8417 EVERGREEN WAY Geotech Report 2022-10-25

Geotechnical Engineering Report-Revised lierracon Proposed CFT Retail •Everett,Washington February 1, 2018 ■Terracon Project No. 81185002 causing subgrade disturbance. A Terracon representative can help with monitoring and developing recommendations to aid in limiting subgrade disturbance. After asphalt removal and excavation to proposed new subgrade elevations, proofrolling should be performed with heavy rubber-tire construction equipment such as a fully loaded tandem-axle dump truck. A Terracon representative should observe proofrolling to aid in locating unstable subgrade materials. Proofrolling should be performed after a suitable period of dry weather to avoid degrading an otherwise acceptable subgrade and to reduce the amount of remedial work required. Unstable materials located during proofrolling should be stabilized as recommended by the Terracon representative. Replacement and densification in place are typical remediation methods. 4.2.2 Structural Fill For the purposes of this report, structural fill is defined as any fill placed above or immediately below utilities, below foundations, pavements, or slabs-on-grade. Prior to placement of structural fill, the subgrade should be in a firm and non-yielding condition and free from organics, existing fill, or demolition debris. The suitability of soil used for structural fill depends primarily on its grain-size distribution and moisture content when it is placed.As the fines content(the soil fraction passing the U.S. No. 200 Sieve) increases, soil becomes more sensitive to small changes in moisture content. Soil containing more than about 5 percent fines (by weight) cannot be consistently compacted to a firm, unyielding condition when the moisture content is more than 2 percentage points above or below optimum. Optimum moisture content is the moisture content at which the maximum dry density for the material is achieved in the laboratory following ASTM procedures. The shallow silty sand fill and glacial till observed in our borings throughout the site generally appears to be suitable for reuse as structural fill from a compositional perspective. However,these soils are moisture sensitive and may become unusable if exposed to moisture. During periods of wet weather, we recommend that soil stockpiles intended for reuse be covered with plastic sheeting after excavation to maintain their native moisture content. We recommend that imported soil intended for use as structural fill consist of"common"or"select" granular material, depending on the weather conditions at the time of placement and the anticipated weather conditions until the fill is protected. These materials are defined below: ® Select Fill -"Select"granular fill is recommended for use in wet weather conditions. Select fill should meet the general requirements of WSDOT Section 9-03.14(1), Gravel Borrow or Section 9-03.14(2), Select Borrow. The percent passing the US No. 200 mesh sieve should, however, be modified from the WSDOT specification to a maximum of 5 percent by weight. Select fill can generally be placed and compacted in a wider variety of weather conditions than Common fill. Responsive ■ Resourceful m Reliable 6