# Development of an Automatic Rock Mass Classification System Using Digital Tunnel Face Mapping
## 1 Introduction  
At the design stage of tunnel construction, the quality of the rock mass along the designated route is classified based on geological survey results. Subsequently, suitable rock support patterns and reinforcement methods are determined according to the conditions of the rock masses observed at the tunnel face. However, discrepancies may arise during excavation if the actual quality of the rock masses deviates from the preliminary assessments conducted during the design phase. In such cases, it is essential to convene a rock quality evaluation committee. This committee is responsible for assessing the geological condition of the site and enacting subsequent amendments to the chosen support type or recommending additional reinforcement methods. This committee is tasked with performing an on-site evaluation of the excavation face by utilising an array of information, such as the results from tunnel face mapping, design documents, displacement monitoring data, and other pertinent data generated during the excavation process, which are provided by the field manager. However, such on-site rock mass evaluations are inherently time-consuming,as they necessitate the formation of a committee and a thorough assessment of the site's geological conditions, which invariably burdens the project team.  
Traditionally, tunnel face mapping has been manually conducted by geological specialists or geologists employed by construction firms. As shown in Figure 1, geological information on tunnel cross-sections is meticulously recorded, detailing the geometrical configurations and filling conditions of joint surfaces, the strength characteristics of the rock mass, and groundwater seepage conditions. This information is subsequently employed to assess various parameters related to rock mass quality based on typical classification systems in Table 1.  
In this context, the current study introduces the use of mobile devices, such as tablets, for capturing images of the tunnel face, and the acquired image data are used for digital mapping and rock quality rating [1]. Figure 2 illustrates the implementation of digital mapping through image-based data. The digital data generated during the mapping and rock mass rating are temporarily stored in the internal memory of the mobile device via a proprietary application, thus allowing offline functionality. When an Internet connection becomes available, the data are automatically uploaded to a centralised database. This innovative approach enables tunnel face mapping and rock mass classification in areas with limited or no cellular signal.  
Figure 1: Conventional tunnel face mapping using a geological sketch and RMR sheet.  
Figure 2: Digital mapping system using the tunnel face photo.  
Furthermore, geometric characteristics of the rock masses, including lithology and discontinuities, as well as groundwater information collected during the digital mapping process, are systematically stored in a database. This setup enables the rock masses to be automatically evaluated by cross-referencing the collected information with the rock mass rating table. Thus, the methodology significantly reduces the time and resources required for geological face mapping and subsequent evaluations while minimising potential errors associated with variability in the geologists' skill levels during mapping and evaluation tasks. This digital system enhances the overall reliability and efficiency of rock mass classification, ultimately contributing to improved decision making in tunnel construction management.