11831 AIRPORT RD WHOLE SITE FILE Geotech Report 2022-10-25

Lateral Resistance The lateral earth pressures on shallow foundations may also be resisted by friction on the base of the footings. The ultimate frictional resistance presented in Table 6 assumes that the foundation soils consist of medium dense sand or gravel. If unsuitable soils(loose fill, colluvium or disturbed glacially consolidated soils)are exposed at the footingsubgrade these materials should be recompacted or removed and replaced as described in the "Subgrade Preparation"section of this report. The passive resistance may be computed using the unfactored (nominal) passive pressures shown in Table 5. The appropriate resistance factors for passive resistance and sliding resistance are shown in Table 6. TABLE 6. LRFD REDUCTION FACTORS FOR PASSIVE AND SHEAR RESISTANCE TO SLIDING Limit State Passive Resistance to Sliding Shear Resistance to Sliding Strength 0.5 0.8 Service 1.0 1.0 Extreme 0.9 0.9 All CIP retaining walls should be designed in accordance with Section D of the WSDOT Standard Plans for concrete cantilever retaining walls. Wall Drainage The recommended equivalent fluid densities presented in Table 5 assume a free-draining condition behind the wall. Permanent drainage systems should be provided to collect water and prevent the buildup of hydrostatic pressure against the wall as outlined in the previous wall drainage section for the station walls. Wall 2 Soldier Pile Wall We understand wall 2 might also be designed and built as a soldier pile wall. Soldier pile walls consist of steel beams that are concreted into drilled vertical holes located along the wall alignment, typically 6 to 10 feet on center.Temporary timber lagging is used between the piles along with a permanent CIP concrete facing, or permanent concrete lagging can be used. Cantilever soldier pile walls can be used up to about 15 feet in height. For taller walls, tiebacks consisting of steel strand drilled anchors can be installed for additional lateral capacity. At this time, we anticipate that tiebacks will not be required. Design Recommendations The design earth pressures for soldier pile walls should be developed using Table 5 and as shown in the Earth Pressure Diagram, Figure 3.Traffic surcharge loads and other surcharge loads,such as foundations, construction equipment, or construction staging should also be considered on a case-by-case basis, if applicable. The embedded portion of the soldier piles must be at least 2 feet in diameter and extend a minimum distance of 10 feet below the base of the wall to resist"kick-out."The axial capacity of the soldier pile must resist the downward component of any vertical loads, as appropriate. The axial capacities of soldier pile shafts can be evaluated using an ultimate end-bearing value of 35 kips per square foot (ksf) for piles embedded in very dense glacially consolidated soils. GEOENGINEERS. April 14,2017 Page 16 File No.2095-032-00