6101 23RD DR W NORPRO Geotech Report 2025-07-29

June 3, 2011 Project No. T-6578 5.6 Retaining Walls Cast-in-Place The magnitude of earth pressure development on below-grade walls, such as basement or retaining walls, will partly depend on the quality of the wall backfill. We recommend placing and compacting wall backfill as structural fill as described in Section 5.2 of this report. To guard against hydrostatic pressure development, drainage must be installed behind the wall. A typical wall drainage detail is shown on Figure 4. With wall backfill placed and compacted as recommended and drainage properly installed, unrestrained walls can be designed for an active earth pressure equivalent to a fluid weighing 35 pcf. For restrained walls, an additional uniform lateral pressure of 100 psf should be included. For evaluating the walls under seismic loading,a uniform earth pressure equivalent to 8H psf, where H is the height of the retained earth in feet,can be used. These values assume a horizontal backfill condition and that no other surcharge loading, such as traffic,sloping embankments, or adjacent buildings, will act on the wall. If such conditions exist, then the imposed loading must be included in the wall design. Friction at the base of the wall foundation and passive earth pressure will provide resistance to these lateral loads. Values for these parameters are provided in Section 5.4 of this report. Rockeries • I As discussed, in our opinion, soil conditions would be suitable for using rockeries to face near-vertical cuts required along the eastern property line and structural fill in the northwest corner of the site. It should be noted that rockeries are not engineered structures that are designed to retain earth in a manner similar to a cast-in-place concrete or gravity block wall systems. Rocks used to construct the wall will by virtue of their mass enhance stability; however, the soil against which the rockery is constructed must be inherently stable and able to stand unsupported in a near-vertical condition. Based on our test pits, medium dense grading to very dense glacial till deposits will be exposed in the cut face 1 along the eastern property line. It is our opinion that an unreinforced rockery may face a near-vertical cut to the planned exposed height of 7.5 feet maximum. A fill rockery with a maximum height of four feet is planned in the , northwest margin of the site. Recommended eight-foot tall cut and four-foot tall fill rockery details are shown on Figure 5. If till rockeries over four feet in height are needed, the fill behind the rockery should be reinforced. We can provide a reinforced rockery design for a rockery of up to ten feet in height using a geotextile I reinforcement, if needed. 5.7 Drainage, I Surface I Final exterior grades should promote free and positive drainage away from the building areas. We recommend providing a gradient of at least three percent for a minimum distance of ten feet from the building perimeter, except in paved locations. In paved locations, a minimum gradient of two percent should be provided, unless provisions are included for collection and disposal of surface water adjacent to the structure. 111 Page No. 10