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<br />Ms. Christina L. Komnikar <br />February 22, 2000 <br />Page 3 of 4 <br /> <br />Item #7 - A foundation for a home is typically designed azound the allowable bearing capacity of <br />the soil. For this region, the maximum allowable bearing capacity is in the range of 2500 psf to <br />3000 psf. Foundations for homes aze typically designed to stay within the bearing capacity range of <br />1500-2000 psf. The 3000 psf surcharge loading is a conservative estimate of any homes found in <br />this area. We have increased the stability model to show a 12000 psf loading (6 times the actual <br />amount). This increase in loading had no effect on the critical failure surface or on the <br />corresponding factor of safety against a failure. ~zµ' <br />•-- <br />Item #8 -The Division has never requested apseudo-static loading condition in the past. To the <br />best of my knowledge, there are no active faults in the azea of the mine site. The UBC defines the <br />azea as seismic zone one, which essentially means that the wind loading on a structure will exceed <br />any loading incurred by seismic activity. None of the homes or buildings in the area aze designed <br />for a seismic load, <br />The stability model has shown the critical failure surface for the gravel highwall. The dimensions <br />of this failure circle will not be increased by a seismic load. All of the setbacks are set so as to keep <br />the critical failure surface from impacting any of the surrounding structures. The only affect that a <br />seismic loading will have is to reduce the factor of safety against a failure. Irregardless of the <br />validity of analyzing a gravel highwal] in this area for a seismic load, We have added .OS horizontal <br />acceleration coefficient to the stability model. The resulting factors of safety were all above 1.0 and <br />~ ~' no increase in setbacks are warranted. If this is acceptable to the division, we will incorporate the <br />L -:,~ revised stability models into the final stability report. <br />.., <br />~.:. <br />Item #9 - A stability analysis for the unlined slope found in cells 1 and 5 is not warrwted. <br />Typically a stability analysis is conducted on the critical slope configuration. If the neaz vertical <br />/ highwall is stable during mining opetons (see Case lei) then a reclaimed slope of 3:1 in the <br />same location will also be stable. The unlined reclamation section uses essentially the same <br />material as the lined reclamation section. Please refer to Case 7 for any questions regazding the <br />stability of the unlined reclaimed slopes. <br />Item #10 -The effect of de-watering a site tends to lower the ground water elevations in and <br />,\,~ • azound the mine site. The phreatic surface shown in the stability model is the estimated (highly <br />~ ~ conservative) phreatic surface during the mining operation. <br />ciY <br />Item #ll -The stability model was performed using a near vertical highwall with a slope of <br />approximatelyp.lH to 1V. The mining cross-section shown on exhibit C will be revised. <br />Item #12 -The proposed conditions are acceptable. If it becomes necessary to increase the depth <br />of mining at the western and eastern boundaries of the site, the slope stability and proposed <br />setbacks will be reevaluated at that time. -~{- ~, <br />