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i • • <br />' ~ STEEPEN ROBERTSON AND KIRSTEN <br />' Alana $COtt <br />September 16, 1994 <br />i Page 4 <br />Excavation operations should be closely observed in an attempt to discern the depth of crack propagation. <br />In addition to backhoe trenching, this may involve careful hand excavation and detailed observation. <br />Documentation of the depth of cracking may provide additional indication as to the nature of its origin <br />and ensure complete repair of the feature. Observation of the excavazion activities will be critical to <br />verify which type of event occurred, i.e., localized settlement or sloughing. <br />Blvlitl has indicated that it will undertake repair of the erosion along the liner cover, the upstream <br />embankment face and the downstream embanl®em groin areas, including sediment removal from the <br />solution collection ditch. Regrading of the north access road should help alleviate &ture liner cover <br />erosion problems. The proposed regrading of the dam crest, combined with the drainage troughs az either <br />' abutment, should alleviate future erosion problems at the upstream embanlmtent face. The exposed liner <br />area outside the downstream toe of the embanlQnent should be anchored to secure its position. Aachoring <br />' with a relative]y coarse material would serve this purpose. At the same time removal or stabilisation of <br />the erodible soils on the abutments, adjacent to the downstream embankment face, would) reduce sediment <br />generation potential. <br />The south diversion ditch appears to be functioning u designed. However, it may be desirable to remove <br />' the sediment which has accumulated neaz the culvert inlet, to the extent practical, to avoid remobilizing <br />this sediment during future storm events. <br />The option of leaving the Phase 2, Raise 1 fill as it is with the crack feature is sot recommended. If <br />excavation of the cracked fill indicates a slope failure, a slope stability analysis must be completed to <br />' evaluate ramifications for Raise 2. The previous desigrt analyses do not model the e~tisting, cracked <br />condition. Buttressing the area with tailings will enhance the stability, but may not malt the necessary <br />design requirements of seismic loading just after placement of the Raise 2 fill and little or no additional <br />1 tailings buttressing. Therefore, if a slope failure has occurred, the available optioaci involve either <br />reconstructing the fill in the cracked area or conducting a stability analysis to determine if the <br />I reconstruction is necessary. if only a localized settiemeat has occurred within the crest Area, minor fill <br />repair is considered sufficient to correct the situation. <br />I /rf <br />I Attachment <br />