6202 ASSOCIATED BLVD Geotech Report 2022-10-25

Proposed Everett Warehouse ZipperGeo Project No. 2152.01 March 5, 2019 is avoided. Any surface runoff directed towards softscaped slopes should be collected at the top of the slope and routed to the bottom of the slope and discharged in a manner that prevents erosion. Permanent Foundation Wall Drainage Adequate drainage measures must be installed to collect and direct subsurface water away from subgrade walls. All backfilled walls should include a drainage aggregate zone extending a minimum of two feet from the back of wall for the full height of the wall and wide enough at the base of the wall to allow seepage to flow to the footing drain. The drainage aggregate should consist of material meeting the requirements of WSDOT 9-03.12(2), Gravel Backfill for Walls. A minimum 4-inch diameter, perforated PVC drain pipe should be provided at the base of backfilled walls to collect and direct subsurface water to an appropriate discharge point. We recommend placing a non -woven geotextile, such as Mirafi 140N, or equivalent, around the free draining backfill material. Pavements Pavement Life and Maintenance: It should be realized that asphaltic pavements are not maintenance - free. The following pavement sections represent our minimum recommendations for an average level of performance during a 20-year design life; therefore, an average level of maintenance will likely be required. A 20-year pavement life typically assumes that an overlay will be placed after about 10 to 12 years. Thicker asphalt, base, and subbase courses would offer better long-term performance, but would cost more initially. Conversely, thinner courses would be more susceptible to "alligator" cracking and other failure modes. As such, pavement design can be considered a compromise between a high initial cost and low maintenance costs versus a low initial cost and higher maintenance costs. Our recommendations for pavements provided in this section are based on recommendations presented in Chapter 4, Low -Volume Road Design of the 1993 AASHTO Guide for Design of Pavement Sections Low Volume Road Design. As part of our work, we completed a CBR test to evaluate pavement subgrade support characteristics. Our testing indicated a CBR value of about 34 for site soils compacted to 95% of the ASTM D1557 modified proctor maximum dry density. Pavement Pavement Design Criteria: No traffic loading was provided for this project. For pavement design, we assumed an 18-kip traffic level of 50,000 to 300,000 equivalent single axle loads, or low traffic levels as defined by AASHTO. For other design criteria, we assumed the following: • Inherent Reliability: 75 percent • Relative Quality of Roadbed Soil: Very Good Recommended Minimum Pavement Sections: Based on the above assumed design criteria, we recommend the following pavement sections. For light -duty pavements (parking space areas and low volume areas), we recommend 2 inches of asphalt concrete over 4 inches of crushed rock base course. Page 15