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

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V. GEOTECHNICAL DATA ANALYSIS 5.1 General Specific slope stability analyses were conducted for the failure area investigation and repair in the East Highwall of the Central Quarry. General reviews in other areas were conducted to check that observed conditions were consistent with the conditions assumed during earlier design and used as the basis of the Observational Method discussed previously herein. ' Two rock mass conditions were previously analyzed during design, and used as the baseline for further evaluations. "Competent rock", representing the majority of expected conditions, and "poor rock" representing localized areas of shearing, weathering or adverse jointing were the two baseline conditions. Typical in-situ rock mass characteristics for each of these baseline conditions and the corresponding strength envelopes and calculated safety factors were presented in Permit Amendment No. 3, Section 4-04. Following are descriptions of general ground conditions observed relative to the baseline conditions for each of the areas worked during 1996. A summary of specific geotechnical analyses performed for the successful repair of the slide area in the East Highwall of the Central Quarry is also provided. 5.2 East Highwall of the Central Quarry ' A. General ■ The highwalls and benches are aligned at approximately N300W. ■ The rock material within the weathered zone is weak and is estimated to have an unconfined compressive strength less than 15,000 psi. The weathered zone typically extends from the ground surface to depths of 10 to 50 ft, and locally can extend deeper to approximately 60 to 70 ft. ' ■ The rock material below the weathered zone is typically stronger and is estimated to have an unconfined strength of at least 15,000 psi although localized zones of weaker rock are present. ■ The primary joint set is along foliation of the gneiss and schist rock ' the strike of which varies significantly, but is generally sub-parallel with the slope. The primary joint set typically dips 20 to 60 degrees in a westerly direction, sub-perpendicular to the slope. Data collected in 1996 revealed a greater number of occurrences of foliation dip at angles shallower than the slope angle of approximately 35 degrees than were observed in 1995. The strike also varied more from the ' orientation generally sub-parallel to the slope. Folding and shearing has created a series of small E-W to ENE-WSW trending synclines ' 8 G:\PROJECrS\20200\002\96ANNRPr.WPD