SUPPORT DETERMINATIONS BASED ON GEOLOGIC PREDICTIONS

SINCE ROCK BEHAVIOR IS CONSIDERED TO BE THE KEY TO GROUND CONTROL, THIS PAPER PRESENTS THE FINDINGS AND CONCLUSIONS OF A STUDY ON THE METHODS FOR EVALUATING THE SPECIFICATIONS OF TEMPORARY ARTIFICIAL SUPPORTS BASED ON THE SEQUENCE OF MINING OPERATIONS AND PREDICTIONS OF VARIOUS ROCK CONDITIONS. FACTORS AFFECTING GROUND SUPPORT CONSIST OF: (1) GEOLOGIC FACTORS, WHICH ARE FURTHER SUBDIVIDED INTO: (A) ROCK TYPES, (B) JOINT PATTERNS, (C) DIP AND STRIKE, (D) DISCONTINUITIES, (E) FAULTS, SHEARS, AND FOLDS, (F) GROUNDWATER, (G) ROCK MATERIAL PROPERTIES, AND (H) WEATHERING OR ALTERATION; AND (2) CONSTRUCTION FACTORS, WHICH INCLUDE: (A) SIZE OF TUNNEL, (B) DIRECTION OF DRIVE, AND (C) METHOD OF EXCAVATION. IN ORDER TO DESCRIBE THE QUALITY OF A ROCK STRUCTURE ADEQUATELY, A ROCK STRUCTURE RATING (RSR) SYSTEM IS PROPOSED. AFTER A LITERATURE REVIEW WAS CONDUCTED A RIGID CONCEPT WAS DEVELOPED THAT STRESSED THE UTILIZATION OF 13 BASIC ROCK TYPES OF CONJUNCTION WITH 9 GEOLOGIC FACTORS: A MODIFIED VERSION RATES THE RELATIVE EFFECT ON GROUND SUPPORT REQUIREMENTS OF THREE PARAMETERS (IGNEOUS, SEDIMENTARY, AND METAMORPHIC ROCK TYPES) WITH RESPECT TO SEVERAL GEOLOGIC FACTORS AND WHERE APPLICABLE, TO EACH OTHER. TO CORRELATE RSR VALUES WITH ACTUAL SUPPORT INSTALLATIONS, IT WAS NECESSARY TO DEVELOP A METHOD FOR COMPARING DIFFERENT SUPPORTS ON A COMMON BASIS. THE CONCEPT, DESIGNATED AS THE RIB RATIO (RR), WAS DEVELOPED FROM TERZAGHI'S FORMULA OF DETERMINING ROOF LOADS FOR LOOSE SAND BELOW THE WATER TABLE. CHARTS, SHOWING THE RELATIONSHIP BETWEEN RSR VALUES AND CORRESPONDING RR VALUES, HAVE BEEN PREPARED. SUPPORT DETERMINATIONS SUCH AS STEEL RIB SUPPORT OR ROCK BOLTS AND SHOTCRETE ARE ALSO PRESENTED IN CHART FORM AS REQUIREMENTS THAT CAN BE CORRELATED WITH RESPECT TO GEOLOGIC PREDICTIONS AND TUNNEL SIZE.