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<br />J. J. Dudash - 2 - June 10, 1998 <br />In the design of the portal bench, BRL accepted the increased risk of shallow slope <br />failures. The DMG was aware of this fact. The site was constructed during the summer <br />1997. The critical time for slope instability is during the spring of the year. With minor <br />exception, the cut and fill slopes on site were stable during the spring of 1998. <br />The subject shallow slope failure could be considered an anomaly. A plane of <br />weakness may be created either by a soft interval in an otherwise uniform formation or <br />by a weak layer in a stratified formation. The weak layer in this case would be a soft <br />clay stratum. There is no evidence that pore water was a factor in the shallow slope <br />failure. <br />Since the overall slope of the final slope surface is slightly flatter than the pre-slide <br />surface, it should be slightly more stable. However, further shallow slope failures may <br />occur. As stated above, BRL accepted the risk of shallow slope failures by its use of <br />1.5h:1v cut slopes. <br />Additional stability analysis are not considered necessary. Both BRL and the DMG <br />should recognize that the portal bench cut slopes have a relatively low factor of safety. <br />Throughout the original permitting process, the DMG emphasized the importance of the <br />stability of the reclaimed surface but indicated BRL could assume some slope instability <br />risk during the operational phase of the project. <br />BRL has visually monitored the slide since it occurred in early March 1998. The slide <br />has been stable since that time and the slide has not had an adverse affect on health, <br />safety or the environment. <br />Please call if you have any questions. <br />Sincerely, <br />~~~ <br />J. E. Stover, P.E. <br />Consulting Engineer <br />cc: Wm. A. Bear, Jr. <br />