3800 RIVERFRONT BLVD Geotech Report 2023-05-04

March 26, 2019 HWA Project No. 2015-061-21 Task 600-7 I We expect that supporting the sewer system with the proposed pile supported buildings will involve hanging the sewer line from the bottom of the proposed building floor slab or grade beams. To prevent differential settlements between pipes and utility structures, all required Imanholes and cleanouts should also be supported by the proposed pile supported buildings. We recommend that all sewer related elements be backfilled with pea gravel. This will allow the pea gravel to flow off or around the structural supported elements as the surrounding soils settle. A Iseparator fabric should be placed over the pea gravel wherever concrete is to be poured over the pea gravel or soil is to be placed over the pea gravel. The sewer system should continue to be pile supported between pile-supported buildings. Failure to maintain this pile support will result in significant differential settlement and potential system failures. We expect that the proposed sanitary sewer system, associated with the Phase 1 development, Iwill be grade supported from Lift Station 43 to the southern end of the proposed pile-supported buildings. Long term settlement is expected to occur across this distance. We recommend that I this segment of grade supported system be designed with an increased fall that will allow for proper function after as much as 30 inches of settlement occurs. Flexible connections should be constructed at the point that the proposed sewer transitions from grade-supported to pile- supported. 4.4.4 Storm Drain IWe expect that the storm drain system for Riverfront Boulevard will be constructed conventionally within the roadway. Therefore, the storm drain system is expected to undergo the I same deferential settlements as the roadway. As shown in Figure 5, our analysis indicates that several low areas along the roadway are expected to develop over time. To reduce future ponding along the roadway, we recommend that additional storm drain inlets be positioned at Ilocations where long-term settlements are expected to be greatest. Additionally, we recommend that the storm drain system be designed with sufficient fall to ensure that the system will function after as much as 30-inches of settlement occurs. 4.4.5 Utility Excavation Considerations I The near surface soils along the roadway alignment consist of varying amounts of fill soils over refuse. The fill soils consist of silty sands that were compacted to 90 percent of modified proctor at the time of placement. In some areas the fill soils possess increased sand content. Available Igeotechnical explorations indicate that the thickness of the fill soils vary along the road alignment from as much as 20 feet to as little as 2 feet in some areas. Fill thickness appears to be I greatest south of Station 30+00 and thin out north of Station 30+00. An 18-inch thick layer of cement treated soils should be expected within the near surface soils along portions of the roadway alignment. Landfill refuse exists below the fill at all locations along the roadway I alignment. Excavations through each of these material types may result in specific construction challenges. These challenges are addressed below. I Geotechnical Report Revision 3 26 2019.doc 15 HWA GEOSCIENCES INC.