4704 HARBOR LN 2018-01-02 MF Import

' Geotechnical Engineering Evaluation .Anderson Landslide Repairs ' 4704 Harbor lane Everett, Washington September 15, 2009 NGA pile No. 816909 Page 18 The wall should be lagged using pressure -treated timber or concrete panels. Adequate gaps should be maintained between the lagging elements to allow water flow through the face of the wall. Also, all wall backfill should consist of 2-inch clean drain rock. It is imperative that water not be allowed to pool behind the wall, therefore extreme care should be taken not to contaminate the drain rock with silt or organics. In wet conditions, it might be necessary to use a filter fabric along the back of the drainage layer. Tie -Backs General: Tic -backs will be necessary for this wall. The contractor or the wall designer should submit for review working drawings showing their proposed method of tic -back support. The drawings shall include lists of materials to be used, sequence of operations and sufficient number details and notes to clearly illustrate the scope of work. Double corrosion protection for the anchor strands/bars shall be detailed on the drawings. We recommend that five percent of the anchors, but not less than two, be treated as performance anchors and be tested to a minimum of 200 percent of the design loads. The soil creep characteristics would be evaluated in these tests. No -Load Zone: The anchor portion of all tie -backs must be located a sufficient distance behind the retained face, to develop resistance within a stable soil mass. We recommend the anchorage be obtained behind an assumed no-load zone. The no-load zone was estimated from our stability analyses and should be a minina nt of 20 feet wide. We expect that competent sands and silts will exist beyond the no-load zone. Ilowcvcr, we do not have subsurface data at potential anchor locations. We recommend that we monitor soil conditions during anchor installation in order to evaluate adequate penetration into these soils. The tic -backs will be installed at an approximate inclination of roughly 15 degrees below horizontal. However, this inclination may need to be adjusted in the vicinity of the existing sw�nintiug pool. The anchor portion of the tic -back within the no-load zone should be immediatc!y backfilled. The sole purpose of the backfill is to prevent possible collapse of the holes, loss of ground and surface subsidence. We recommend that the backfill consist of sand, gravel or a non -cohesive mixture. A sand cement grout should be utilized only if an acceptable form of bond breaker (such as plastic sheathing) is applied to the NELSON GEOTECHNICAL ASSOCIATES, INC. -1y