1997-07-28_GENERAL DOCUMENTS - M1973021 (9)

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' IV. GEOTECHNICAL DATA COLLECTION SUMMARY 4.1 General ' During 1996, additional detailed geotechnical data was collected for the localized failure area in the East Highwall of the Central Quarry. General observations were made in the other active mining areas elsewhere in the Central Quarry and in the North Quarry, but no detailed data collection was performed for interim slopes there. The additional detailed data collected for the failure investigation and repair in the Central Quarry consisted of geologic mapping, drilling five core borings, performing ' geotechnical laboratory testing on rock core and clay gouge (probable slide plane) samples, installing a temporary inclinometer in one of the core borings, and optical survey of surface survey monitor points in and around the failure area. ' During 1996, outside of the small failure investigation area on the East Highwall of the Central Quarry, excavation in the Central and the North Quarries did not exceed ' any conditions which would require reevaluation of stability of the cut slopes. New slope stability evaluations were performed only for the failure area to affect remedial design and repair. Other work in the Central Quarry was limited to excavation of ' benches at least 40 ft wide and highwalls 40 ft high at the south end, and to the planned bench configuration(50 to 60 ft wide benches and 40 ft high highwalls), or flatter, on the east side. ' Within the North Quarry, the 1996 highwalls and benches did not exceed an overall slope configuration of 1H:1V. CAMAS and Haley &Aldrich have continued ' periodic observations of the temporary slopes in this area although evaluations and reporting of slope stability and geotechnical data for temporary slopes of this configuration are not specifically required by conditions of the approved permit ' amendments. 4.2 East Highwall of the Central Quarry A. Geologic Mapping Geologic mapping was conducted in the vicinity of the one area of instability ' encountered during active mining during 1996 by Haley & Aldrich. Mapping activities included inspecting slopes from a distance to try to identify large- scale features and structures and to determine trends not evident at a closer ' range. Mapping documentation focused on identifying and recording conditions and individual features of each highwall. Included in the mapping was identification, measurement, and documentation of the quality and ' strength of the parent rock material; the strike and dip of persistent joint sets; joint frequency; and joint conditions as exposed in the highwalls. ' Results of the geologic mapping for this part of the East Highwall are presented in Appendix A as a plan map of topography for the upper East ' 5 G:\PROIECfS\20200\002\96ANNRPT.WPD MM