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<br />Page 2 <br />Fred Santa <br />Dean Masseu <br />February 6, 1980 <br />Spoil Spoil Colluvium Saturation Factor of Percent <br />(b Density ~ Level Safety Variatio•: <br />37° 105 40° Below Toe 2.14 ~~ 25~ <br />37° <br />37° Z25 <br />115 26° <br />26° Below Toe <br />10' Above Toe 1.70 <br />I.SB ~ 35p <br />J 130q <br />37° 115 26° 50' Above Toe 0.93 ., <br />The cumulative influence of data inaccuracy could result in significant <br />error in the calculated factor of safety. No soil testing was performed <br />by the consultant in the preparation of this analysis, Strength parameters <br />for both the colluvium and the spoil material were assumed or extrapolated <br />from penetration testing. <br />2. The slope configuration was assumed by the consultant to be that proposed <br />in a letter from Colocavo Coal Company to the Tasic Force of the Office of <br />Surface Mining, dated August 29, 1977. Field inspection personnel of the <br />Division have expressed doubt regarding conformance of the as-built fill wit.'-. <br />that original proposed configuration. Variations of the as-built fill from <br />the analyzed proposed configuration could render the analysis inaccurate or <br />potentially insignificant. <br />3. The consultant states t.'7at; "It is not known if the topsoil and organic <br />matter were removed prior to placement of~the fill." However, the analysis <br />assumes remoc~al of the topsoil. The mathematical model does not include an <br />appropriate low shear strength horizon to reflect its possible existence. <br />-.. The consultant assumed strength data for the colluvium underlying the <br />spoil fill based upon correlation from standard penetration tests taken during <br />drilling. This correlation technigue is crude. The author further observed <br />that the addition of the spoil pile surcharge would increase the colZuvium <br />density. He theorizes that; "The increase in density will also increase the <br />angle of internal friction (of the coiluvium) and the apparent strength-" <br />Research into the shear strength of fill materials of cohesionless character <br />has demonstrated that increase in confining pressor=decreases observed angles <br />of internal friction. (Marsal, Leps, ldarachi) Fer this reasoa tf±e performance <br />of comparative calculations of factor of safety assuming a 40° angle of <br />friction as a possible upper bound of strength seem inappropriate. <br />S. The consultant assumed shear strength parameters for the urderZying bedrock <br />based upon analysis of "weathered material found further upslone". No <br />materials classification is presented to attest to the propriety of this <br />e:rtrapolation. <br />(cont'd1 • <br />