3620 W MUKILTEO BLVD Geotech Report 2025-08-13

Geotechnical Engineering Evaluation Mukilteo Boulevard Development Everett,Washington March 31, 2003 NGA File No.366503 Page 12 condition. Active earth pressures and at-rest earth pressures can be calculated based on equivalent fluid density. Equivalent fluid densities for active and at-rest earth pressure of 35 pounds per cubic foot (pcf) and 60 pcf,respectively,may be used for design of a retaining wall with a level backfill. These values assume that granular soils are used for wall backfill and that the backfill adjacent to the wall is well-compacted • and drained. The preceding values do not include the effects of surcharges such as those due to foundation loads, vehicle loads, or other surface loads. Surcharge effects should be considered where appropriate. All wall backfill should be well-compacted. Care should be taken to prevent the buildup of excess lateral soil pressures due to overcompaction of the wall backfill. This can be accomplished by placing wall backfill in 8-inch lifts within a distance equal to one-half the height of the wall. Compaction close to the wall should be accomplished with small,hand-operated compactors. Permanent drainage systems should be installed for retaining walls as described in the Subsurface Drainage subsection. Slabs-on-Grade Slabs-on-grade should be supported on subgrade soils prepared as described in the Site Preparation and Grading subsection of this report. We recommend that all floor slabs be underlain by at least 6 inches of free-draining.sand or gravel for use as a capillary break. We recommend that the capillary break be hydraulically connected to the footing drain system to allow free drainage from under the slab. A suitable vapor barrier, such as heavy plastic sheeting(6-mil minimum), should be placed over the capillary break material. An additional 2-inch-thick sand blanket may be used to cover the vapor barrier. This sand blanket is to protect the vapor barrier membrane and to aid in curing the concrete. It will also prevent cement paste leaking down into the capillary break through the joints or tears in the vapor barrier. Pavement Subgrade Pavement subgrade preparation, and structural filling where required, should be completed as recommended in the Site Preparation and Grading and Structural Fill subsections of this report. The subgrade should be proofrolled with a heavy, rubber-tired piece of equipment to identify soft or yielding areas that require repair prior to placing the pavement section. Areas that are observed to pump or weave NELSON GEOTECHNICAL ASSOCIATES, INC. EXHIBIT. #, lc' pan r 13-n c 24/