1010 N BROADWAY EVCC 2018-01-01 MF Import

PROPOSED LIBERTY HALL,EVERETT COMMUNITY COLLEGE =s; Everett,Washington Design Parameters Lateral earth pressures for design of below-grade walls and retaining structures should be evaluated using an equivalent fluid density of 35 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. Surcharge effects should be included as appropriate. Below-grade walls for buildings should also include seismic earth pressures. Seismic earth pressures should be determined using a rectangular distribution of 7H in psf, where H is the wall height. If vehicles can approach the tops of exterior walls to within 1/2 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. Other surcharge loads, such as from foundations, construction equipment, or construction staging areas, should be considered on a case-by-case basis as shown on Figure 5. Positive drainage should be provided behind below-grade walls and retaining structures as discussed below. These recommendations are based on the assumption that all retaining walls will be provided with adequate drainage. The values for soil bearing, frictional resistance and passive resistance presented above for foundation design are applicable to retaining wall design. Walls located in level ground areas should be founded ata depth of 18 inches below the adjacent grade. • Wall Drainage To reduce the potential for hydrostatic water pressure buildup behind the retaining walls, we recommend that the walls be provided with adequate drainage, as shown in Figure 4. Wall drainage can be achieved by using free draining wall drainage material with perforated pipes to discharge the collected water. Wall drainage material may consist of washed 3/8-inch to No.8 pea gravel per WSDOT 9.03.1(4)C, AASHTO Grading No.8,or clean gravel (gravel backfill for drains per WSDOT Standard Specification Section 9-03.12(4)) surrounded with a non-woven geotextile fabric such as Mirafi 14ON (or approved equivalent). The zone of wall drainage material should be 2 feet wide and should extend from the base of the wall to within 2 feet of the ground surface. The wall drainage material should be covered with 2 feet of less permeable material, such as the on-site silty sand that is properly moisture conditioned and compacted. Page 18 June 10,2010 GeoEngineers,Inc. FlIeNo.5836.010.OD