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M98177GE <br />A drain system should be included at the bottom back of the toe <br />key and at the back of several benches. This concept is shown on <br />Figure 4. We should observe the key and bench preparation to <br />verify that the key and bench extends into competent material. The <br />drain system should consist of a drain pipe about three (3) to four <br />(4) inches in diameter and surrounded by about three (3) to four. <br />(4) cubic feet per linear foot of drain of a free draining aggre- <br />gate which is surrounded by an appropriate geotextile filter <br />fabric. The drain should be graded to drain to positive gravity <br />outlets. The outlets should be maintained to prevent them from <br />becoming frozen or plugged and equipped with guards to prevent <br />access by rodents or other animals. <br />The fill material should be moisture conditioned to about two <br />percent wet of optimum moisture content placed in thin lifts and <br />compacted to at least ninety (90) percent of the maximum dry <br />density as defined by ASTM D1557, modified moisture-density rela- <br />tionship (Proctor) test. If the compaction equipment used for <br />compaction of the fill has sufficient energy to compact thicker <br />lifts the lift thickness may be adjusted to a thickness capable of <br />compaction by the equipment used but should not exceed a lift <br />thickness of about one (1) foot depending on the capabilities of <br />the compaction equipment. <br />The inclination of excavated cut or placed fill slopes based on <br />our stability analysis will depend on the height of the slope. The <br />height of the slope and the associated slope inclinations based on <br />a calculated theoretical factor of safety of 1.5 are tabulated <br />below. <br />SLOPE HEIGHT MAXIMUM SLOPE INCLINATION <br />(FEET) __(HORIZONTAL TO VERTICAL) <br /> <br />0 to 10 2.0 to 1 <br />10 to 15 2.25 to 1 <br />15 to 20 2.5 to 1 <br />The geotechnical engineering discipline considers a theoretical <br />calculated factor of safety of 1.5 against slope failure as the <br />minimum recommended factor of safety. Slopes with lower factor of <br />safety may have significant long term maintenance costs associated <br />with them. Any excavation cut or placed fill slopes higher than <br />twenty (20) vertical feet should be analyzed on a site specific <br />basis. <br />~Lambcrt ana ~.ssociates <br />GONSUIPNG GEOtEONeiC~L ENGINEERS AND <br />M~TEawL iEST~HG <br />