600 RIVERSIDE RD Geotech Report 2022-10-25

P Landau Associates I or if wet weather construction is anticipated, Gravel Backfill for Pipe Zone Bedding meeting the requirements Section 9-03.12(3) of the 2016 WSDOT Standard Specifications should be used. Pipe bedding material and pipe zone backfill should be brought up evenly around the pipe in relatively horizontal lifts not exceeding 6 inches, and worked under the haunches of the pipe by slicing with a shovel, vibration, or other approved procedures. Pipe zone backfill should extend 6 inches above the crown of the pipe. Pipe bedding and pipe zone backfill should be compacted to at least 90 percent of its maximum dry density as determined in accordance with the ASTM D1557 test procedure (modified Proctor). 3.6.5 Trench Backfill and Compaction Criteria The onsite soil within the depths of the proposed utility trenches is expected to consist primarily of dredged sand fill and alluvial sands (upper sand unit). This soil is expected to be suitable for use as trench backfill; however, some of the soil could be above optimum, indicating that moisture conditioning could be required. In addition, the moisture content would be expected to increase to percentages possibly well above optimum if the soil is obtained from beneath the groundwater table or construction in conducted during wetter months. Any silt, clay, or organic -rich soil that is encountered within the proposed utility trench excavations will not be suitable for use as trench backfill beneath paved roads or where several inches of post -construction settlement is not tolerable. This fine-grained soil could be used as backfill above the proposed pipes in unimproved or landscaped areas where several inches (or more) of post -construction is acceptable. If earthwork must be performed during periods of wet weather, and appropriate levels of compaction cannot be achieved with onsite soil, or if sufficient fill material is not available onsite, we recommend fill material be imported to backfill trenches. Imported trench backfill should meet the requirements for Bank Run Gravel for Trench Backfill in Section 9-03.19 of the 2016 WSDOT Standard Specifications. The fines content of the trench backfill may be increased somewhat during dry weather conditions, provided the soil is not too wet for proper compaction. If wet weather construction is anticipated, the amount of fines should be limited to 5 percent or less, based on a wet sieve analysis of that portion passing the %-inch sieve. It is recommended that the trench backfill be placed in 8- to 10-inch, loose lifts and compacted using mechanical equipment to at least 90 percent of the maximum dry density as determined by test method ASTM D 1557 (modified Proctor). The upper 3 ft of backfill should be compacted to at least 95 percent of the maximum dry density. In areas where several inches of post -construction backfill settlement can be tolerated, such as unimproved or landscaped areas, backfill compaction could be reduced to 85 percent. I Geotechnical Engineering Report 0121030.010.011 Riverside Business Park March 22, 2018 Public Access Trails and Roadway Improvements 3-9