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Phelan Development Holly Master Plan - Buildings H & 1 15188.000.006 Geotechnical Exploration 3.2 EXPANSIVE SOIL We observed potentially expansive lean to fat clay near the surface of the site in our test pit excavations and in Boring 4-1301. Our laboratory testing indicates that this soil exhibits moderate shrink/swell potential with variations in moisture content. Expansive soil can change in volume with changes in moisture. It can shrink or swell and cause heaving and cracking of slabs-on-grade, pavements, and structures founded on shallow foundations. Building damage due to volume changes associated with expansive soil can be reduced by deepening the foundations to below the zone of significant moisture fluctuation. To reduce the potential for damage to the planned building, we recommend that the upper 18 inches of the building pad extending at least 5 feet laterally beyond building areas be underlain by non-expansive fill (PI less than 12). Due to the lack of near-surface non-expansive soil and cost to import non-expansive soil, we recommend lime treatment of the upper 18 inches of the building pad extending at least 5 feet laterally beyond building areas to reduce the expansion potential of the on-site soil. We recommend that other structural elements, such as pavements and flatwork be designed for moderately expansive soil conditions. We also provide specific grading recommendations for compaction of clay soil at the site later in this report. The purpose of these recommendations is to reduce the swell potential of the clay by compacting the soil at a high moisture content and controlling the amount of compaction. Expansive soil mitigation recommendations are presented in Section 4.1 of this report. 3.3 SEISMIC HAZARDS Potential seismic hazards resulting from a nearby moderate to major earthquake can generally be classified as primary and secondary. The primary effect is ground rupture, also called surface faulting. The common secondary seismic hazards include ground shaking and ground lurching. The following sections present a discussion of these hazards as they apply to the site. Based on topographic and Iithologic data, the risk of regional subsidence or uplift, soil liquefaction, lateral spreading, landslides, tsunamis, flooding or seiches is considered low to negligible at the site. 3.3.1 Ground Rupture Since there are no known active faults crossing the property, and the site is not located within an Alquist-Priolo Earthquake Fault Zone, it is our opinion that primary fault ground rupture is unlikely at the property. 3.3.2 Ground Shaking An earthquake of moderate to high magnitude generated within the region could cause considerable ground shaking at the site, similar to that which has occurred in the past. To mitigate the shaking effects, structures should be designed using sound engineering judgment and the 2019 California Building Code (CBC) requirements, as a minimum. Seismic design provisions of current building codes generally prescribe minimum lateral forces, applied statically to the structure, combined with the gravity forces of dead-and-live loads. The code-prescribed lateral forces are generally considered to be substantially smaller than the comparable forces that would be associated with a major earthquake. Therefore, structures should be able to: (1) resist minor earthquakes without damage, (2) resist moderate earthquakes without structural damage but with some nonstructural damage, and (3) resist major earthquakes without collapse but with some structural as well as nonstructural damage. Conformance to the current building code ENGEO December 13, 2021 Expect Exceltence