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3.0 POTENTIAL STABILITY PROBLEMS • 3.1 EXISTING FACILITIES 3.1.1 Fills A series of fills have been constructed to produce the benches on which the existing mine facilities are located. These fills appear to have been constructed with a minimum of compaction, and with outer slopes at the angle of repose of the fill material. The highesC of these fills, the crushing and screening level fill, has a maximum height of some BO- feet above the original ground surface (Plate 4). Locally, some of the fills appear to have been constructed on quite steeply inclined natural ground surfaces, such as the fan level fill shown on Geologic Section C-C' (Plate 5). • The safety factor of fills constructed at the angle of ~' ~ re ose is alwa s close to unit p y y, although the most critical po- tential failure surface may be quite shallow and therefore may not be of particular concern. Fills constructed of loose ma- terial are likely to undergo Large settlements which may be of importance not only to structures located on the fill but may also influence the overall stability of the fill. When fills arc located on an inclined surface, there can be the potential £or failure along the contact of fill and natural ground sur- face. The inclusion of any water pressures, or additional load- ictg, such as may be induced by placing a surcharge on the fill or by earthquake forces, may also influence the stability of the fill; these factors have been evaluated in our stability analyses. The origin of the fill materials is believed to be £rom the rock and soil cuts constructed at the site. The small • amounts of coal present in the fills are probably due to in- corporation of material from around coal outcrops. There is no evidence of mine waste or significant quantities of trash being. incorporated into the fill. -l'- ~¢o-NVOao ca+wtnr~c. ir+c. I I