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Based on the settlement analysis (also tabulated on the spreadsheets in Appendix F) a total dynamic (liquefaction induced) settlement of 5.0=E inches could be expected at Boring No. B-1. The associated differential settlement is estimated to be on the order of 21/2 to 33: inches. The estimated differential settlement could be assumed to occur across a distance of 50 feet, indicating a maximum angular distortion of approximately 0.005 inches per inch. These settlements are considered to be in excess of the tolerances of a typical structure supported on shallow foundations. Therefore, this report provides recommendations for a mat foundation to support the proposed convenience store building. However, it should be noted that even with the use of a mat foundation, minor to moderate repairs, including repair of damaged drywall and stucco, etc., would likely be required after the occurrence of liquefaction-induced settlements. Based on our understanding of the proposed development, it is considered feasible to support the proposed structure on a mat foundation. Such a foundation system can be designed to resist the effects of the anticipated differential settlements, to the extent that the structure would not catastrophically fail.Designing the proposed structure to remain completely undamaged during a seismic event that could occur once every 475 years (the code-specified return period used in the liquefaction analysis) is not considered to be economically feasible. Based on this understanding, the use of a mat foundation system is considered to be the most economical means of supporting the proposed structure. In order to support the proposed structure on a mat foundation the structural engineer should verify that the structures would not catastrophically fail due to the predicted dynamic differential settlements. Any utility connections to the structures should be designed to withstand the estimated differential settlements. It should also be noted that minor to moderate repairs, including re-leveling, restoration of utility connections, repair of damaged drywall and stucco, etc., would likely be required after occurrence of the liquefaction-induced settlements. The use of a mat foundation system, as described in this report, is typical for buildings of this type, where they are underlain the extent of liquefiable soils encountered at this site. The post- liquefaction damage that could occur within the building proposed for this site will also be typical or less than similar buildings in the vicinity of this project. However, if the owner determines that this level of potential damage is not acceptable, other geotechnical and structural options are available, including the use of ground improvement. 6.2 Geotechnical Design Considerations General The subsurface conditions encountered at the site generally consist of a surficial layer of fill soils underlain by low to moderate strength native alluvium. The near surface fill soils possess variable strengths and variable composition. Based on these characteristics, and the age of the existing development, the existing fill soils are considered to represent undocumented fill, not suitable for support of the proposed structure. In addition, the upper zone of native alluvium, encountered at depths of 3 to 4 feet is currently in a loose condition and possesses unfavorable '----2 SOUTHERN G&M Convenience Store #72 - Santa Ana, CA 4-* CALIFORNIA Project No. 16G123-1R 1</ GEOTECHNICAL Page 13 SoCalâ‚¬;ec