3400 RIVERFRONT BLVD Geotech Report 2022-10-25

S S S • 6.14.3 Wall Drainage and Backfill . The above design parameters have been provided assuming that drains will be installed behind the walls to prevent buildup of hydrostatic pressures. If a drainage system is not installed, then S our office should be contacted for revised design forces. S • Backfill material placed behind retaining walls and extending a horizontal distance of Y2H (where S H is the height of the retaining wall) should consist of imported granular material meeting the requirements described in the "Structural Fill" section of this report. Alternatively, the native soil S can be used as backfill material provided a minimum 2-foot-wide column of angular drain rock • wrapped in a drainage geotextile is placed against the wall and the native soil can be adequately S moisture conditioned for compaction. The rock column should extend from the perforated drainpipe or foundation drains to within approximately 1 foot of the ground surface. The • angular drain rock should have a maximum particle size of 1 inch, have less than 2 percent • passing the U.S. Standard No. 200 Sieve, have at least 2 mechanically fractured faces, and be free • of organics and other unsuitable material. • Perforated collector pipes should be placed at the base of the granular backfill behind the walls. S The pipe should be embedded in a minimum 2-foot-wide zone of angular drain rock wrapped in • a drainage geotextile fabric. The collector pipes should discharge at an appropriate location S away from the base of the wall. Unless measures are taken to prevent backflow into the wall's • drainage system, the discharge pipe should not be tied directly into stormwater drain systems. • Backfill should be placed and compacted as recommended for structural fill, with the exception • of backfill placed immediately adjacent to walls. Backfill adjacent to walls should be compacted • to a lesser standard to reduce the potential for compaction-induced earth pressures on the walls. Backfill located within a horizontal distance of 3 feet from the retaining walls should be S compacted to approximately 90 percent of the maximum dry density, as determined by • ASTM D 1557. Backfill placed within 3 feet of the wall should be compacted in lifts less than • 6 inches thick using hand-operated tamping equipment (such as a jumping jack or vibratory plate compactor). If flatwork (such as slabs, sidewalk, or pavement)will be placed adjacent to • the wall, we recommend that the upper 2 feet of fill be compacted to 95 percent of the • maximum dry density, as determined by ASTM D 1557. Settlement of up to 1 percent of the wall S height commonly occurs immediately adjacent to the wall as the wall rotates and develops active • lateral earth pressures. Consequently, we recommend that construction of flatwork adjacent to retaining walls be postponed at least four weeks after construction, unless survey data indicates S that settlement is complete prior to that time. S • 6.15 SEISMIC DESIGN PARAMETERS • Based on the results of the site investigations and our analysis, it is our opinion that the site contains liquefiable soil, which automatically results in the designation of seismic site class F and • the requirement to perform a site response analysis, according to Chapter 20 of ASCE 7 (ASCE, • 2010). However, there is an exception in Chapter 20 of ASCE 7 stating that structures with a • fundamental period of vibration less than 0.5 second do not need to be classified as seismic site • class F and do not require a site response analysis. We anticipate that the structures that will be built for this project will have fundamental periods of vibration less than 0.5 second, although this should be confirmed by the project structural engineer. As a result, it is our opinion that the • • • G EODESIGN? 21 Polygon-128-01:091615 S