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330 Land Company, LLC Arroyo Lago <br />9785.004.001 Design-Level Geotechnical Report <br /> <br /> <br /> Page | 17 April 16, 2024 <br />Latest Revision October 31, 2025 <br />5.3.1.2 Option 2: Thickened Mat or Deep Foundations <br /> <br />As an alternative to overexcavation of fill, buildings within fill slope areas may be founded on <br />either a thickened structural mat designed to tolerate the differential settlements, or a deep <br />foundation system consisting of cast-in-drilled-hole (CIDH) piers. We understand this is not the <br />preferred option. Thickened mat and deep foundation recommendations can be provided under <br />separate cover if requested. <br /> <br />5.3.2 Emergency Swale <br /> <br />We recommend that the differential fill thickness across any lot be no greater than 10 feet. Local <br />subexcavation of soil material and replacement with compacted fill may be needed to achieve this <br />recommendation. <br /> <br />5.4 ACCEPTABLE FILL <br /> <br />5.4.1 On-Site Existing Fill <br /> <br />On-site soil material may be suitable as fill material provided it is processed to remove <br />concentrations of organic material, debris, and particles greater than 8 inches in maximum <br />dimension. On-site soil material should be placed in a manner that prevents nesting of larger <br />particles, potentially generating voids. <br /> <br />5.4.2 Import Fill <br /> <br />Ideally, imported fill materials should be environmentally clean, free of debris, and have a plasticity <br />index less than 20 and have at least 20 percent passing the No. 200 sieve. Due to the residential <br />nature of the proposed project, environmental testing should also be performed on imported fill. <br />We should be allowed to sample and test the proposed imported fill materials at least 72 hours <br />prior to delivery to the site. <br /> <br />If desirable, ENGEO should be contacted to evaluate the appropriateness of import material that <br />does not meet the above criteria. <br /> <br />5.5 OVER-OPTIMUM SOIL MOISTURE CONDITIONS <br /> <br />The contractor should anticipate encountering excessively over-optimum (wet) soil moisture <br />conditions during winter or spring grading, or during or following periods of rain. Wet soil can make <br />proper compaction difficult. Wet soil conditions can be mitigated by: <br /> <br />1. Frequent spreading and mixing during warm dry weather; <br />2. Mixing with drier materials; <br />3. Mixing with a lime, lime-fly ash, or cement product; or <br />4. Stabilizing with aggregate, geotextile stabilization fabric, or both. <br /> <br />Options 3 and 4 should be evaluated and approved by a representative of our firm prior to <br />implementation. <br />