced surveying techniques for surface and subsurface information. The collected and processed data provide accurate information to develop a BIM model. BIM models were developed using the information from data source layer, which provides surface terrain model from UAV photographs, underground utility information through GPR survey, and other necessary information from local authorities such as 2D CAD drawings, reports, and attribute information. RTK GPS was integrated with UAV and GPR data to improve the accuracy of the model. The BIM model was integrated with GIS using IFC to CityGML mapping. The integrated BIM-GIS model contains all the necessary information such as geometric and semantic information required during different stages in the utility design and maintenance. The proposed BIM-GIS integration framework was successfully implemented on the real utility infrastructure project during the design, construction, and maintenance. The developed integrated BIM-GIS model facilitates the designers and construction managers to detect and prevent clashes between existing and new utilities during excavation design.