2013-09-16_REVISION - M1990057 - Laserfiche WebLink

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Mr. Michael Cunningham CDRMS September 16, 2013 • Density of Colluvial Material (yo) yo = (Ss * Y,,)/(l +e) where: e = void ratio (@ 30 %) = 0.30/(1 -0.30) = 0.43; Sr, = specific gravity = 1.65 Ib /ft3; yw = unit weight of water = 62.4 Ib /ft3 Yo = (1.65 *62.41)/(1 +0.43) = 72.0 Ib /ft3. • Weight of water per Unit Volume Displaced by Solid Particles (yj 71= 7,/(1 +e) = 62.41/(1+0.43) = 43.6 I b /ft3. • Submerged Unit Weight (ym) Ym = 7o - 71 = 72.0 — 43.6 = 28.4 lb /ft3. 0 Gradient of Aquifer (i) Actual gradient is measured as the vertical drop from the top of the aquifer on the east side of the embankment (measured at approximately 5 ft above the TSF floor) to the top of the aquifer on the west side of the embankment (measured at grade with the TSF floor). Note also that there is a 1 ft drop of the TSF floor on the west side relative to the east side. Therefore, the total vertical drop is 6 ft over a TSF floor length of approximately 180 ft. i = 6 ft/180 ft = 0.03. • Critical Gradient (i,t) ict = Ym / 7w = 28.4/62.4 = 0.46 • Factor of Safety Factor of Safety = i / ict = 0.46/0.03 = 15.3 The analysis shows that in colluvial material at the TSF, the aquifer must drop vertically 0.45 ft per 100 horizontal feet for embankment failure to occur. The actual gradient, calculated as 0.03 is approximately 1/15th (or 7 %) of the critical value. By applying the geonet over the weep, and extending down the slope of the embankment and across the floor of the TSF 10 ft, no hydrostatic pressure will develop on the slope (reference figure provided in Adequacy Review No. 2 Response dated 16 August. The ratio of water infiltration (outflow) area (10 ft x 100 ft = 1,000 ft2) to weep (inflow) area (6 in H x 100 ft L = 50 ft2) is 20 to 1, therefore the weep water will dissipate before allowing any hydrostatic pressure to develop beneath the GCL on the floor of the TSF. RECEIVED `;'1' 16 ?n9 DIVISION OF RECLAMATION MINING AND SAFETY