The Mark at Eugene January 6, 2026 <br />Geotechnical Investigation and Seismic Hazard Study 16 Project No.: 2251077 <br />Eugene, Oregon Landmark Construction, LLC <br />24. Place and compact Base Aggregate within the finished foundation excavation <br />as specified in Item 6. <br />Retaining Walls <br />Retaining walls planned for the site should be designed and constructed as follows: <br />25. Design retaining wall footings using an allowable bearing pressure of <br />2,000 psf. This assumes all retaining walls will be constructed over at least <br />12 inches of compacted Base Aggregate placed over a firm subgrade. <br />26. Use an equivalent fluid density of 55 pcf to represent the lateral earth <br />pressure against drained walls. Undrained walls should be designed using an <br />equivalent fluid density of 90 pcf. These values assumes an at-rest condition <br />(i.e., the wall is relatively rigid against rotation) and level backfill. <br />27. Design the walls for sliding assuming a coefficient of sliding friction of 0.5 <br />between the base of the footings and the underlying Base Aggregate. <br />28. Excavate any unsuitable fill or soil under the footings for the new walls. The <br />depth and limits of any overexcavation should be confirmed by an FE <br />representative during construction. to provide the recommended section. <br />Complete the final excavation using a smooth-edged bucket to minimize <br />subgrade disturbance. <br />29. Place the base of the wall footings at least 1.5 feet below the finish ground <br />surface. <br />30. Place a minimum of 12 inches of compacted Base Aggregate under all wall <br />footings. As discussed above, additional fill may be required to replace <br />unsuitable fill. The Base Aggregate should extend at least 6 inches beyond <br />the limits of the footings. Compact the Base Aggregate as recommended in <br />Item 6. <br />31. Use Base Aggregate to backfill the wall. Place and compact the backfill as <br />recommended in Item 6. Use only light, walk-behind compaction equipment <br />within a distance of H/2, where H is the wall height, from the back of the <br />wall to avoid inducing excessive lateral pressures and possible wall <br />deflections. <br />32. Install a foundation drain in the backfill near the base of the walls. The drain <br />should consist of a 3 or 4-inch diameter, perforated or slotted PVC pipe. The <br />pipe should be bedded in Drain Rock and backfilled with Drain Rock at least <br />12 inches above the top of the pipe. Dispose of the collected water at an <br />appropriate location.