5034 OCEAN AVE Geotech Report 2022-10-25

against the wall to prevent the build-up of hydrostatic pressure on the wall. The chimney drain should consist of a minimum 12 inch width of pea gravel or 3/4 inch washed drain rock place immediately adjacent to concrete wall extending from the footing drain to within 2 feet of the ground surface. The upper two feet should be backfilled with a low permeability soil to discourage surface runoff from entering the wall drainage system. Approved drainage boards, such as Inca Mat or Mira Drain, should be placed to extend from approximately two feet below the top of the wall down to hydranlically tie into the footing drain system. Backfill of the foundation walls outside of the chimney drain should be placed in approximate 12 inch loose lifts and compacted to a medium dense condition around 90 percent of the modified Proctor maximum dry density. A higher degree of compaction is not recommended as this may increase the pressures acting on the basement walls. The onsite soil may be used for wall compaction provided that the soil moisture content will allow adequate compaction of the wall backfill. Keeping the excavated soil from the foundation excavation covered with plastic sheeting will help insure that the soil may be used for wall backfill.. Floor Support The residence will utilize both crawl space and slab-on grade floors. The crawlspace soil should be covered with a moisture barrier to reduce the potential for moisture transfer from the ground. The slab-on-grade floor should be cast atop medium dense or denser native sand or compacted structural backfill around the foundation elements. A capillary break of 4 inches ofpea gravel should be placed atop the prepared floor subgrade. A moisture barrier should be placed atop the capillary break material prior to casting the floor slab. All concrete placements should be performed in accordance with current American Concrete Institute(ACI) standards. Drainage Considerations A perimeter foundation drain should be established to protect the foundationicrawlspace from ground water intrusion. The levelof the foundation drain should,be set at, or slightly below,the base of the footing elevation. The drain should consist of 4 inch diameter,rigid,perforated,PVC drain pipe and should be set to allow for gravity discharge. The drain pipe should be surrounded by a minimum of 6 inches ofpea gravel or washed drain rock. Roof drains should not tie into the footing drain but should be collected in a separate,tightline drain. The property was underlain by dense sand sediments with a.moderate capacity to infiltrate storm water runoff It is our understanding that an infiltration trench will be excavated across the north side of the property. It is our opinion that a properly developed infiltration trench will allow the majority of storm water runoff to infiltrate back into the ground. The overflow out of the french should be set to discharge at the northeast corner of the property. Conclusion Based on our site reconnaissance and subsurface explorations the site appears to be suitable for the proposed development provided the recommendations presented herein are properly implemented. The proposed replacement of the single family residence will not have an adverse affect on the subject property or on adjacent properties. Our findings and recommendations provided in this report were prepared in accordance with generally accepted principles of engineering geology and geotechnical engineering as practiced in BGC, plic 14267 209th Avenue NE Woodinville, WA 98077 (425) 273-5062