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-1 K L E I N F E L D E R Shored Eicai arz ons In areas where existing site features interfere with temporary sloped excavations, we anticipate trench and/or jacking pit excavations will be shored As indicated earlier, the soils encountered during our field exploration consisted of stiff to hard clays and silts with interbedded layers and strata of loose to medium-dense, potentially caving or sloughing sands Accordingly, the Contractor should exercise care during excavations at the site y Where ` clean" sands are encountered, excavations will require continuous or solid-type shoring (e g , interlocking sheet piles or similar system) during excavation Conventional shonng, such as intermittent trench jacks may not adequately q ely support excavation walls Furthermore, the "clean sands may not stand vertically long enough to move shoring into place following excavation Shoring should be removed as backfilling progresses Shoring should be designed to resist the earth pressure exerted by the retained soil plus any additional lateral force due to surcharge loading, i e , construction equipment, foundations, roadways, etc , at or near the shonng The following equivalent fluid earth pressures are recommended assuming a maximum shoring height of 30 feet, a level ground surface, an effective soil uiut weight of 120 pcf, and a fully drained soil condition Earth Pressure Earth Pressure Lateral Earth Condition Coefficient Pressure ( ef) Active 035 39 iAt-Rest 0 52 58 Passive 288 315 Lateral soil pressure diagrams for braced shoring in cohesive clays or silts and cohesionless sands and gravel are presented on Plate 2 The lateral pressure diagrams assume temporary excavations are properly dewatered and do not account for surcharge loads or vibration due to stockpiled soils, construction equipment, building loads, or vehicle traffic The Contractor should consult with an experienced consultant to design the required shoring systems prior to earthwork activities Const-uctiorr Dewatering i We anticipate the bottom of the trench will be less than 25 feet below the existing site grade this corresponds to a depth of about 181,', feet below the highest groundwater level encountered during our field investigation During construction of the trench, soils exposed below the groundwater level could become unstable or even "quick ' due to upward seepage forces loosing their ability to support foundations and maintain stabile trench slopes Therefore, we anticipate that dewatering will be necessary to permit stable construction The groundwater should be lowered and continuously maintained at least 3 feet below the bottom of the proposed excavation until the structure and backfill weight is adequate to provide uplift resistance and backfill is complete at least 3 feet above the normal stabilized water level 13629 001,2002R369 -�prll 19 200 "J 2002 Kleinfelder Inc Page 6 of 16