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%111 ✓ <br /> y, Section 5.0 <br /> Engineering Analyses and Recommendations <br /> 5.4.2 Lateral Earth Pressures <br /> Based on the subsurface conditions encountered on the two borings,estimated lateral <br /> �- pressures acting on the shoring wall were calculated and are presented on Figure 3. <br /> The lateral pressures for the proposed permanent wall are presented on Figure 4, <br /> assuming that imported fill and relatively light compaction equipment due to spatial <br /> • constraints would be used. For the seismic pressures, the project site is located in <br /> Zone 3 according to the 1997 Uniform Building Code (UBC). The site peak ground <br /> acceleration(PGA) is about 0.368 for a recurrence interval of 475 years and <br /> considering the subsurface conditions. Different surcharge loads are presented on <br /> Figure 5. <br /> 5.4.3 Backfill <br /> We believe that most on the onsite soils are not suitable for backfill. Resistivity values <br /> less than 2,000 ohm-cm were measured in the soil samples obtained from the two <br /> borings. Therefore, these soils are considered highly corrosive. Moreover, most of <br /> these soils are wet, soft clay,which are typically difficult to compact properly. If the <br /> wet,soft clay would be used as backfill,then long-tem settlement of the ground <br /> surface might occur. The settlement of the ground surface may also cause settlement <br /> of the wet pit due to downdrag forces. <br /> We recommend using imported fill consisting of clean,free-draining sand and gravel <br /> containing less than 12 percent fines (silt and clay sized particles) based on the <br /> l fraction passing the 3/4-inch sieve. Onsite soils meeting these requirements can be <br /> _ used for backfill. The backfill materials should be placed in lifts,with each should not <br /> exceed 12 inches in loose thickness. The backfill materials should be compacted to at <br /> fa- least 90 percent of the maximum modified dry density determined in the laboratory <br /> using ASTM Method D1557. <br /> 5.5 Stability of Pump Station and Wet Pit <br /> We evaluated the sliding and uplift stability of the pump station and wet pit during <br /> .im. construction. The pump station has a factor of safety of over 2.0 against uplift during <br /> construction. The wet pit has a factor of safety of 1.4 against uplift assuming the walls <br /> of the wet pit are 12 inches thick. For sliding stability, the pump station has a factor of <br /> �., safety of over 1.2 against sliding provided that the pump station including the east <br /> extension (no excavation around the east extension)will resist the driving lateral force <br /> as one rigid structure. In other words,the lateral driving force acting on the 24-foot- <br /> long north wall of the pump would be resisted partially by the east extension of the <br /> pump station. For the wet pit structure,excavation limits should encompass the wet <br /> pit entirely or the wet pit should be braced to avoid sliding instability. <br /> 46. CDM cam & <br /> 5-4 <br /> } p\2500529248.GE0-7LRepoFtBrookside Pump StOon doc <br /> Aw <br />