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

An allowable soil bearing value of 2,000 psf may be used for footings supported as described above. The allowable soil bearing value applies to the total of dead and long-term live loads and may be increased by up to one-third for wind or seismic loads. We estimate that new wall footings designed as recommended above could experience between 1h and 3/4 inch of post-construction settlement. Lateral earth pressures for design of retaining structures should be evaluated using an equivalent fluid density of 35 pounds per cubic foot(pcf)provided that the walls will not be restrained against rotation when backfill is placed. If the walls will be restrained from rotation, we recommend using an equivalent fluid density of 55 pcf. Walls are assumed to be restrained if top movement during backfilling is less than H/1000, where H is the wall height. These lateral soil pressures assume that the ground surface behind the wall is horizontal. For unrestrained walls with backfill sloping up at 2H:1V, the design lateral earth pressure should be increased to 55 pcf, while restrained walls with a 2H:1V sloping backfill should be designed using an equivalent fluid density of 75 pcf.These lateral soil pressures do not include the effects of surcharges such as floor loads,traffic loads or other surface loading. If vehicles can approach the tops of exterior walls to within one-half the height of the wall,a traffic surcharge should be added to the wall pressure. For car parking areas,the traffic surcharge can be approximated by the equivalent weight of an additional 1 foot of soil backfill (125 psf) behind the wall. For delivery truck parking areas and access driveway areas, the traffic surcharge can be approximated by the equivalent weight of an additional 2 feet(250 psf)of soil backfill behind the wall. Lateral loads may be resisted by friction on the base of footings and foundation elements and passive resistance on the sides. Frictional resistance may be determined using 0.4 for the coefficient of base friction. Passive resistance may be determined using an equivalent fluid density of 300 pcf, assuming that the soils against the footings for a distance of twice the footing depth consist of compacted structural fill or medium dense to dense on site soils. Where a 2H:1V slope is present in front of the wall, or loose fill is present in front of the footing,the passive resistance should be reduced to 150 pcf.The above coefficient of friction and passive equivalent fluid density values include a factor of safety of about 1.5. These design parameters are based on the assumption that adequate drainage will be provided behind retaining structures as discussed below. Wall Drainage The recommended equivalent fluid density assumes 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. We recommend that the drainage system consist of a minimum 2-foot-wide zone of free-draining backfill against the back of the wall.The free-draining backfill should consist of:(1)pea gravel or (2) sand and gravel containing no more than 3 percent passing the U.S. No. 200 sieve based on the 3/4-inch fraction. In addition, a perforated drainpipe having a minimum diameter of 4 inches should be placed in the granular fill at the base of walls for the entire length. The drainpipe should consist of rigid polyvinyl chloride (PVC) or ADS N-12, not the flexible ADS variety.The drainpipe should be sloped to drain by gravity and routed to a suitable discharge point so that water discharged from the pipe does not cause erosion. Alternatively, weep holes can be used if the discharge of water will not impact any structure or landscaping in front of the wall. GEOENGINEER_ April 14,2017 Page 13 File No.2095-032-00