Laserfiche WebLink
<br />Memo to Susan Burgmaier <br />Southfield Coal Refuse Pile <br />page 3 <br />be compressed by the overburden placed above it. In this case between zero feet <br />(0 psf loading) and 75 feet (6,375 psf loading) maximum thickness of the pile. <br />What are the realistic consequences of this material character and placement <br />methodology for the geotechnical engineering construction of the Southfield <br />Mine coal refuse pile? The placement and compaction methodology currently <br />being applied will probably result in a layer-cake assemblage of 1 foot thick <br />fine refuse between two to three foot thick layers of coarse coal refuse. The <br />coarse coal refuse will be between 90% and 100% relative maximum density. <br />The fine coal refuse layers will compress with burial, reaching ultimate <br />densities commensurate with the overburden pressure applied in relation to <br />their depth in the pile. Successively deeper layers will become more dense. <br />With increase density, TerraMatrix's testing demonstrates the fine coal refuse <br />will become increasingly stronger ("more resistant to shear displacement"). <br />Precise analysis of a structure of this sort can be significantly challenging. In <br />order to render the exercise manageable it is appropriate to make simplifying <br />assumptions. TerraMatrix has chosen to model the pile as comprised solely of <br />fine coal refuse with homogeneous properties. They have used the angle of <br />internal friction (38 degrees) and the cohesion (50 psf) determined by their <br />laboratory testing. They have chosen to consider a combined waste unit weight <br />of 79 pcf. An appropriate weight for such an analysis would be a pro-rated <br />average of the weights of the fine and coarse refuse, prorated in relation to <br />their composition of the overall refuse. This weight appears to be low in <br />relation to the observed densities determined in the field. It would be <br />appropriate for TerraMatrix to justify it's theoretical refuse weight choice at <br />greater length. <br />I suspect, without having duplicated the stability analysis, that a 10 pound per <br />cubic foot (pcf) to 15 pcf increase in material weight will not drive the <br />theoretical pile to below a static slope safety factor of 1.5. However, with the <br />aid of the computerized analysis, completion of such a "sensitivity" analysis <br />requires a relatively minimal effort. <br />