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

October 25, 2015 YMCA - Everett L&A Job No. 15-089 Page 11 clean, sandy soils. Heavy compaction equipment should not be allowed within the walls of a horizontal distance equal to that of the wall heights. A 4-inch perforated PVC footing drain pipe, as recommended in the DRAINAGE CONTROL section of this report, should be provided for retaining walls. The drain lines should be hydraulically connected to the drainage blanket behind the walls and tightlined to a storm sewer. STRUCTURAL FILL Structural fill is the fill that supports structural or traffic load. Structural fill should consist of clean granular soils free of organic and other deleterious substances and with particles not larger than three inches in size. Structural fill should have a moisture content within one percent of its optimum moisture content at the time of placement. The optimum moisture content is the water content in the soils that enable the soils to be compacted to the highest dry density for a given compaction effort. Onsite soils meeting the above requirements may be used as structural fill. Imported material to be used as structural fill should be clean, free-draining, granular soils containing no more than 5 percent by weight finer than the No. 200 sieve based on the fraction of the material passing No. 4 sieve, and should have individual particles not larger than four inches. The ground over which structural fill is to be placed should be prepared in accordance with recommendations in the SITE PREPARATION AND GENERAL GRADING and EXCAVATION AND FILL SLOPES sections of this report. Structural fill placed on ground steeper than 20% should be structurally supported. Ground steeper than 15% should be stepped with vertical step no more than 3 feet before placing structural fill. Structural fill LIU & ASSOCIATES, INC.