1329 MADRONA AVE Geotech Report 2022-10-25

• Subsurface Exploration,Geologic Hazard,and lanowicz Property Geotechnical Engineering Report Everett,Washington Preliminary Design Recommendations • favorable dry weather and optimum subgrade moisture conditions. The on-site soils generally contained significant amounts of silt and are not suitable for reuse as structural fill. A representative from our firm should inspect the stripped subgrade and be present during placement of structural fill 'to observe the work and perform a representative number of in-place density tests. in this way, the adequacy of the earthwork may be evaluated as filling progresses and any problem areas may be corrected at that time. it is important to understand that taking random compaction tests on a part-time basis will not assure uniformity or acceptable performance of a fill. As such, we are available to aid the owner in developing a suitable monitoring and testing frequency. 11.0 SHORING Given the subsurface and topographic conditions present and the proximity of the adjacent existing house to the southeast,we recommend the use of shoring such as a soldier pile wall to facilitate basement level excavation for excavations greater than 4 feet. The soldier piles should extend below the base of the colluvium and landslide deposits and embed into the hard non-glacial sediments. We recommend that the soldier pile wall be designed for a height of up to about 15 feet including the depth of the colluvium and landslide debris and anticipate this may require one row of tiebacks. This should extend for the length of the excavation and .should return on each side until the cut daylights,to protect the sides of the excavation. If tiebacks are required, the tiebacks may require a setback area or an easement for the anchors that extend offsite. As an alternative anchors may have to be steeply inclined to avoid extending onto adjacent private property. Incorporation of this setback could result in a • residence having a smaller configuration than desired. The wall may be designed using the following "at-rest"and "passive" equivalent fluid pressures (EFP). Due to the loose density of the colluvium, at-rest retained earth pressures are recommended to limit the amount of wall movement. The recommended wall EFP have been selected to mitigate the existing landslide hazard in the proposed building area, and should result in factors of safety against landslide movement of at least 1.5 for static conditions and 1.1 for seismic conditions. • At-rest equivalent fluid pressure equal to 98 pounds per cubic foot (pcf) triangular pressure distribution should be applied to the contributory area of the center-to-center pile spacing. This pressure extends to a depth of 15 feet below the ground surface. • For walls that are allowed to yield an amount equal to 0.001 times the height to develop an active condition, the active equivalent fluid pressure equal to 61 pcf triangular pressure may be used. Distribution should be applied to the pile spacing above the cut line and one pile diameter below. May 10,2018 ASSOCIATED EARTH SCIENCES,INC. NSfrd-170649E002-2-Projectrt20170549lKElWP Page 14