5901 23RD DR W Geotech Report 2025-07-29

I October 22, 2007 Project No.T-5922-I The native glacially-consolidated soils are very dense and are not susceptible to seismically induced liquefaction. Therefore, the site is not a seismic/liquefaction hazard area. Per Chapter 16 of the 2003 International Building Code (IBC),indicates site class"C" should be used for design of site structures. 5.0 DISCUSSION AND RECOMMENDATIONS 5.1 General Based on our study, in our opinion, there are no geotechnical conditions that would preclude development of the site, as planned. The buildings can be supported on conventional spread footing foundations bearing on competent native soils below the organic surface layer or on structural fill placed and compacted above these native soils. Floor slabs and pavements can be similarly supported. The site soils contain a sufficient amount of fines(silt-and clay-sized particles)such that they will be difficult to compact as structural fill when too wet or too dry. Accordingly, the ability to use the soils from site excavations as structural fill will depend on their moisture content and the prevailing weather conditions at the time of construction. If grading activities will take place during the winter season, the owner should be prepared to import free-draining granular material for use as structural fill and backfill. We expect that wintertime ,. construction may also necessitate significant efforts to maintain a firm, stable, and relatively dry working subgrade. The following sections provide detailed recommendations regarding these issues and other geotechnical design considerations. These recommendations should be incorporated into the final design drawings and construction specifications. 5.2 Site Grading Preparation n G g To prepare the site for construction, all vegetation, organic surface soils, and other deleterious materials should be stripped and removed from the site. On average, a stripping depth of about 12 inches should be expected to remove the organic surface layer. Stripped vegetation debris should be removed from the site. Organic soils are not suitable for use as structural fill, but may be used for limited depths in nonstructural areas or for landscaping purposes. Once clearing and grubbing operations are complete,cuts and fills can be made to establish desired finish grades. We recommend proofrolling all exposed surfaces to determine if any isolated soft and yielding areas are present. Proofrolling using heavy rubber-tired construction machinery should be performed both in fill and cut areas that wiIl provide direct support for new construction. If excessively yielding areas are observed and cannot be stabilized in place by compaction, the affected soils should be removed to firm bearing and grade restored with structural fill. If the depth of excavation to remove unstable soils is excessive, the use of geotextile fabrics, such as Mirafi 500X or an equivalent fabric, can be used in conjunction with clean (no soils fines) granular structural fill to limit the depth of removal. hi general, experience has shown that a minimum of 18 inches of clean granular structural fill over the geotextile fabric should establish a stable bearing surface. A representative of Terra Associates, Inc. should observe grading operations to verify soils conditions are as expected and cut and fill subgrade is stable and suitable for support of new construction. I Page No.7