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A 2D limit equilibrium slope stability analysis calculates the factor of safety against failure assuming <br />a plane- strain condition. Therefore, it is implicitly assumed that the slip surface is infinitely wide, <br />and thus 3D effects are negligible because of the infinite width of the slide mass. This assumption is <br />reasonable in cases where the width to height ratio is greater than 5 (Stark, 2003). In the case of the <br />RPE East the approximate width to height ratio is about 2 to 3, and thus the impact of the 3D effects <br />are significant. As a result of this determination, a deformation analysis with FLAOD was <br />performed to assess the proposed slope conditions and evaluate the 3D effects which more accurately <br />assess the stability of a slope with well - defined 3D geometry. In other words, the actual geometry <br />was modeled and the effect of the shear resistance along the flanks of the potential failure surface <br />was determined. Three - dimensional analyses are significantly more complex and consequently are <br />not often performed, but they more accurately represent field conditions. <br />2.2.2 Model Parameters <br />The two most important materials relating to the stability of the RPE East refuse pile are the refuse <br />itself and the underlying colluvium. The bedrock underlying the colluvium is generally sandstone <br />and siltstone. While zones of shale may be present within the stratigraphy in the area of the refuse <br />pile, they are anticipated to be unsaturated. The critical materials (refuse and colluvium) are <br />addressed in the sections below. The parameters used in modeling for these and the other materials <br />are found in Table 1. <br />2.2.2.1 Refuse <br />As stated above, four samples of refuse generated by the new CPP were collected from the existing <br />RPE area. Laboratory tests performed on this material included moisture content, Atterberg limits, <br />dry density, organic content, standard Proctor, fully- softened direct shear, and hydraulic <br />conductivity. The 3- inch -minus material was classified in the laboratory as a silty gravel with sand <br />and coal (SM) based on the gradations which included sieve and hydrometer. The four samples <br />were very well graded, and generally compared well with each other. The percent passing the #4 <br />sieve ranged from 35.1 to 52.4% and the percent passing the #200 sieve ranged from 12.3 to 18.4 %. <br />In addition to the gradations carried out on the 3— inch -minus material as- received from the field, <br />some of the material was pulverized to determine the degree to which the particles broke down under <br />various degrees of compaction. While the material in the RPE was compacted during placement <br />(sample from the SE corner of the RPE), additional compaction was simulated using a standard <br />Revised July 21, 2011 raj 5 <br />gjG Lt <br />P.\Mp1s \06 CO \26 \06261003 RPE E Permit Mod Support \WorkFlles\Permit Apphcation \Text \Exhibit 82 RPEE design 2011 -07 -21 TR 127.doc <br />