154 Beyond statistical injury rates, the reduction of high-risk interfaces represents a fundamental shift in operational safety logic. 2.2 Energy Intensity: Specific Energy Consumption Energy consumption during underground development is driven not only by rock fragmentation but also by ventilation demand, equipment operation, and auxiliary systems. Cyclic drill-and-blast excavation generates fluctuating energy profiles, including peak ventilation loads required for blast clearance and diesel particulate removal. A useful comparative indicator is specific energy consumption, defined as the energy input per unit of excavated length or volume (e.g., kWh per meter or MJ per cubic meter). This metric enables system-level comparison independent of total project size. Continuous, electrically powered excavation produces a more stable load profile and reduces dependence on diesel-powered equipment at the face. In addition, uniform tunnel geometries may lower long-term ventilation resistance, further influencing total energy demand over the development phase. Evaluating excavation technologies through the lens of specific energy consumption allows a more comprehensive understanding of operational efficiency and decarbonization potential. 3. STRUCTURAL COMPARISON OF CYCLIC AND CONTINUOUS EXCAVATION Excavation systems differ fundamentally in their process architecture. This structural distinction influences how risk, variability, and energy demand are distributed throughout the development phase. 3.1 Sequential versus Integrated Process Design Drill-and-blast development follows a strictly sequential workflow. Each cycle consists of discrete stages—drilling, charging, blasting, ventilation clearance, scaling, and support— performed one after another. Progress depends on the successful completion of each individual step before the next can begin. As a result, operational performance is governed by cycle efficiency and short-term execution quality. Cyclic excavation processes are generally associated with repeated personnel exposure at the face and discontinuous workflow patterns, which increase operational variability. Mechanized tunnelling, in contrast, integrates excavation, muck transport, and primary support into a coordinated system with largely parallel process components. Advance performance depends less on individual cycle events and more on sustained system stability.
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