1209 MADRONA AVE 2016-11-17 - Laserfiche WebLink

Geotechnical Engineerin� Evaluation Packer Property Retaining Walls and Steep Slope Evaluation Everett, Washington �,andsiide �-iazard NGA File No. 870113 March 11, 2013 Page 7 "I'he criteria used for evaluation of landslide hazards include soil type, slope gradient, and groundwater conditions. A steep northwest-facing slope with gradients in the range of appraximately 20 to 60 degrees (35 to 173 perceni) is located on the northwestern portion of t1�e property. "I'he cc�re of the slape is inferred to consist primarily of inedium dense/stiff or better na#ive silty sand and silt deposits. Inclinatioi�s of up to 60 degrees on the slope indicate hibh stre�Zgth and internal friction angle within th.e underlying soils. Relatively shallow slougl�ing failures as well as surf`icial erc�sio�i are natural processes and should be expected on this slope during extreme v��eather coi�ditions as has been observed recently and in the past. It is our opinion that there is sicnificant potential fo: erosion, soil creep, ai2d shallow failures withit� the loose surficial soils on the slope. There is also a siD ificant poiential fc>r the existing lower waIl to fail under the current srte conditions if conditions are not improved as recornmended in this 1•eport. Proper slope rnanagement, along with new reiaining wa11 installation and s.lope and drainage inlprovements as recommended in this report sk�ould improve the site stability conditions. CONCLUSI011TS AND RECO�VIl!'��NDA'�'I�NS General In our apinion, the existing tiered retaining walls appear to generatly be in a stable condition and have experienced little movement throughout the yeai•s, with the exception of a localiaed sectian of one the w�ails which experienced failure. We have provided repair reeommendations for this failing wall in the Failing Wall Repairs subsection of this report later in tliis report. It is our opinion fhat the recent slidin� acti��ity was not caused by ar influenced by the presence of the block walls on the slope. The recent slope activity is rather a natural occurrence that v��as direcily related to the steepness of the slopes, tlie makeup of the surficial soils, and recent heavy rainfalL It is also our apinion that ihe recent slides may have been partially znfluenced by the lack of proper drainage and suitable vegetation on the neighboring pro�erty. The slope on the neighboring property is covered with blackberry bushes, which dc� not provide adequate root support for the surCicial soils. /�tELSOM GEQTEGHAItCAL ASS�CdATFS, !ldG.