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Subsurface EcpJoration, Grologic Namrd, and <br />Brl��cdcre L.ots Ensr Preliminnry Geoterhniral Engineering Report <br />E� rrerr R'nshingmn P�eliminary Design Recommendntions <br />Portions of the namral sediments contain a high percentage of fine-grained material that makes <br />!hcm moiswre-sensitive and subject to dismrbance when wet. The contractor must use care <br />during site preparation and excavation operations so that the undcrlying soils are not softened. <br />If disturbance occurs, the softened soils should be removed and the area brought to grade with <br />structural fill. <br />Consideration should be given to protecting access and staging areas with an appropriate <br />section of crushed rock nr asphalt veated base (ATB). If crushed rock is considered for the <br />access and staging areas, it should 'ue underlain by engineering stabilization fabric to reduce <br />the potential of fine-grained materials pumping up through the rock during wet weather and <br />turning the area to mud. The fabric will also aid in supporting construction equipment, thus <br />reducing the amount of crushed rock required. ��'e recommend Ihat at least 10 inch�:s of rock <br />be placed over the fabric. <br />]0.0 STRUCI'UR:'�L I�ILI. <br />Placement of strucwral fill may bc reyuired to establish c'esired grades in some areas. .411 <br />ref;rences to structural fill in this repurt refer to subgrade preparation, fill type, pl2cement, <br />�nd compaction of materials as discussed in this sectian. If a perc..ntage of comE�action is <br />specified under another section of this report, the value given iu that section should be used. <br />After stripping, planned exca��ation, and any tequired overexcavation have been performed to <br />the satisfaction of the geotechnical engineer/engineering geologist, tne upper 12 inches of <br />exposed ground should he recornpacted to at least 90 percent of the mudified Procto� maximu:n <br />densit� using ASTP.t:D 1557 as the standard. If the subgrade contains too much moisture, <br />adrquate recomraction may he difficult cr impossible to obtain and should probably not be <br />attcmpted. In lieu nf re�ompaction. the a:ea m receive fil: should be blanketed �eith u•ashed <br />rock or quarry spalls to act as a capillary break hetwcen the new fill and the wet subgrade. <br />Wherc the exposed ground remains soft and further overeacavation is impractical, placement <br />nf �n engineering stabilization fabric may be necessary to prevent contamination of the free- <br />draining laycr b}� silt migration from beloµ. <br />.4ftrr recompaction of the exposed ground is tested and approved, or a free-draining rock <br />cuurse is laid, structural fill may be placed to attain desired grades. Strucmral fill is defined as <br />non-organic soil, acceptable to the geotechnical engineer, placed in maximum S-inch loose lifts <br />N ith cach lift being compacred to at least 95 percent of the modified Procter maximum densiry <br />using ASTM:D 1557 as the standard The on-site namral sand sediments are generally suitable <br />for usc as strucwral fill, but portious of these sediments contain substantial quantities of silt <br />and are considereA highh moisture-sensitive. If the moisture centents of these sediments are <br />cl�� atrd at the time of construction, moisture conditioning may be required prior to their use as <br />uruciur;il fill. Such nioiuure ec�uditioning could consist of spreading out and aerating the soil <br />.qlnn�l; 5, �rM�J .ISSOGATED E.1R7NSClENCES, INC. <br />r:,�,., ,�����;,�� �,,,,..:,:�,�„��.� „�� �,�:�. Page ll <br />