2702 59TH ST SW 2024-07-05 - Laserfiche WebLink

Geotechnical Engineering Evaluation Miller Property Slope Stabilization Everett, Washington NGA File No. 1333322 July 1, 2022 Page 13 The above loads should be applied on the full center -to -center pile spacing above the base of the exposed portion of the wall. A 50 percent reduction of this value can be applied for the purpose of designing the wall lagging. The active pressure could be partially resisted by passive resistance acting on the below -grade portion of the piles. The passive resistance could be calculated based on a 150 pcf equivalent fluid density acting on two effective pile diameters below the base of the exposed portion of the wall. This value incorporates a factor of safety of 2.0. The upper four feet of soil should be neglected when calculating the passive resistance. We recommend that most of the lateral loads be resisted by drilled and grouted tieback anchors. Shoring Wall Installation: The shoring wall should be installed by a shoring contractor experienced with this type of system. Although we anticipate that an open -hole drilling method will be adequate for installing the soldier piles in the on -site soils, the shoring contractor should plan on casing the majority of the holes as sloughing and/or water seepage will likely be encountered in the upper wet, loose fill. It might be prudent to perform one or more "test" holes to confirm installation conditions prior to finalizing work plans. Any sloughing or water that may collect in the drilled holes should be removed prior to pouring grout. Grout should be readily available on site at the time the holes are drilled and cased. If groundwater seepage is encountered, we recommend that the concrete be tremied from the bottom of the holes to displace the groundwater to the surface. Extra Portland Cement may also be placed in the bottom of the holes to reduce the effects of seepage. The spoils from the soldier pile excavations are expected to be moisture -sensitive materials and should be removed from the site. We should be retained to monitor on site activities during the shoring wall installation on a full-time basis. 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. We also recommend that a drainage system consisting of minimum 6-inch diameter perforated PVC pipe surrounded by a minimum of one foot of drain rock and the drain rock entirely wrapped in a heavy-duty filter fabric should be placed within the area behind the shoring wall to allow additional drainage through the planned shoring wall. The drain should be routed to the bottom of the slope. Also, all wall backfill should consist of 2-inch clean crushed rock compacted to structural fill specifications as discussed in this report. NELSON GEOTECHNICAL ASSOCIATES, INC.