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Project No. 1281 <br /> I 1 Oc�01 <br /> placed on these soils. Parking lot pavements may be similarly supported. £xcavations <br /> for detention pond cons�truction will extend into the weathered and unweathe.red till soils. <br /> I3ecause a perched, intertlow condition was not observed 'm B-2, we anticipate that <br /> groundwater seepage will not signi6cantly impact pond water levels. <br /> Loose, organic soils were noted to a depth of 5 '/z feet m B-3. These soils will not be <br /> suitable for suppori of the southeaslern pavements and detention vault. Accordingly, <br /> excavalion and removal of these soils followed by replacement with structural fill may be <br /> reGuired during�ite grading in this location. <br /> '1'he following sections provide detailed recommendations regarding the above issues and <br /> other geotechnical design considerations. These recommendations should be <br /> incorporated into the final design drawings and construction specifications for the project. <br /> 6.2 Site ('Iearina :�nd Suberade Prenara6on <br /> Prior to earihwork operations, the site's demolition debris should be removed and the <br /> ground cleared of all deleteriou� materials, including vegetation and organic rich soil <br /> ancUor buricd wood debris. Upon completion of the site demolition and dearing, the <br /> groimd snrface should be raked clean. Deleterious materials shou�d be removed and <br /> Jisposed ofproperly. <br /> The following are recommendations for over-excavation and subgraJe preparation: <br /> I. Wc recommend remo�hng all existing asphalt concrete in areas of new <br /> const:uction. Existing asphalt may be recycled for on-site use as structural fil! by <br /> pulverizing or grinding it into gravel-sized (less than 3 mches) particles, mixing il <br /> with the underlying subgraJe, and compacting it as describeJ below. <br /> 2. '1'he subgrade soil should be compacted to a dense and unyielding condition and <br /> then proof-rolled with heavy construction equipment such as a large vt'lrratory <br /> roller or a fully loaded Jump truck. Successive passes of the roller or dump trucic <br /> should be spaceJ to provide complete coverage of the subgrade. Proof-rolling <br /> should be perf'ormed under the full-time observation of a representative of <br /> Milbor-Pita & Associates (MPA). If the subgrade is wet, saturated, or frozen, <br /> proof rolling should not be performed. Under this circumstance, the geotechnical <br /> observer using a sYeel peobe should evaluate subgrade conditions. <br /> 3. Any areas exhibiting significant delleclion, pumping, ancllor rutting during the <br /> proof-rolling/probing process should be over-excavated and replaced with <br /> compacted structural fill in accordance with the following section. The over- <br /> cxcavation process shotJd be observed by NIPA. <br /> 4. �or new construction in the area of the existing northeastem detention pond, we <br /> recommenc! draining the pond and removing the accuinulated soR muck in the <br /> pond bottmn prior to retaining wall and detention vault construction, and the <br /> placement of structural fill. Where over-excavation is requ'ved, and wet <br /> condilions exist in the excavation, rctaining wall and detention vault subgades <br /> graJes should be restored �v�th compacted crushed rock. <br /> Geotahnical and T�mnel Fsgineers �\ <br /> 3U80 125°i Avc NE I'hme(425)869-5778 v <br /> [3ellewc,WA9EiW5 PageS Fa+o (435)861-0677 <br />