Laserfiche WebLink
,: �"�'" o+t;.e <br /> ..� - , �C�,sPP'ia-?i���Ys�,��.��?s:Y`'�'w�;.� 3�^.;,:i. �s�; ^^� � .. .. .��' . . <br /> . ., ... � . x ,%C'TF�ygo,�'•* _. y_ <br /> Allestad <br /> June 18, 1990 <br /> EVALUATION AND RECO?fliIItDATIONS <br /> ��eneral Site Evaluation <br /> aased on review of published geologic mapping and the soils <br /> observed on the site it appears that the site lies near a <br /> contact between glacial till deposits and advance g.lacial <br /> outwash deposits. These soils were deposited and <br /> consolidated during the Vashon glaciat:.on, the last glacial <br /> advance into the Puget Sound area appi•oximately 13,500 to <br /> 15,000 years ago. The natural soils encountered in our <br /> onsite explorations consisted of up to about 4.5 feet of <br /> medium dense weathered soils unc?=rlain by very dense less <br /> weathered till-like soils. <br /> The site is bordered by a steep slope on the east side. We <br /> did not observe any ground cracks or other indications of <br /> gross instability but considering the steepness of the <br /> slope, the granular nature of the subsoils and the presence <br /> of fill soils, the potential for shallow slope failure is <br /> considered to be high for the east slope in its existing <br /> condition. As with any hillside development the owner must <br /> be willing to accept some risk of possible future slope <br /> movement which could result in damage to improvements on the <br /> site or to neighboring properties. However a braced <br /> basement retaining wall will tend to buttres the slope and <br /> effectively reduce the unsupported slope height in the <br /> ; vicinty of the proposed residence. It is our opinion that <br /> no special toe-of-slope setback is required for the proposed <br /> ' structure location assuming that a basement retaining <br /> wall(s) designed and constructed in accordance with our <br /> recommendations is provided to support the slope. Existing <br /> slopes adjacent to the structure should also be buttresed to <br /> flatten them to gradients of 2:1 or flatte;:. <br /> Results of our explorations and observations of the site <br /> indicate that most of the building site is underlain by a <br /> varying thickness of existing fill containing organics and <br /> debris. In our opinion these fill soils are not suitable <br /> for structural support. Structural loads should be <br /> transferred through the fill and medium dense natural soils <br /> • to the dense/hard natural soils. This can be accomplished <br /> by simply deepening th�: footings or by a monolith of lean <br /> mix concrete where fills are deep. <br /> The following subsections present our recommendations for <br /> desiqn of foundations, retaining walls, site qrading, site <br /> drainage and erosion control. Also included are <br /> recommendations for plan review and obseraations and testing <br /> during construction. <br /> Page No. 4 <br /> Projact No. 90-122-01 <br />