3535 RIVERFRONT BLVD Geotech Report 2023-02-22

September 24, 2018 HWA Project No. 2015-061-21 4.7.2 Sheet Pile Wall Design Sheet piles installed to resist lateral soil loading must be designed to resist the lateral earth pressures, as described in this section. These earth pressures have been developed from our boring B-101, and employ the strength parameters utilized in our stability analyses of the river bank slopes. In generalized terms, the existing stratigraphy at B-101, near the wall location, consists of: • Old Fill: Extending from the ground surface at El. +13.0 ft to El. -2.0 ft; • Peat/Alluvium: El. -2 to -7 ft; • Sandy Silt: El. -7.0 ft and El. -12.0 ft; and • Sand Alluvium: El. -12 ft to the depth of borehole penetration at 86 ft below ground surface. For design purposes, the level of the ground water table is of importance and may be assumed to be at the top of the wall for the worst case scenario, or some depth below the top of wall, if the designer has confidence in that level not being exceeded. We recommend the design ground water level on the bank side of the wall be assumed no lower than El. +9.0 ft. On the river side, we recommend the water level be assumed to be no lower than El. -2.0 ft, which we understand has a 100% exceedance probability. Because the sheet pile wall will significantly retard the flow of water toward the river, we recommend a net water pressure imbalance between the highest and lowest levels be assumed between the bank and river sides for lateral pressure/load determinations. For sheet pile wall design purposes, we recommend the active earth pressure parameters provided in Table 4 be employed. Active earth pressures should be applied at the back of the sheet pile wall structure in a down slope direction. The passive earth pressure parameters are provided in Table 5. Passive earth pressures should be applied to the outside of the sheet pile wall or at the front of the structure, acting in an upslope direction. These earth pressures are based on equivalent fluid unit weight concepts. For passive pressures, we have assumed that due to scour or slope failure the sheet piles could be exposed to the top of the Sandy Silt layer (El. -7 feet). River bottom soils, comprised of Sandy Silt and Sand Alluvium may be assumed to remain in place to provide passive earth pressure restraint for the wall below this level, and may be considered to have the same properties on both sides of the wall. Note that for the below ground water table (GWT) condition, the hydrostatic pressure has been included in the equivalent fluid pressure values provided. 111 For passive earth pressure restraint considerations, hydrostatic pressures may be assumed to balance each other below El. -2.0 ft, or whatever elevation is assumed for lowest river stage. No hydrodynamic effects have been incorporated into the design parameters as it is assumed that the water will not act independently of the soil structure, and that any added hydrodynamic pressures attributable to the river water in contact with the sheet pile wall would only add to buttressing effects of the wall. No factors of safety have been incorporated in any of the earth pressure Final Geotechnical Report-3-Acre Park.docx 21 HWA GeoSciences Inc.