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July 21, 2014 <br />Two Single-Family residences <br />L&A Job No. 14-065 <br />Page 14 <br />loading. The wall should be designed for a factor of safety of at least 1.15 against sliding <br />failure and 1.2 against overturning failure under seismic loading. <br />A drain line consisting of perforated, rigid PVC, drain pipes, at least 4 inches in diameter, <br />should be installed at a few inches below bottorri of retaining wall to intercept and drain <br />away groundwater flowing towards the wall. The drain line should have sufficient slope <br />(0.5 percent minunum) to generate flow by gravity, and water collected in the drain line <br />should be tightlined to discharge into a storm sewer or suitable stormwater disposal <br />faciiities. The drain line should be wrapped in a layer of non-woven filter fabric, such as <br />, ,, ,., i Tr ,.,�; � , , .,, , � „ , �, ,>� ,�T . ��r�al , �a�d �;o��1PtPlv ernb�dded ir� clean washed <br />. �., �, ��1 <br />, r _l,. ,, �- � � , <br />gra�el or cr�shed rock to within about 1� inc���s oi �he ��ish g�ad�. �'� v�3��cal ��a�i�ag�, <br />blanket at least 12 inches thick, consisting of clean, 3/4 to 1-1/2-inch, washed gravel or <br />crushed rocl�, should be placed against the wall. Altematively, a vertical drain mat, such <br />as Miradrai�a 6000 by Mirafi Inc., or approved equal, may be placed against the walls as <br />the vertical drainage blanket. The vertical drainage blanket or drain mat should be <br />hydraulically connected to the drain line at the base af the retaining wall. <br />Soldier Pile Wall <br />A cantilever soldier pile retaining wall may also be constructed along the toe of the <br />hillside as a.� option to stabilize tl�e hillside. A soldier pile wall is constructed by drilling <br />holes into the ground, inserting steel beams in the hoies, and filling the holes with <br />structural concrete. Timber boards, treated for outdoor and soil contact use, are placed <br />against cut �ank between soldier piles. The saldier pile wall should be designed for an <br />active soil pressure of 35 pcf EFD (equivalent fluid density) plus 0.75�3 pcf, where � is <br />L�U & ASSOCIATES, INC. <br />