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By S. Mehrdad Heidari

The concentrator plant is located near a very high (105m), large (- 500m) and steep (a, > 45' ) wall. Geologically, the wall was composed of very complicated formations and broad range of soils and rocks type in which a variety of local typical failures models have been occurred on different soil and rocks formations. The construction of concentrator plant structure and other activities have been overshadowed by these local failures. Safety and risk of huge failures were serious concern. For distinguishing the wall conditions a broad campaign of slope stability investigation with detailed geotechnical drilling on berms of wall have been done and the structure of slope was fully identified and further Lab tests and slope simulation models done. Slope stability of the wall was analyzed and the effects of instability factors were described in short term (for construction phase) and long term (for production phase).The results indicated, if a well-appointed drainage system is implemented, the overall stability of the wall in short term will not cause any particular problem but about long term stability, the wall must be supported by rock bolting, consolidation grouting, shotcrete reinforced with fibers. The results have been confirmed by passing one year after this investigation.

Jan 1, 2005

By Naj Aziz

n Australia, the common method of laboratory testing of bolt for load transfer capacity determination is by short encapsulation push testing. Some concerns are raised about the validity of the test methodology, as the method does not reflect on the actual load transfer characteristics of bolt in real field situation. Thus, laboratory testes were carried out to examine the load transfer mechanisms of bolts in both the push and pull conditions. Tests were conducted by shearing a short resin encapsulated bolt out of a cylindrical steel sleeve. Three types of bolts with different surface profile configurations were tested. The study was complemented with numerical simulation of the test methods. Irrespective of bolt type the average shear load and shear stress values were found to be greater in push test, and the displacement at peak shear load was greater in pull test. The average shear stifhess values were greater in push test. The numerical simulation of the bolts provided a clear understanding of the stresses and strains generated by different bolt profiles during both the pull and pull testing process, thus allowing a better appreciation of the load transfer mechanism process.

Jan 1, 2005

By John Magyar

Special foamed cements were used to stabilize and secure caving ground in a newly-reamed 12.5-ft diameter underground ventilation raise. Two zones of very poor Rock Mass Rating (RMR) material were encountered during reaming of a ventilation raise at Placer Dome's Turquoise Ridge Mime in Northern Nevada These zones caved to large cavities, continued failing, and could not be safely secured using standard rock bolting, wire mesh, and shotcrete procedures. In stable sections of the raise, the ground control plan called for the contractor to install 8-ft and 124 length resin grouted No. 7 Dywidag bolts, chain-link fence mesh and shotcrete. This work was conducted on three decks installed on the raise bore reamer. The first of the caved areas was approximately 1,500 cubic yards in volume and extended out to 40 ft beyond the wall of the raise. Placer Dome considered several options for structural fill to repair the area including pumped shotcrete, concrete, and placing and grouting aggregate. A safe, cost effective, and expedient method of stabilizing the raise with foaming grout and bolted liner plate was selected and successfully executed. The special fast-setting, foaming cement grouts used were Tekfoam and Tekseal® manufactured by Minova. The raise was quickly placed in service. Factors considered in selecting the foaming grout are discussed.

Jan 1, 2005