3815 SHORE AVE 2020-05-20 - Laserfiche WebLink

Geologically Hazardous Areas; Geotechnical Letter Kennedy Single Family Residence 3815 Shore Avenue March 23, 2018 RN File No. 3279-001A Page 8 foundation excavation prior to placing concrete. Loose or disturbed soil was observed in the explorations to depths of approximately 4 feet. For foundations constructed as outlined above,we recommend an allowable design bearing pressure of 2,500 pounds per square foot (pal) be used for the footing design, IBC guidelines should be followed when considering short-term transitory wind or seismic loads. Potential foundation Settlement using the recommended allowable bearing pressure is estimated to be less than 1-inch total and 1/2-inch differential between footings or across a distance of about 30 feet Higher soil bearing values may be appropriate with wider footings. These higher values can be determined after a review of a specific design. Lateral Loads The lateral earth pressure acting on retaining walls is dependent on the nature and density of the soil behind the wall,the amount of lateral wall movement, which can occur as backfill is placed, and the inclination of the backfill. Walls that are free to yield at least one-thousandth of the height of the wall are in an "active" condition. Walls restrained from movement by stiffness or bracing are in an "at-rest" condition.Active earth pressure and at-rest earth pressure can be calculated based on equivalent fluid density. Equivalent fluid densities for active and at-rest earth pressure of 35 pounds per cubic foot (pcf) and 55 pcf, respectively, may be used for design for a level backslope. These values assume that the on-site soils or imported granular fill are used for backfill,and that the wall backfill is drained. The preceding values do not include the effects of surcharges, such as due to foundation loads or ether surface loads. Surcharge effects should be considered where appropriate. Seismic lateral loads are a function of the site location, soil strength parameters and the peak horizontal ground acceleration (PGA) fora given return period. We used the,US Geological Survey program "U.S. Seismic Design Maps Web Application" to compute the PGA for the site. The design maps summary report for the 2012/1518C is included in this report as Appendix A. The above drained active value should be increased by a uniform pressure of 8.5H, when considering seismic conditions. H represents the wall height.. The above lateral pressures may be resisted by friction at the base of the wall and passive resistance against the foundation.A coefficient of friction of 0.5 may be used to determine the. base friction in the native glacial soils. An equivalent fluid density of 200 pcf may be used for passive resistance design. To achieve this value of passive pressure, the foundations should be poured "neat" against the native dense soils, or compacted fill should be used as backfill against the front of the footing, and the soil in front of the wall should extend a horizontal distance at least equal to three times the foundation depth. A resistance factor of 0.67 has been applied to the passive pressure to account for required movements to generate these pressures. The friction coefficient does not include a factor of safety. All wall backfill should be well compacted. Care should be taken to prevent the buildup of excess lateral soil pressures due to overcompaction of the wall backfill. Robinson Noble, Inc.