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� <br />� Report ' <br />Short Plat <br />� May 4, 1990 <br />Page 4 <br />� north and soath on Madrona Avenue. I did not observe any evidence of instabiliry of the slope or the <br />lower Whidbey Formacion. <br />� Although the site appears to be stable in its present condition, care should be taken to maintain <br />�his stability, Fill should not be placed on the slope without specific geotechnical engineering. Areas <br />� that have been stripped of vegetation should be protected from erosion, !'his could include <br />hydroseeding or some other ground cover. The vegetation should be maintainad until it is escablished. <br />� FpUNDATI�NS <br />1 I recommend that at a minimum, the structures be founded below a line eactending from the base <br />� of the slope as shown on the cross-�ecrions. Tue cutside edge of the footing shoutd atso be locatod a <br />'� minimum of ten feet horizontal from the slope :urface. The foundations would then be founded withie <br />i <br />the advanced outwash soils. The pu�pose of the line is to keep the foundations below a level thet could <br />' be involved witli fud►re sloughing or surface moven:ent on the slope. A factor of saf�y is included m <br />� this line. <br />� Continuous and isolated column footings shouid have miuimum widths of 12 and 18 �nches <br />t����ly, The footings should be buried a minimum of 18 inches below ttie adjacent grade• For <br />foundacions founded as oudined, I recommend using a soil bearing value of 3000 pounds Per SQuue <br />foot (ps�. 1 estimate total setdements of less tha� •5 inches for these foundation conditions. <br />!The aiternative to standazd foundation design would be to use augercast piling or drilled piers on <br />j this site. The t�enefit of this type of foundation system is that it wonld not require the dcep excavadon <br />� w bury the foundations as described above. Piling or piers should be designed after specific strucwres <br />; have been have t�een developed. <br />EXCAVATION <br />Excavations on site will require temporary cut slopes, pardculazly if standazd foundations are <br />ased. I recommend using the following slope for the site materials: <br />! l:l (H:V) For the advanced outwash <br />1.5:1 (H:� For the recessional outwach and modified soiL <br />These values should be considered guidelines. The accual slope inclinations may require <br />modifications based on performance observed in the field. These embankments should be covered with <br />pl�stic during the wet season to resist erosion. <br />COUVRE'I7'E GEOTECFiNICAL ENGWEERING <br />