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~~~ • Mr. Brent Anderson Page Three October I, I990 IMPROVING DRAINAGE AT THE TOE Of THE SLIDE Providing effective drainage at the toe of the slide would help to prevent any buildup of significant pore pressures within the slide. At present, the open drainage ditch at the toe of the slide serves this purpose adequately. However, the drainage ditch also carries runoff from the road and upgradient areas across the toe of the slide and could result in; erosion of the toe. Maintaining a stable tae is important to assuring overall stability of the currently stable slide mass. Two measures for improving toe conditions are recommended. First, a Swale should be constructed across the road above the slide. This Swale would. intercept all up gradient cut side drainage and divert it to the existing i drainage ditch on the fill side of the roads= This would minimize erosion of the toe of the slope. Second, a 2' x 2' rock drain wrapped in filter. fabric should be constructed across the -toe- of__ihe slide. __The drain.=` i should be constructed by excavating _a trench at the toe of the-slide wifh p a backhoe, installing filter fabric and drain materials in the trench, and ~ ` recovering the .trench,._Thi_s would insure adequate drainage at,the toe,of` - -- - the slide regardless of natural sedimentation or any additional minor,:' movements of slide material. 'The attached figure shows a cross section of `" • the proposed drain. INSTALLING A TOE BUTTRESS In a previous report dated IO/23/85, ACZ recommended installation of a toe buttress in this area. Construction of the toe buttress was deferred pending development and implementation of stability monitoring measures. At- tfiis time it-appears-that-a,large toe buttress is unnecessary as the ~ ~. slide-has stabilized itself above the"road.; The current configuration`' j' would provide the best alternative for long term use of the road. Therefore, at this time a small buttress.,of dimensions _approximately_2'~ _ high x 3' wide is recommended. The purpose_of_~ths.buttress is more_to._- provide cover and protection for the drain at the toe of the slide than to:- add weight to the toe. ANNUAL INSPECTIONS The slide area should be inspected annually for the next five years by a -? competent professional. Annual inspections would provide a record of the conditions of the area as well as give timely warning of any changes in stability. Very truly yours, ACZ INC. • C~~ ~~~ Conrad H. Parrish Colorado PE 17932 CHP:rce attachment