SR0085267_SSNL - Laserfiche WebLink

Home Browse Search

Phelan Development Holly Master Plan - Buildings H & 1 15188.000.006 Geotechnical Exploration seismic lateral earth pressure corresponding to an equivalent fluid pressure of 30 pcf for a yielding wall design. When considering seismic earth pressures for retaining walls, the recommended seismic earth pressure increment should be added to the active earth pressures provided above. Appropriate surcharge loads from buildings, hardscape, and vehicles should be incorporated when the surcharge loading is situated above a 1:1 (horizontal:vertical) line of projection extending up the rear base edge of the bottom of the footing. A uniform horizontal surcharge load of 50 percent of the vertical surcharge load should be assumed to act over the height of the wall. If adequate drainage is not provided, we recommend that an additional equivalent fluid pressure of 40 pcf be added to the values recommended above for both restrained and unrestrained walls. Damp-proofing of the walls should be included in areas where wall moisture would be problematic. Passive pressures acting on foundations may be assumed as 300 pounds per cubic foot (pcf) provided that the area in front of the retaining wall is level for a distance of at least 10 feet or three times the depth of foundation, whichever is greater. The friction factor for sliding resistance may be assumed as 0.25. The upper 1 foot of soil should be excluded from passive pressure computations unless it is confined by pavement or a concrete slab. Passive pressures should be reduced by 1/2 if used in combination with sliding friction. 8.2 RETAINING WALL DRAINAGE Construct either graded rock drains or geosynthetic drainage composites behind the retaining walls to reduce hydrostatic lateral forces. For rock drain construction, we recommend two types of rock drain alternatives. 1. A minimum 12-inch-thick layer of Class 2 Permeable Filter Material (Caltrans Specification 68-2.02F) placed directly behind the wall, or 2. A minimum 12-inch-thick layer of washed, crushed rock with 100 percent passing the %-inch sieve and less than 5 percent passing the No. 4 sieve. Envelop rock in a minimum 6-ounce, nonwoven geotextile filter fabric. For both types of rock drains: 1. Place the rock drain directly behind the walls of the structure. 2. Extend rock drains from the wall base to within 12 inches of the top of the wall. 3. Place a minimum of 4-inch-diameter perforated pipe (glued joints and end caps) at the base of the wall, inside the rock drain and fabric, with perforations placed down. 4. Place pipe at a gradient at least 1 percent to direct water away from the wall by gravity to a drainage facility. ENGEO should review and approve geosynthetic composite drainage systems prior to use. 8.3 BACKFILL Backfill behind retaining walls should be placed and compacted in accordance with Earthwork Recommendations contained in this report. Use light compaction equipment within 5 feet of the —NGE0 Page 120 December 13, 2021 Expect Excellence