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 20 spills to buttress the slope in selected locations, placing erosion control matting on all exposed surfaces on the slopes, installing shallow drains to control surface and subsurface water flow, and re -plating the slope with deep-rooted vegetation. The final extent of such improvements should be detennined in the field at the time of construction. However, for planning purposes, areas of sloughing and slide debris would be over -excavated down to competent material and 4-foot wide benches created in these areas. All exposed areas on the slope should be covered with erosion control matting and appropriate vegetation. Shallow cut-off drains may need to be installed at strategic locations below the wall to divert water seepage away from sensitive areas. The drains typically consist of 4-inch perforated PVC pipes placed in 2- to Moot deep trenches filled with pea gravel or washed rock. All excavation spoils should be removed off the slope or placed and compacted in low areas as approved by NGA and the City. The drains would be routed to the bottom of the slope or to an appropriate discharge location. The areas below the wall that we have deemed at risk of further movement should be improved by re- grading the over-steepened/loosened areas using light -weight equipment and/or manual labor, removing the vegetative cover, compacting the exposed surface to a non -yielding condition, placing suitable erosion control systems on the prepared areas, and re -vegetating with deep-rooted drought -resistant plants. Final site grades should allow for drainage away from the top of the steep slope and the wall. If possible, the finished ground should be sloped at a gradient of three -percent minimum for a distance of at least 10 icet away front slope. In any case, all runoff'generated above the slope, including paved areas, roofs, footing drains, and yard areas should be collected and routed into it penuanent discharge location at the bottom of the slope. The discharge locations ol'the fightline pipe should consist of an 8-foot by 8-foot by I -foot thick rock spill pad to dissipate energy from flowing water. The tightline should be anchored to the slope and should be inspected periodically to ensure proper performance. USE OF THIS REPORT NGA has prepared this report for Rick and Ilolly Anderson and their agents for use in the planning and design of the development planned on this site only. The scope of our work does not include services related to construction safety precautions and our recommendations are not intended to direct the contractors' methods, techniques, sequences, or procedures, except as specifically described in our report for consideration in design. There are possible variations in subsurface conditions between the NELSON GEOTECHNICAL A. oOCIATES, INC. FMI