3535 RIVERFRONT BLVD Geotech Report 2023-02-22

September 24, 2018 HWA Project No. 2015-061-21 I I considered reasonable for relatively loosely placed materials. No factors of safety have been applied to the values in Table 5. 4.8 PAVEMENT RECOMMENDATIONS I 4.8.1 Trail Pavement The 3-Acre Park trails and paths will be paved, with the majority being hot-mix asphalt (HMA) pavement. We recommend that paving be delayed as long as possible to limit the amount of I differential settlement experienced by the pavement. Greater differential settlement is expected where fill thicknesses vary below the pavement section. Differential settlements are likely to result in areas of premature pavement distress. 4.8.2 Design Traffic We anticipate the subgrade will consist primarily of imported compacted embankment materials. The City of Everett has indicated that the heaviest maintenance truck to use the trail will have a gross vehicle weight of 10,000 pounds and will be making 2 trips a week. For design we have I assumed that the compacted subgrade is generally composed of fine silt(river alluvium) with a resilient modulus of about 5,000 psi. For flexible pavements (HMA), the total ESAL value for a 20-year design life is about 200. For rigid(PCC)pavement the total number of ESALs is about 500 over a 40 year design life of the pavement. 4.8.3 New Hot-Mix Asphalt(HMA) Pavement Design IGiven the very low number of ESALs for this pavement design, non-structural distress from environmental factors will likely cause degradation of the pavement before the design loading causes structural distress. Accordingly, based on the non-structural distress considerations, we recommend the trailpavement section consist of at least 2 inches of HMA (Sections 5-04 & 9-02.1 WSDOT Standard Specifications) over 7 inches of CSBC/CSTC (Section 9-03.9(3) IWSDOT Standard Specifications) or 3 inches of HMA over 4 inches of CSBC/CSTC. The selection of the optimum asphalt binder type for the climate is critical to ensure long-term pavement performance. Use of the wrong binder can result in low temperature cracking or permanent deformation at high temperatures. Based on the climate in the project vicinity and WSDOT recommendations, Superpave Performance Grade binder PG 64-22 should be used. IPlacement of HMA should be in accordance with Section 5-04 of the 2018 WSDOT Standard Specifications. Particular attention should be paid to the following: • Themaximum hi thickness for HMAClass1/2-inch is0 3 feet (or 3 6 inches). The lift t c ess o /2 c c es). maximum lift thickness is stipulated by WSDOT (WSDOT, 2018). • HMA should not be placed until the engineer has accepted the previously constructed pavement layers. I Final Geotechnical Report-3-Acre Park.docx 24 HWA GeoSciences Inc.