Challenges of Manual Rock Mass Classification in Tunneling

In tunneling and underground construction, understanding the ground is the first line of defense against uncertainty. The Rock Mass Rating (RMR) system has long been a cornerstone for assessing rock quality, guiding support design, and predicting excavation performance.However, when RMR is determined manually, engineers face significant challenges that can compromise both accuracy and efficiency. In complex tunneling environments, the reliability of design decisions depends on the precision and consistency of ground characterization — and manual methods often fall short.

1. Subjectivity and Inconsistent Results

Manual RMR assessment relies heavily on visual inspection and the personal experience of the engineer or geologist on site. Two professionals observing the same rock face may assign different ratings to parameters such as joint condition, spacing, or surface roughness.This subjectivity introduces inconsistencies that can propagate through design models, leading to variability in ground classification and tunnel support recommendations. Over time, these discrepancies reduce confidence in the data and complicate design verification.

2. Limited Coverage of Rock Conditions

Tunnels can extend for several kilometers, passing through highly variable geological formations. Yet manual data collection is often confined to specific stations or sections, constrained by time, safety, and access.This results in sparse datasets that may not capture rapid transitions in rock behavior — particularly in fractured or faulted zones. Without continuous data, design teams must interpolate conditions between logged points, introducing uncertainty in the ground model.

3. Time Pressure and Construction Constraints

Field teams operate under intense pressure to maintain excavation progress. Detailed RMR mapping takes time — time that is rarely available in fast-paced tunneling projects.As a result, geotechnical documentation is sometimes reduced to essential notes, with limited detail or photographic evidence. These gaps hinder later analysis and make it difficult to validate design assumptions against actual conditions encountered during excavation.

4. Data Fragmentation and Delayed Processing

Manual data is typically recorded on paper or in spreadsheets and then transferred to digital systems for reporting. This fragmented workflow can lead to delays, transcription errors, and information loss.Moreover, disconnected datasets prevent integration with monitoring results or numerical models. Without a unified digital workflow, the ground characterization process remains reactive rather than proactive.

5. Safety and Decision-Making Risks

In tunneling, conditions can change rapidly. If RMR data is slow to collect or process, decisions about support installation or excavation adjustments may lag behind the actual ground reality.This delay increases the risk of instability, overbreak, or water ingress. Reliable, near real-time understanding of rock mass conditions is crucial for maintaining both safety and project performance.

Conclusion

Manual rock mass classification has been the backbone of geotechnical practice for decades, but its limitations are increasingly evident in modern tunneling. Subjectivity, limited coverage, and data fragmentation reduce the reliability of design inputs at a time when precision and efficiency are more critical than ever. To meet the demands of today’s complex underground projects, the industry must move toward standardized, data-driven, and continuous ground characterization methods that deliver faster insights and more consistent results.