406 PECKS DR Geotech Report 2025-07-14

December 30th, 2021 G-5593 4730—Seahurst Ave,Washington 98203 Page 8 Utility trench backfill within the City right-of-way should be compacted to the specifications required by the City, sewer or water district. Observation and compaction testing may be required at the time of fill placement to document and verify that the compaction specifications are achieved. Pavements Provided the soil subgrade is dense and unyielding,we recommend an asphalt pavement section for light traffic loads consisting of 2 inches Class B asphalt concrete (1/2-inch HMA) over 4 inches of 5/8-minus crushed rock base. The pavement section for heavier traffic loads, such as for garbage trucks, should consist of 3 inches Class B asphalt concrete over 6 inches of 5/8-inch minus crushed rock base. The pavement section design should be provided by the project civil engineer. Pavement performance is strictly related to the condition of the underlying subgrade. If the subgrade is inadequate, settlement and movement of the subgrade, such as alligatoring, can be reflected up through to the pavement surface no matter what pavement section is constructed. If loose subgrade soils are present, we recommend improving the subgrade by placing the pavement section on a minimum of 2 feet of granular structural fill or crushed rock. The subgrade below the structural fill should be compacted prior to placement of the structural fill and be evaluated by the geotechnical engineer. An unstable condition my require the use of a woven geotextile to separate the underlying soil from the granular overlying structural fill. For on-site pavement, structural fill should be compacted to a minimum of 90 percent, except for the top 12 inches which should be compacted to 95 percent of the materials maximum dry density based on ASTM D-1557 (Modified Proctor). Prior to paving, the subgrade should be proof-rolled with a heavy piece of equipment, such as a loaded dump truck,under the observation of the geotechnical engineer, to verify that the subgrade is dense,unyielding, and suitable to support the pavement section. Soft or unstable subgrade identified during the proof-roll should be evaluated by the geotechnical engineer and stabilized prior to paving. LIMITATIONS The services described in this letter were prepared under the responsible charge of William Chang. William Chang is a geotechnical engineer as defined by EMC 19.4. William Chang GEO Group Northwest,Inc.