4320 THOMSON AVE GEOTECHNICAL ENGINEERING REPORT Geotech Report 2023-08-10

GeoTest Services, Inc. 4320 Thomson Avenue, Everett, WA March 17, 2022 Project No. 22-0285 pressures given in Table 1 includes a safety factor of about 1.5. Passive pressures acting on the buried portion of a soldier pile are assumed to be acting against three times the diameter of the grouted pile. GeoTest recommends that piles be installed at least 10 feet below the planned excavation level, although deeper installation may be required to generate adequate passive resistance to achieve acceptable factors of safety in the design. GeoTest generally anticipates an embedment depth of between 2 and 2.5 times the exposed height of the wall for conventional, cantilevered soldier pile walls. Shoring Wall Construction Observations GeoTest should be present to observe construction activities and confirm that the subsurface conditions are as anticipated. GeoTest expects that special inspection will be required by the governing jurisdiction and that periodic observation and inspection of the wall during construction will be required as a condition of the construction permit. GeoTest anticipates that inspection services will include pre -drilling of the pile, installation of the pile, grouting of the pile, top -down excavation, placement of the lagging, placement of fill behind the lagging, and installation or placement of drainage systems. GeoTest is available to provide these services as part of a separately negotiated serviced agreement. Once the shoring wall has been completed, final documentation such as as -built drawings and a final summary letter (if required by the City of Everett) will be the responsibility of the wall designer. Catchment Wall A short ecology -block catchment wall will be constructed on the western, upslope portion of the subject property. It should be noted that this structure is a maintenance or erosion control feature, as opposed to a life -safety element. It should also be noted that this catchment wall is not intended to function as a retaining wall, as it would be constructed out of modular blocks. GeoTest understands that the maximum planned wall height is 3 feet (exposed height). We have presented a typical wall configuration for a 4-foot-high wall (including embedment) in Figure 6 of this report. The batter of the wall is approximately 9.5 degrees. The wall is exposed at least 1 foot above the existing slope to provide catchment protection. It will be necessary to periodically remove any soil that accumulates in the catchment area to provide continued protection. The wall should be founded on a minimum 6-inch-thick compacted crushed rock base pad. The base block should be buried at least 8 inches to provide kick -out resistance at the toe of the wall. Proper wall drainage is necessary in maintaining a stable wall. A cleared crushed rock (no fines) drainage layer or blanket located behind the wall should consist of a 12-inch strip extending from the base of the wall to within approximately 12 inches of the top of the wall and wrapped with a non -woven geotextile fabric such as Mirafi® 140N or industry performance equivalent. The fabric 11