3800 RIVERFRONT BLVD Geotech Report 2023-05-04

March 26, 2019 HWA Project No. 2015-061-21 Task 600-7 4.4.9 Trench Backfill Placement and Compaction Proper placement and compaction of the trench backfill is extremely important to limit future settlement of the ground surface along the trench. Trench backfill should be uniformly moisture conditioned to within about 2 percent of optimum moisture content prior to placement in the trench. Properly prepared backfill, greater than 2 feet above the pipe bedding, should be placed in uniform loose lifts not to exceed 12 inches and densely compacted in a systematic manner using appropriately sized compaction equipment to achieve at least 95 percent of the maximum dry density as determined using ASTM D-1557. Smaller loose lifts may be necessary to achieve compaction where hand held compaction equipment such as jumping jacks, hoe-packs or plate compactors are used. The contractor should develop compaction methods that consistently produce adequate compaction levels. Observation and testing of trench backfill placement by a representative of the Geotechnical Engineer is recommended to help the contractor achieve proper backfill preparation and uniform moisture conditioning, loose lift thickness control and application of appropriate compaction effort. During placement of the initial lifts, the trench backfill material should not be bulldozed into the trench or dropped directly on the pipe. Furthermore, heavy vibratory equipment should not be permitted to operate directlyover the pipe until a minimum of 2 feet of backfill has been placed p pP over the pipe bedding to an in-place density of at least 90 percent of the maximum dry density as determined using ASTM D-1557. ' 4.5 PAVEMENT DESIGN Due to the anticipated differential settlements along the roadway alignment, we recommend that the roadway section be paved with relatively flexible hot mix asphalt (HMA) and not Portland Cement Concrete(PCC). Due to anticipated settlements, increased pavement maintenance will be required throughout the life of the roadway. We expect that this increased maintenance will include more frequent crack sealing and overlays as the roadway deforms due to settlement of the refuse and alluvial soils. 4.5.1 Pavement Subgrade Preparation As indicated in Section 4.7, we understand that utility installation along the Riverfront Boulevard is proposed for the spring of 2019. Given the moisture sensitive nature of the near surface fill along the road alignment, we expect that the utility installation procedure will disturb the subgrade soils along the road alignment. Therefore, we recommend the following subgrade preparation measures for the roadway. We recommend that roadway subgrade preparation take place during the dry summer months, after utility installation is completed. Once all utilities within the roadway are installed and Geotechnical Report Revision 3 26 2019.doc 18 HWA GEOSCIENCES INC.