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r <br />Mr. Dale Gustafson <br />October 11, 1994 <br />Page 4 <br />particle size of 2" and no more than 50% material finer than a #4 sieve or 3% finer than a #200 <br />sieve This type of material is free draining, exhibits very little shifting whei. frozen, and is <br />easier to compact in confined spaces such as expected at this project site. We recommend <br />placing the granular fill in lifts no more than 6" in thickness with vibratory compacuon of each <br />lift Care should be taken in choosing compaction equipment which has sufficient energy for <br />effective compaction yet does not have excessive energy or weight to cause significant shifting <br />of the wall facing stones during the gravel compaction process. A porous geotextile separauon <br />fabric is recommended to separate the gravel fill from fine grained native soils at surfaces where <br />seepage from the soil into the gravel can be expected. This includes beneath the topsoil layer <br />placed over the gravel. <br />Our computations indicate the critical, or governing, factor for wall stability is lateral sliding <br />of the reuining wall base. In order to attain the minimum recommended factor of safety, we <br />recommend the following minimum depth (distance back from the back of the facmg stone) of <br />geogrid-reinforced gravel. <br />WaU Height (ft.) <br />Depth of Reinforced Backfill Zone (ft.) <br />Level Slope <br />Behind WaO <br />2.5:1 Maximum <br />Slope Behind Wall <br />2 2.6 3.4 <br />4 4.5 6.8 <br />6 6.8 10.1 <br />8 8.9 - <br />For wall heights between those listed above, you can interpolate in direct proportion to amve <br />at fninimum reinforced backfill zone depths. <br />We recommend using a geogrid at least equal to the specifications of Tensar UX1500 (SR-^ <br />uniaxial material for slope reinforcement. For at least some fastenmg of the face stone to me <br />reinforced backfill, we recommend extending me geogrid 8" to 9" mto me stone cou^ j <br />at the geogrid layer level. You should realize this connection relies only on me mcuoi^ <br />resistance of movement between me stone and geogrid material. Thus, care should be t^en <br />when moving equipment or heavy objects near me facing stone, so me stone is not s e <br />damaged.