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Geotechnical Engineering Study Page 33 <br />00-226T Three Story Addition - 500 Laurei Street, Everett <br />January 31, 2001 <br />fa�ing downwards. The drain pipe should be becided on, su�rounded by, and <br />covered with, a clean, free-draining grani�.�r back.fill, such a� oea gravel or a <br />washed rock, and should have sufficient gradient to initiate gra�- / flow. The drain <br />pipe must be tightlined to discharge under control into a pErma. �ent system, such <br />as a nearby storm drain catch basin or manhole structure. <br />Any "buried" foundation stern wa�! (or any retaining wall) should also be provided <br />with a drainage system similar to that described above for conventional footings. <br />Ttie drainage materials should extend up the full height of the buried portion of the <br />wall to help rapidly dissipate any collected seepage and avoid the potential for <br />hydrostatic pressure buildup. We also recommerd tnat the free-draining material <br />meet the requirement:� of the 1996 WSDOT Standard Specifications for Rcad, <br />Bridge, and Municipal Construction, Section 9-03.12(2) Gravel Backfill for Walls, as <br />follows. <br />Material and Percentage <br />Sieve Size of Materiai <br />Passing <br />4 inch 100 <br />1 /4 inch 25 - 70 <br />#200 mesh 5 max. <br />l]ust Ratio 2/3 max. <br />Sand 60 min. <br />E uivalent <br />V�✓e suggesk subsurface drainline �ocations, if appropriate, be established during <br />I the Qarthwork phase of the project by our representa±ive when seepage areas and <br />conditions may be more clearly defined. All areas to rece���e these drainlines <br />I should be ab:;erved by tne geotechnical engineer. Where the imm�gration of fines <br />from the native soil into the above-referen��e+d drainage material may compromise <br />tfie drain, tha gravei backfill stiould be proler.ted by a geotextiRe filter cloth. <br />� <br />I <br />�`�'J <br />