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

GeoTest Services, Inc. 4320 Thomson Avenue, Everett, WA I• March 17, 2022 Project No. 22-0285 Table 1 Assumed Soil Parameters for Retaining Wall/Soldier-Pile Wall Design Parameter Value Crushed Rock Base Unit Weight —135 pcf Friction Angle — 401 Native Weathered Advance Outwash* Dry Density —120 pcf (0 — 3 feet BGS) Wet Density —130 pcf Friction Angle — 30' Dry Density —130 pcf Wet Density —140 pcf Active Earth Pressure — 35 pcf (Level Backslope) Native Advance Outwash ** Active Earth Pressure — 60 pcf (Assume 2H:1V Backslope) (3 —10 feet BGS) At -Rest Earth Pressure — 55 pcf Passive Earth Pressure — 350 pcf Coefficient of Friction — 0.35 Friction Angle — 340 Structural Fill Unit Weight —135 pcf (Pit Run Sand and Gravel)** Friction Angle — 350 Allowable Bearing Capacity (Medium - dense to Dense, Native Soils or 2,500 psf Structural Fill placed atop competent, properly prepared subgrade) Notes: 1. psf — pounds per square foot; pcf— pounds per cubic foot 2. * Wall Backfill or Retained Soil 3. ** Wall Backfill, Retained Soil, or Foundation Soil 4. Passive Pressure and Coefficient of Friction assumes a safety factor of 1.5 (permanent conditions). 5. Equipment surcharges can typically be accounted for by increasing the effective height of the shoring wall by 2 feet. Since permanent concrete lagging (shotcrete or panels) is planned for the proposed shoring wall, no reduction should be applied to the active earth pressures to account for arching of the lagging between the piles. Active soil conditions assume that the wall is allowed to rotate or yield so the top of the wall moves an amount equal to or greater than about 0.001 to 0.002 times its height. GeoTest also recommends that a seismic surcharge pressure of 8H be included where H is the wall height in feet. The active soil condition is an equivalent fluid with a triangular distribution, acting over the pile and between the pile spacing on the exposed (or excavated) portion of the wall. Below the excavation, the active soil conditions are only acting over the diameter of the grouted pile section. The table above gives active pressures for a level or 2H: 1V backslope. Soldier piles must be designed with sufficiently stiff or rigid steel beams embedded and grouted into native soil to resist active soil pressure. GeoTest recommends that the upper 2 feet of passive soil pressure be neglected due to near -surface soil disturbance. The recommended passive 10