1209 MADRONA AVE 2016-11-17 - Laserfiche WebLink

Geotechnical Engineerine Evaluation Packer Property Retaining Walls and Steep Siope Evaluaiion Everett, VJashingcan NGA File No. 870113 March 11, 2013 Page 8 Even thaugh the walls appear to be stable, it is also our opinion that the walls were nof constructed in accordance ��ith current engineering standards or with the manufacture's recommendations for this type of wall. Similar engineered wall systems of this hei�ht and orientation are typically constructed with larger, heavier blocks i�rterlocked with fiberglass pins, andlor geogrid reinforced backfill. To improve the existing walls to meet engineering standards would likely include removing the walls and creating si��ifcant cuts and fills on the sloping area. It is our apinion, that removal of the walIs and re-grading of the slope are unfeasible due to the limited access conditians and «�auld likely cause additional stability issues than if tne walls are leit in their current state. Tllese wa11s have performed well since their instailation but could ea:perience soine settlement and movement in the futuxe, as has been experienced in the eastern sectian of one the walls. It is our opinion, however, that these walls shauld be lefi as is to reduce adverse impacts to the slope. If future urall distress v�7ere to occur, �7e recommend that u�e be retained to evaluate these occurrences on a case-by-case basis to provide specific recommendatiazas for repairs to the u�alls. ��e recommend that drainage for tl�e walls be maintained, and the condition of the wa21s be obsenTed tlu-oughout the years for any changes. It is �ur opinion that the recent landslide and stability issues observed below the walls could significantIy impact the existing wall system if conditions are not impro��ed belo�� the u�alls. Based on our obsen�atians of the eurrent conditions in the vicinity of the recent Iandslide, it is our opinion tliat the landslide was Izkely due to weak surficial soils on the steep slope on both properties becoming saturated during tlie recenti relatively wet winter and in turn experienced a reduction in tlieir shear strength leading ta the landslide. The n�aterial tlaat slid off the neighbor's steep slape emanated from a considerably higher vertical etevation than the Packer property below. Although, it is our opinion that the observed slide only affected the loase su�cial soils rather than the core of the slope, it is likely that the slope movement will continue and could eventually impact the walls if adequate nleasures for stabilizing the affected areas on both properties are nat imp]emented as recommended in tlus report. Based on our explorations and site observations, we reco�nmend the use of a`light'' retaining wail to provzde permanent support for the steep slope immediately below the I�wer western retaining wall in the appro�mate area of the recent landslide, along with erosion control and drainage systems to bc utilized above and below the retaining wall. Also, the surficia] stability within the remaznder of the steep slape should be improved throug� the use of erosion control s}�stems. We recommend Chat the new retaining wall be located to stabilize the slide area to the w�estem property line and e�tend eastward past the slide to IVELSOI� GEOTECHlV1CAL �6SSOCiATES, fJVC.