4920 EVERGREEN WAY STAPLES Geotech Report 2022-10-25

Geotechnical Engineering Report IIrracon Staples Rockery Failure Everett,Washington March 8, 2019 Terracon Project No. 81175122 Equivalent Maximum Earth Pressure Surcharge Seismic Earth Fluid Density Apparent Earth Conditions Pressure, S(psf) Pressure, E (psf) (pcf) Pressure, P (psf) Active (Ka) = 0.33 --- (40)H 80 (17.5)H Passive(Kp)= 3.1 B = 400 --- -- Applicable conditions to the above include: For active earth pressure, wall must rotate about base, with top lateral movements of about 0.002 H to 0.004 H, where H is wall height For passive earth pressure to develop, wall must move horizontally to mobilize resistance Uniform pressures for surcharge and seismic for the full wall height In-situ retained soil weight of 120 pcf Structural fill compacted to 95 percent of modified Proctor maximum dry density Loading from heavy compaction equipment not included No hydrostatic pressures acting on wall No factor of safety, reduction factors, or load resistance factors are applied Ignore passive pressure in frost zone (assumed to be up to 2 feet) Backfill placed against structures should consist of granular soil as described in Section 4.2.3. For these values to be valid, the granular backfill must extend out and up from the base of the wall at an angle of at least 45 and 60 degrees from vertical for the active and passive cases, respectively. 4.5 Retaining Walls The following sections present design and construction recommendations for soldier pile/tieback walls. Terracon's scope of services includes preparation of design plans and specifications for the recommended soldier pile / tieback wall and this geotechnical report will form the basis of design. 4.5.1 Soldier Piles Soldier piles are typically set in drilled holes and backfilled with lean or structural concrete. Soldier pile installation may involve casing the holes and/or drilling with a mud slurry to maintain an open hole to prevent caving or cut off groundwater seepage. Passive earth pressures act on the embedded portion of the soldier piles and resist horizontal loads on the retaining system. The passive earth pressure will act over three diameters of the concreted soldier pile section or the pile spacing, whichever is less. The active earth pressures act over the concreted pile diameter below the base of the excavation. Vertical capacity of the soldier piles may be provided by a combination of end bearing and side friction below the base of the excavation. The piles can be designed for an allowable end bearing Responsive • Resourceful • Reliable 11