801 E CASINO RD Geotech Report 2022-10-25

Cascade High School Subsurface Exploration and Synthetic Turf Field Geotechnical Engineering Report Everett, Washington Design Recommendations subgrade. Engineering stabilization fabric should be used if needed to prevent contamination of the new structural fill by silt migration from below. After recompaction of the exposed ground is tested and approved, or a free -draining rock course is laid, structural fill may be placed to attain desired grades. Structural fill is defined as non -organic soil, acceptable to the geotechnical engineer, placed in maximum 8-inch loose lifts, with each lift being compacted to 90 percent of the modified Proctor maximum density using ASTM D-1557 as the standard. In the case of utility trench filling, the backfill may also need to be placed and compacted in accordance with current local codes and standards. The top of the compacted fill should extend horizontally outward a minimum distance of 3 feet beyond the locations of athletic field and pavement edges before sloping down at a maximum angle of 2H:1V. The contractor should note that any proposed fill soils must be evaluated by AESI prior to their use in fills. This would require that we have a sample of the material 72 hours in advance of filling activities to perform a Proctor test and determine its field compaction standard. Soils in which the amount of fine-grained material (smaller than the No. 200 sieve) is greater than approximately 5 percent (measured on the minus No. 4 sieve size) should be considered moisture -sensitive. Use of moisture -sensitive soil in structural fills should be limited to favorable dry weather conditions. The on -site soils contain significant amounts of silt and are considered to be highly moisture -sensitive. We anticipate that most or all of the existing soils will be above the optimum moisture content for compaction purposes. The reuse of on -site soils in structural fill applications is contingent on moisture -conditioning to a moisture content that allows compaction to a firm and unyielding condition at the specified level, if they are free of any excessively organic material, and is only permitted if specifically allowed by project plans and specifications. Construction equipment traversing the site when the soils are wet can cause considerable disturbance. If fill is placed during wet weather or if proper compaction cannot be obtained, a select import material consisting of a clean, free -draining gravel and/or sand should be used. Free -draining fill consists of non -organic soil with the amount of fine-grained material limited to 5 percent by weight when measured on the minus No. 4 sieve fraction with at least 25 percent retained on the No. 4 sieve. 8.2 Subsurface Drains (Underdrains) We recommend that a subsurface drainage system be provided below the new field due to the low permeability of the underlying existing fill and native sediments. The new underdrain system should consist of perforated pipes placed approximately 15 to 20 feet apart. The pipes should have an invert of at least 12 inches below final grade and be enveloped in washed pea gravel which freely communicates with the field surfacing. We defer to the field designer for March 20, 2017 ASSOCIATED EARTH SCIENCES, INC. DDV/pc-17WSIE001-2-Pro%ectrJ201700S1JKEJWP Page 8