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EARTH STRATA GEOTECHNICAL SERVICES 18 March 30, 2023 Project Number 234812-10A Specific guidelines for concrete mix design are provided in 2022 CBC Section 1904.1 and ACI 318-19, Section 4.3 Tables 19.3.1.1 and 19.3.2.1 when the soluble sulfate content of earth materials exceeds 0.1 percent by weight. Based on limited preliminary laboratory testing, the onsite earth materials are classified in accordance with Tables 19.3.1.1 and 19.3.2.1 as having a negligible sulfate exposure condition. Therefore, structural concrete in contact with onsite earth materials should utilize Type I with a minimum 28 day compressive strength of 4,000 psi. Based on our laboratory testing of resistivity, the onsite earth materials in contact with buried steel should be considered moderately corrosive. Additionally, pH values below 5.6 and above 9.1 are recognized as being corrosive to many common metallic components. The pH values for the earth materials tested were lower than 9.1 and higher than 5.6. If building slabs are to be post tensioned, the post tensioning cables should be encased in concrete and/or encapsulated in accordance with the Post Tensioning Institute Guide Specifications. Post tensioning cable end plate anchors and nuts also need to be protected if exposed. If the anchor plates and nuts are in a recess in the edge of the concrete slab, the recess should be filled in with a non-shrink, non-porous, moisture-insensitive epoxy grout so that the anchorage assembly and the end of the cable are completely encased and isolated from the soil. A standard non-shrink, non-metallic cementitious grout may be used only when the post tension anchoring assembly is polyethylene encapsulated equivalent to that offered from a PTI plant or similar. The preliminary test results for corrosivity are based on limited samples, and the initiation of grading may blend various earth materials together. This blending or imported material could alter and increase the detrimental properties of the onsite earth materials. Accordingly, additional testing for chlorides and sulfates along with testing for pH and resistivity should be performed upon completion of grading. Laboratory test results are presented in Appendix C. RETAINING WALLS Active and At-Rest Earth Pressures Foundations may be designed in accordance with the recommendations provided in the Tentative Foundation Design Recommendation section of this report. The following table provides the minimum recommended equivalent fluid pressures for design of retaining walls a maximum of 6 feet high. The active earth pressure should be used for design of unrestrained retaining walls, which are free to tilt slightly. The at-rest earth pressure should be used for design of retaining walls that are restrained at the top, such as basement walls, curved walls with no joints, or walls restrained at corners. For curved walls, active pressure may be used if tilting is acceptable and construction joints are provided at each angle point and at a minimum of 15 foot intervals along the curved segments. MINIMUM STATIC EQUIVALENT FLUID PRESSURES (pcf) PRESSURE TYPE Active Earth Pressure 40 63 At-Rest Earth Pressure 60 95 2130 E 4th St 2/11/2025