2012-01-27_REPORT - M1973021 - Laserfiche WebLink

Home Browse Search

rock sloughing was observed and was classified as minor based on rock accumulations observed on bench surfaces throughout the Central Quarry. The general condition of the highwalls is anticipated to remain stable with only small scale rockfall expected to occur. The baseline rock conditions described in Amendment 3 to Mining Permit M- 1973 -021 are "competent" for granite or biotite gneiss and "poor" for shear zones or highly to extremely weathered zones that have the potential to decrease the stability of the slope. The conditions observed in highwalls mined in 2011 in the South Quarry indicate that the rock is predominately "competent" with a "poor" area located along the north highwall of bench 6700. Additional localized areas of "poor" rock were observed in the highwalls. Generally, the localized areas of "poor" are located near the end of highwalls or in areas of initial highwall development and several are anticipated to be "competent" once further rock is removed for processing. Over the majority of the quarry no features were observed that are anticipated to cause large block size failures. Markland (stereonet) orientation data indicates very low probability of wedge or toppling failures. Markland orientation data also indicates a low probability of plane failure; the plane failures are most probable on the foliation surface when it dips out of the highwall face at greater than approximately 38 degrees. The foliation orientation at several locations has the potential for plane failure. However, from observations in the field, any blocks loosened in this area will be limited in size and are anticipated to be caught on the bench below the highwall. These results are similar to previous geotechnical addendum data. Therefore, other projected failures are estimated to be limited to raveling of smaller blocks in localized areas. These localized failures are not anticipated to extend further than the bench width. Movement occurred during 2011 on the previously mined South Quarry bench at 6760 due to weak rock associated with the fault zone. The movement appears to have stopped and will be contained by the bench and road below. Future highwalls in this area will be designed and presented in a Technical Revision. 5.0 CONCLUSIONS 5.1 North Quarry The observed condition of the slopes within the North Quarry appears to be stable. Observations of the North Quarry include: • No large scale failures in the past year. • Minor accumulations of slough material and small rocks. • Nearly all material was contained on adjacent bench surfaces, however it is impossible to be entirely certain as water within the cell prevents full observation (observation of material on the cell floor). - 10- Morrison Quarry Annual Report 2011 P:\23514\ 133- 23514- 12002 \Deliverables \Dehv -01 - Annual Report \Annual_Report_2011 _Geotech doc January 2012