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CHAPTER VI <br />DESIGN CRITERIA 6 CALCULATIONS <br />SUMMARY, CONCLUSIONS 6 RECOMMENDATIONS <br />This report consists of slope stability analysis of the existing <br />structure based upon information from the Phase I Inspection Report <br />prepared by Hydro-Triad, Ltd. and the more recent information obtained by <br />technical personnel from Armstrong & Associates, Inc., Project U802849 <br />including piezometer readings showing the highest phreatic water level <br />recorded. Also included is spillway sizing. <br />Preliminary information indicates a desire for the existing dam to be <br />raised to maintain existing storage capacity and allow for the construction <br />of an adequate spillway. Consequently, both the upstream and downstream <br />slopes need to be reinforced to provide adequate gravity resistance for the <br />ultimate stability of the structure. We further recommend that both a sand <br />blanket and a toe drain be included to create an artificial region on the <br />downstream portion of this structure that will be free draining. This <br />drainage blanket will provide for a lower phreatic line through the earth <br />structure and eliminate any potential downstream slope piping problems. <br />We recommend actual field samples be obtained for laboratory testing <br />and analysis to reconfirm and/or modify soil strength parameters assigned <br />for preliminary design purposes. <br /> <br />VI-1 <br />