5720 EAST DR 2018-01-02 MF Import

Geotechnicel Engineering Report Parcel 00471700002401- 57XX East Drive Everett, Washington December 12, 2009 RMI File No. 53409 Page 10 resistance acting on the below -grade portion of the foundation. Recommendations for frictional and passive resistance to lateral loads are presented in the Foundations subsection of this report. Permanent drainage systems should be installed for retaining walls (and subsurface walls). We recommend that these drainage systems consist of an 18-inch wide zone of clean (less than 3 percent fines), free -draining granular material placed along the back of the wall. Pea gravel is an acceptable drain material, or drainage composite may be used instead. We recommend that we be retained to evaluate the proposed wall drain backfill material for its suitability. The granular material should be placed up the back of the wall to within 1 foot of the ground surface. The top I -foot should be a layer of compacted, low -permeability soil to limit surface water infiltration and should be separated from the underlying free -draining material by a layer of plastic sheeting or building paper. A rigid perforated or slotted PVC drainpipe, having a minimum diameter of 4 inches, should be embedded in pea gravel or some other free -draining material and wrapped in a non -woven filter fabric such as Mirafi 140NSL at the base of the wall along its entire length. This drainpipe should discharge into tightlines leading to an appropriate collection and discharge point. Surface water drains and roof drains should not be connected to wall or footing drains until there is at least I foot of elevation difference below the footing drains. All wall backfill should be well compacted as outlined in the Structural Fill subsection of this report. Care should be taken to prevent the buildup of excess lateral soil pressures, due to overcompaclion of the wall backfill. This can be accomplished by placing wall backfill in 8-inch thick loose lifts and compacting it with small hand -operated compactors within a distance behind the wall equal to at least one-half the height of the wall. Closure If the recommendations in this report are implemented, the project should not be adversely affected by the stability of the slopes on the site nor should the project affect the stability of the slopes. This report is issued with the understanding that it is the responsibility of the owner or his representative to ensure that the information and recommendations contained in this report are called to the attention of all concerned parties and incorporated into the plans and that the necessary steps are taken to see that the contractors or subcontractors carry out such recommendations in the field. RMI ASSOCIATES LLC 1I 1