13 46TH ST SW 2016-01-01 MF Import

� DAVID �. NELSON AND ASSOCIATES, INC. � Consulting Engineering Geology October 6, 1992 Project No. 9892 � Page 6 The slopes on this propErty have receded over the past centuries � due to long-te.rm slope erosion and surface sloughing processes. These very slow processes should be expected to persist at their current rate. Development related improvements such as site I drainage control systems tend to lessen the impact of surface and ground water on the slopes, and will slow the rate of backwasting to an even slower rate. Also, rer,ioval of any f.ill or debris from the top of slope, and protection of exposed soil areas from � erosion will greatly increase the overall slope stability. Development Considerations jUncertainties related to building along steep slopes, and in particular unstable areas, are typically addressed by the use of i I setbacks. The purpose of the setback is to establish a "buffer zone" between dwelling areas and the slope marqin so that if a slope failure were to occur, the likelihood of dwelling � involvement would be minimized. In a qeneral sense, the greater 9 the setback, the lower the risk. From a qeological standpoint, � the setback dimension is usually based on certain physical slope �haracteristics, ea. , slopa height, surface anglP, material � composition, hydrology, etc. Other factors such as historical slope activity, rate of regression, type and desired life span of the development are important considerations as well. IBased upon our observations of the stable nature of the slopes, and the pru�osed development, we recommend using the minimum building setback oi 24 feet from the located top-of-slupe "line" , � as approximately shown on the enclosed maps, for foundations placed at the surface. Alternatively, we recommend that a 15 foot building setback can be used, provided that foundations are � placed a :ninimum of 5 feet below natural soil grade elevations. The use of this type of setback is referred to as an "effective" setback, where additicnal foundation depth into the native soil to be at the determined stable slope angle (i.e. 2H: 1V) creates a � proper setback from the slope face. These recommended setbacks are graphically shown on the enclosed Soil Profile, sheet M-2 . I Protection of the setback and steep slope areas should be perf.ormed as required by the City of Everett. Specifically, we recommend that the setback area not be used for placement or storage of fill materials, including "temporary" excavation � spoils from building area preparation and excavation. Any development or encroachment into the setback areas should De evaluated by a specific geotechnical investigation. Reductions I in setback areas are possible, but onl.y with the addit�onal geotechnical evaluation, including explorations. It should be / understood that the closer the structure is to the slope, the � more risk there is of future distress. 1 � .__ - — — -- -— _ __ __— ---- ; _ _ _._.