2006-05-31_REVISION - M1978056 (10)

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6 Vyen~a~d~ a//ve~~i 0~~pe~~ratlon- Du~hem Pft `.'. w.°l. M~411OMI P~e3 -dry density; -direct shear strerx,)th; -grein size distribution; -6quid Emit; and -plastlcity index. Feld observations and gradation test results indicate the majority of the bank material is sand with gravel with a dry bulk density of 115 pounds per cubic foot The internal angel of friction was cakxilatad to be 49 degrees. The residual and peak bn was reported at 0 and 450 pounds per square foot The moisture content varied between 7.5 and 11.5%. A cohesion of 0 was used in sbpe failure calculatlons. The software program SLOPE/W and SEEP/W was used to estlmate statc bank failure safety factors. Mine pit and river flood conditions with rapid drewdown scenarios were simulated as well. These simulations were performed by CTL Thompson. The profile of section 43+40 as shown on Piste C15 (Attachment A) was used to predict safety factors. This section was chosen as ft identifies the presence of a productlon gas transmissi~ line and has substantlal pit side bank height. The soil conditions were replicated to match the soil profile of soil boring B-6. Sbpe failure analyses were ran for the river and mine pit sides of the bank The modified Janbu method was used as it provided more conservatBre safety factors. The river side stability results indicate factors of safety between 4.05 and 5.66. Simulations for static, pseudo static, mine pd flood and river rapid drewdown were performed. The same simulations were run for the pit side of the bank with pkarlated factors of safety varying between 1.99 ar-d 2.35. The author used PCSTABL to evaluate sbpe stability at section 36+40. This section appeared to have the steepest sbpe between the embankment and river of any cross sections presented by Anderson Consulting. Static conditions and river side and pit side