4841 GLENWOOD AVE 2021-06-09 - Laserfiche WebLink

UI 111 ► � Mil RILEYGROUP August 21, 2019 Ms. Isha Daramy 1501 150th Place Southwest Lynnwood,Washington 98087 RE: Geotechnical Recommendations 4841 Glenwood Avenue Everett,Washington RGI Project No.2016-072 Dear Ms. Daramy As requested, The Riley Group, Inc. (RGI) is providing this letter to provide geotechnical recommendations for the design and construction for rebuilding the existing block retaining wall at the site. Project Description The subject site consists of an existing retaining wall constructed on the west side of the lot at 4841 Glenwood Avenue in Everett, Washington. Currently the site is occupied by a single family residence.The location of the site is shown on Figure 1. RGI understands the retaining wall was permitted but the permit was not finalized at the time of construction.The wall is also not constructed with the appropriate batter on the wall per the plans for the wall construction. There is also a concern about the use of the native soils as backfill and if the soil was properly compacted and drainage installed as recommended in the plans. Soil and Groundwater Conditions RGI completed two test pits behind the wall to determine the length of the existing grid and quality of the backfill soils.The locations of the test pits are shown on Figure 2.The soils observed behind the wall consisted of silty sand with gravel to silty sandy gravel. The surface soils were loose to medium dense and become loose and wet to saturated from five to seven feet below the existing grade with severe caving observed. Voids were also observed below the existing concrete pavement behind the wall indicating settlement of the backfill soils. The southern test pit, TP-2, was extended to the back of the wall to determine if drainage was provided as recommended in the plans. The soils were mixed with drain rock but no drainage zone was observed behind the wall. Geogrid was encountered, however it was two feet shorter than the design recommended. Retaining Wall Design Based on the conditions observed in the backfill for the existing retaining wall, the wall is not stable as constructed. We recommend rebuilding the wall as a gravity wall using the blocks onsite. This will require removing the existing blocks and restacking the blocks in a gravity configuration. The blocks onsite are similar in size to Ultrablocks®and the Ultrablock®Wall design program was used to design the gravity wall. The design includes a fire truck loading on the pavement above Corporate Office 17522 Bothell Way Northeast i Bothell,Washington 98011 Phone 425.415.0551•Fax 425.415.0311 www.riley-group.com