1303 W MUKILTEO BLVD 2016-01-01 MF Import

L� � L_' � Report ShoR Piat May 4, 1990 Page 5 The on site soils aze very susceptible to erosion. Any exposed soils should be planted with a suitable vegetation cover. This c�ver should be protected from surface water as nee9ed by suaw, jute netting or some other means until the vegetation is established. Embankments of loose on sitr soils should not be constructed steeper than a 4:1 (H:�. � 'll�e alternative to cut slopes would be to use a shoring system for temporary excsvation suppott. Shoring should be designed basad cn the anticipated cuts az�d sPec�fic design of the structure. � � � LI � � � LJ 'L� J � � L�'J � � SEI'AIIV[NG WALLS The lateral pressure acting on retaining walls is dependent on the nature and density of the soil behind the wall, the amount of lateral wall movement which can occur as backfill is Piaced; and the incliaation of the backfill. For walls that arc free to yield ac the top at least one thousandth of the heig6t of the wall, soil pressures will be less than if movement is limited by such faccors as wall stiffness or bracing. I recommend that yielding walls supporting horizontal bacl�fill be designed using an equivalent fluid density of 30 pounds per cubic foot (pc�, while nonyielding walls be designed using an equivalent fluid density of 50 pcf. 11�e above-recommendad lataal s°il pressures d° °°t u►clude the effecs of surcharges such as traffic loads or other surface loads. Surcherge effects should be considaed, if 3ppropriate. 'It�e above Iateral pressures may be resisted by friction at the base of the wall and passive pressure against the foundation. A coefficient of friction .' 0.5 should be used to determine the bau friction. I recommeed asin8 an e4�rvalent fluid pressure of 350 pcf for passive presswe desiga• An appropriate safay faaor should be applied to the above frictional coefficient and passive pressure values. All bac -lfill for subgrade walls should be compacted to between 90 and 92 Perce"t of the maximum dry density determi�ed �n accordance with ASTM D-1557. Caze should be talcen to prevent the buildup of excess lateral soil pressures due to overcompaccion of the backfill behind the wall. This can be accomplished by placing the backtill located within 18 to 24 inches of the wall in lifts not exceeding 8 inches in loose thickness and compacting this zone with hand operated vibrazing plate compactors. COUVRETTE GEO'fECfWICAL ENGINEERING