Escribe una PREreview

Thick and ultra-thick coal seams contain large resources; however, greater extraction heights amplify strata movement, coal wall instability, support demand, gas and fire hazards, dilution, and interruption risk. This review develops and foregrounds a conceptual six-gate, non-compensatory “study-to-assurance” framework that turns thick-seam method selection, demonstration, replication, and cross-mine transfer into an explicit evidence-to-decision pathway rather than a one-off design event. The framework specifies minimum evidence sets, auditable artifacts, and pass/conditional-hold/stop outcomes at six stages, from resource screening and geotechnical characterization to integrated design, instrumented demonstration, second-panel replication, and transfer to new blocks or mines. To support and bound this architecture, a structured critical review of literature and grey sources from 1950 to 2025 identified 300 records; 190 were screened, 145 full texts were assessed, and 120 sources were included across ten extraction or boundary option systems. Continuous miners have emerged as India’s most scalable mechanized underground system within a bounded cutting envelope, whereas high-reach single-pass longwalls deliver high outputs only within narrow geomechanical and operational windows. Although longwall top coal caving appears to address the residual height problem, it remains undeveloped in India. Historical blasting galleries, multislice, sublevel-caving, hydraulic, and descending-shield experiences are therefore not used as templates to revive but as engineering evidence that shapes the gate thresholds and failure tests. The proposed six-gate framework integrates evidence quality, geomechanical compatibility, coupled hazards, operational continuity, lifecycle economics, responsibility, and energy transition reporting. Its quantitative thresholds are demonstration minima, not statutory limits or design guarantees, and require field validation and mine-specific recalibration to be effective.