STABILITY PROBLEMS CAUSED BY SEAMS AND FAULTS

OFTEN THE EXISTENCE OF FAULTS OR SEAMS ARE KNOWN PRIOR TO EXCAVATION, HOWEVER, SOMETIMES THE BEHAVIOR OF THESE ZONES HAS BEEN MISCALCULATED. SOME OF THE APPROACHES THAT ARE AVAILABLE FOR CONSTRUCTING OPENINGS THROUGH FAULTS AND SEAMS ARE REVIEWED. BIERBAUMER (1913), I. STINI (1950), L.V. RABCEWICZ (1957), AND H. LAUFFER'S (1958) CLASSIFICATION SYSTEMS ARE BRIEFLY REVIEWED TO ILLUSTRATE THAT ALTHOUGH CLASSIFICATION SCHEMES HAVE OFTEN BEEN PROPOSED THEY HAVE NOT ALWAYS BEEN CAREFULLY USED. THE IMPORTANCE OF TERZAGHI'S (1956) SYSTEM, EITHER IN ITS ORIGINAL FORM OR WITH SOME MODIFICATIONS, HAS SERVED AS THE MAJOR FOCUS OF CLASSIFICATION SYSTEMS. DISCONTINUITIES IN ROCK MASSES ARE DISCUSSED IN SOME DETAIL. DISCONTINUITIES ARE FORMED THROUGH FAILURE IN EXTENSION/TENSION, IN SHEAR, OR IN MORE COMPLEX FAILURE THROUGH A COMBINATION OF BOTH. THREE CRITERIA ESSENTIAL IN ANY KIND OF CLASSIFICATION ARE: (1) SCALE, BASED ON APERTURE, PERSISTENCE, AND TYPICAL SPACING, IS BROKEN DOWN INTO 5 CLASSES - MICROFISSURES, BEDDING AND FOLIATION PARTINGS, JOINTS AND SEAMS, MINOR FAULTS, AND MAJOR FAULTS. (2) CHARACTER, BASED ON SMOOTHNESS AND THE PROPERTIES OF FILLING MATERIAL OR COATINGS IF ANY, IS DISCUSSED IN TERMS OF 7 GROUPS OR PROBLEM AREAS - JOINTS, SEAMS, AND SOMETIMES MINOR FAULTS; CLEAN DISCONTINUITIES (WITHOUT FILLINGS OR COATINGS); CALCITE FILLINGS; CHLORITE TALC, AND GRAPHITE COATINGS OR FILLINGS, INACTIVE CLAY MATERIAL; SWELLING CLAY; AND ALTERED MATERIAL TO A MORE SAND-LIKE MATERIAL. THE MAJOR TYPES OF DOMINANT MATERIAL THAT CAN BE FOUND IN GOUGE AND THE POTENTIAL BEHAVIOR OF THE GOUGE MATERIAL IS PRESENTED IN TABULAR FORM. (3) STRENGTH AND DEFORMABILITY, BASED ON MEASURED VALUES OBTAINED IN THE LABORATORY AND FIELD TESTING, IS DEVELOPED THROUGH THE CONCEPT OF JOINT ELEMENT. THE STABILITY PROBLEMS THAT FAULTS AND SEAMS MAY CAUSE UNDERGROUND ARE DEPENDENT ON: THE SIZE AND SHAPE OF THE OPENING; THE METHOD OF EXCAVATION; THE METHOD OF SUPPORT; THE ORIENTATION OF THE OPENING IN RELATION TO THE STRIKE AND DIP OF THE FAULT OR SEAM; THE WIDTH OF THE FAULT ZONE; ADJACENT SEAMS AND FAULTS, IF ANY; THE FREQUENCY, ORIENTATION AND CHARACTER OF ADJACENT JOINT SETS, THE COMPETENCE OF THE WALL ROCK TYPE; THE GAUGE MATERIAL; TIME ELAPSED AFTER EXCAVATION; THE IN-SITU STATE-OF-STRESS; AND THE WATER QUANTITIES.