4730 COLBY AVE SEPA 016 - 027 - YMCA Geotech Report 2025-04-14

October 25, 2015 YMCA - Everett L&A Job No. 15-089 Page 14 distance at least 1.5 times the depth of the foundations below the final grade. A coefficient of friction of 0.55 between the foundations and the subgrade soil may be used. The above recommended soil parameters are unfactored values, and a proper factor of safety should be used in calculating the resisting forces against lateral loads on the proposed residence. SLAB-ON-GRADE FLOORS Slab-on-grade floors, if used for the multi-use building, should also be constructed on firm unyielding subgrade soil prepared as outlined in the BUILDING FOUNDATION section of this report. Where moisture control is critical, the slab-on-grade floors should be placed on a capillary break which is in turn constructed on compacted subgrade soil. The capillary break should consist of a minimum 6-inch-thick layer of clean, free-draining, 5/8-inch crushed rock, containing no more than 5 percent by weight passing the No. 4 sieve. A vapor barrier, such as a 6-mil plastic membrane, may be placed over the capillary break, as required, to keep moisture from migrating upwards. DRIVEWAY/PARKING LOT PAVEMENT Performance of driveway/parking lot pavement is critically related to the conditions of the underlying subgrade soils. We recommend that the subgrade soil under driveway/parking lot be treated and prepared as described in the SITE PREPARATION AND GENERAL EARTHWORK section of this report. Prior to placing base material, the subgrade soil should be compacted to a non-yielding state with a vibratory roller compactor and proof- rolled with a piece of heavy construction equipment, such as a fully-loaded dump truck. Any areas with excessive flexing or pumping should be over-excavated and re-compacted or LIU & ASSOCIATES, INC.