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Northern <br />Coal <br />U Company <br />Page 3 <br />CMLR July 23, 1980 N,emo <br />fiunderlying sandslt~This`.`,trench`will be constructed so that it will"daylight"iintto~he <br />F.° ~ ~ a~ . .... <br />,natural drainag couase.'~The trench will be lined with a geotextile, such as Mirafi <br />1405 or equivalent, and a coarse graded gravel or crushed rock used as backfill. The <br />fill material will have less than 5% passing the number 200 sieve, in order to allow. ,. <br />good drainage. a trench~drain;should only be required in:.th'e;azea~of':P-2;and <br />~whe~re the high~,g~ ound oratei•;readings were reported.. <br />Slope Stability A~nalysis~'" <br />r <br />Material pazameters utilized in the stability analysis have been adopted based on <br />laboratory tests of materials from the site which will form the foundation and spoil <br />pile fill. The unit weight determination which has been conducted on selective <br />samples from the project site has teen included on Figure 13.1.1, Sheet 1, which is <br />attached. The modification is noted. The unit weight for the waste material used in <br />the stability analysis was 106 pounds per cubic foot. This corresponds approximately <br />to 92% of the estimated compacted dry density. liitspecifying an?.85%edens~ i <br />..: .. <br />~noi unrealistic~~to'assume that an average compactioneffort m the range of~42%;'v"ei4~ <br />~be achieved in the spoil P}~1e'~' In;fact; the heavier: spoil; pile should;`produee^a.lower <br />~safe;ty factor in the stability `analysis, assumtng.'a~higher density;in;the spoil,pi~'e is <br />xi~~ <br />conser-vative. =~'I ~ <br />In evaluating the slope stability for the proposed waste pile, we have been very <br />conservative in assuming :hat the entire pile will consist of a ~•11ey fill material. , <br />with the low shear strength properties shown on Figure 13.3.2 and Figure 13.3.3. •" <br />~' <br />The actual shear strength properties of this waste fill should be higher, pazticularly ~ ~;: <br />• ~~~,, <br />if durable rock fill is present. ~ .~ ;,:,. <br />i <br /><j Pseudo, Static Stability Analysis <br />n <br />~+ ~ he ~coefficienti~ lo.f~yseisa~city of ~O.D2 <br />published in the "Recommended Gu <br />