3A Public Hearing 2006 1204 - Laserfiche WebLink

Home

GEOTECNIA Project Number: 060805 2888 Darius Way, San Leandro October 27,2006 Page 6 We understand that no unsupported fills are planned at the site to raise the grades (other than retaining wall backfill as discussed below). If unsupported fills are planned in the future. we should be contacted to (1) provide criteria for sidehill filling, and (2) provide estimates of anticipated future differential settlements due to the weight of the new fill. The existing V-ditches, drain inlets, and subsurface drain line (connecting the drain inlets) shown on Plate 2 should be protected during construction. If any excavations (especially pier drilling) are planned within 3 feet of the subsurface drainpipe location. potholing would be required to accurately locate the pipe. If the pipe were damaged during construction, it should be repaired so that it continues to perfonn as designed. Seismic Design The site is within UBC Seismic Zone 4 and the subsurface profile at the site best approximates type Sc. To calculate total lateral seismic forces acting on the structures in accordance with the 1997 UBC, the following criteria should be used for design: a seismic zone factor (Z) of 0.4; a near-source acceleration factor, Na. of 1.5; a near-source velocity factor, Nv, of2.0; an acceleration seismic coefficient, Ca, of 0.60. and a velocity seismic coefficient, Cv, of 1.12 (ICBO, 1997). Site Preparation and Gradine: Clearing Areas to be graded or excavated should be cleared of topsoil, debris, vegetation, roots, and deleterious material, as applicable. The cleared materials should be removed from the site, although the organic materials may be re-used in landscaped areas. Backfill Materials The in-situ clay soils (both fill and native) are not suitable for reuse as backfill behind retaining walls, except for the upper 12 inches above backdrains as discussed below. Import backfill materials should have a PI of 12 or less, should have no particles or lumps greater than 4 inches in largest dimension. and should preferably be granular soils (sand, gravel, or sand/gravel mixtures). Import backfill materials should be approved by the geotechnical engineer prior to use. Backfill materials should be placed in level lifts not exceeding 8 inches in loose thickness. Each lift should be brought to at least the optimum moisture content, and compacted to at least 90 percent relative compaction, in accordance with the ASTM D 1557 test method. Relative compaction refers to the in-place dry density of a soil expressed as a percentage of the maximum dry density of the same material, as determined by ASTM D1557. If the backfill materials are compacted as recommended above, they should experience settlements less than 1 inch.