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• - 2- <br />For the purpose of this analysis we considered a 40-foot high haul road <br />embankment constructed using overburden. We performed slope stability <br />analysis using the Janbu chart method. Our analysis considered a <br />maximum embankment slope of 2:1 (horizontal to vertical) as specified by <br />the Permanent Regulatory Program. We analyzed the haul road embankment <br />with and without haulage trucks traveling across the embankment. For our <br />analysis with a haul truck traveling across the top of the embamkment, we <br />considered that the truck would induce a uniform load of 10 ksf across <br />the top of the embamkmento The results of our slope stability analysis <br />indicates a factor of safety of 3.4 fora 40-foot high embankment with <br />2:1 (horizontal to vertical) slopes without haul trucks. A factor of <br />safety of 2.1 was computed when the surcharge load was applied at the top <br />of the embamkment. Both of the safety factors computed from our analysis <br />are greater than the required 1.25 minimum. <br />In addition to performing strength testing, spoil materials were also <br />subjected to slake-durability tests. The results of these tests indicate <br />percent losses ranging between 4 and 16 percent, which indicates the spoil <br />materials are fairly competent with respect to break down due to reaction <br />with water. However, based on our observations, the overburden will break II <br />down into fine-grained soil when subjected to traffic loads. We have ob- <br />served at the Kerr Mine that occasional resurfacing of haul roads with <br />• sandstone overubrden provides a serviceable surface. <br />The opinions presented in this letter are based on observations over the <br />past two years at the Kerr Mine site, as well as field and laboratory in- <br />vestigations for previous studies at this site. We can provide the detailed <br />backup data, if desired. If we can be of further service on this project, <br />please call. <br />Very truly yours, <br />CTL/THOMPSON, I <br />By W C... r ~- <br />William C. H / ann, Jr. .Proje <br />i <br />Reviewe~ii v:_ r•• -. 1~ <br />on, <br />107 <br />WCH:RWT:dm <br />(3 copies sent) <br />• <br />