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|Yielding rock bolt systems have been developed to provide ground support while accommodating shifting, creeping, or swelling ground movements. The Dywidag Systems, Inc. (DSI) Slip Nut System is one such system. It has been tested in the laboratory and installed and monitored in the interbedded halite and anhydrite at the Waste Isolation Pilot Plant (WIPP) since 1994. The Slip Nut System is installed on a point anchored threaded bar or on a threaded bar coupled to a cable bolt. At a pre-engineered load the nut acts as a die and cuts through the thread on which it rests, thereby reducing the load and coming to rest on the next thread where the process repeats. Two types of laboratory tests were performed using slip nuts on DSI's threaded bars and their Tensionable Cable bolts. Straight pull tests exceeding 0.3m (1 ft.) of displacement were performed on the systems. Also, offset tests were performed on these bolt systems in a test frame designed to simulate WIPP geologic conditions. A room scale test area consisting of 186 threaded bars began in 1994. Select bolts were instrumented to track bolt load. All bolts were tracked through time for operation. Through three complete years since installation over twelve slips, corresponding to approximately 0.15m (6 in.) of ground movement, have been observed in some areas. Since installation strata offset has exceeded 0.08m (3 in.) at a supported clay layer in the roof. No bolt failures have been observed. Slip loads observed underground generally approximate those observed in the lab. To date, the slip nut systems tested and installed have performed as expected.|
Additional chapters/articles from the SME-ICGCM book 17th International Conference on Ground Control in Mining (ICGCM)
|Gateroad Pillar Extraction Experience at Jim Walter Resource||Stability of Backfilled Cross-panel Entries During Longwall||Mining Through In-panel Entries and Full-face Recovery Room||Cutable and Variable Yield Cement Cribbing Successfully Supp||International Experience with Longwall Mining into Pre-drive||Analysis of Geologic and Geotechnical Conditions and Their E||Comparison of Ground Conditions and Ground Control Practices||Application of Microseismic Monitoring to Longwall Geomechan||Control of Hard-to-Collapse Massive Roofs in Longwall Faces||A Study of Periodic Weighting of Longwall Supports||Effects of Panel Mining Sequence and Retreat Direction on th||Controlling Roof Beam Failures From High Horizontal Stresses||Roof Control Under Conditions of Shallow Depth and High Hori||Assessment of Roadway and Yielding-pillar Performance During||Practical Stress Modeling for Mine Planning||The Design of Room and Pillar Mining Systems in the UK||Geotechnical Planning and Development of the BHP Minerals Sa||Coal Pillar Life Prediction in the Vaal Basin, South Africa||An Analytical Approach to Determine Stress Distribution in L||In Situ Strength Testing of Rocks with the Borehole Penetrom||Performance and Safety Considerations of Hydraulic Support S||A Decade of Mobile Roof Support Application in the United St||A Critical Study of Strata Behaviour During Extraction of Pi||Progression of Longwall Gateroad Support as Conditions Chang||Application of the Coal Mine Roof Rating, Derived from Drill||The Effects of Reduced Annulus in Roof Bolting Performance||Laboratory and In Situ Results of a Slip Nut Yielding Rock B||Field Monitoring of Rock Bolting Performance in Weak Roof St||A Case Study of Bolt Performance in a Two-entry Gateroad||Automated Temporary Roof Support Systems: An Update||Safety and Productivity Innovations in Mechanized Bolting||Factors Influencing Intersection Stability in U.S. Coal Mine||Analysis of the Effect of Rate of Extraction on Strain Devel||Analysis of Panel Stability for Post-Mining Slurry Injection||Development of Timedependent Surface Subsidence Over the Tot||Transversely Elasto-Plastic Analysis of Surface Subsidence A||Landslide Occurrence and Causation in Steep Slope Areas of A||Rock Bursting and Seismicity During Ramp Development, Lucky||Advances in Remote Sensing Techniques for Monitoring Rock Fa|