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330 Land Company, LLC Arroyo Lago <br />9785.004.001 Design-Level Geotechnical Report <br /> <br /> <br /> Page | 9 April 16, 2024 <br />Latest Revision October 31, 2025 <br />3.1 EXISTING FILL <br /> <br />Based on review of current and previous subsurface explorations, as well as review of historical <br />aerial photographs, the site is predominately underlain by existing fill reportedly used to backfill <br />the historical quarry excavations. With exception of the fill placed within Busch Pit and the surficial <br />fill placed under the observation of Haley & Aldrich in 2018 and 2019, the underlying fill should be <br />considered undocumented due to the lack of placement records. The undocumented fill materials <br />may be highly variable, potentially compressible, and potentially susceptible to seismically induced <br />settlements. Given prior site history, decomposable debris may also be present within <br />undocumented fill materials that can contribute to settlement. We summarize the assumed depth of <br />undocumented fill of select explorations in the table below. <br /> <br />TABLE 3.1-1: Depth of Fill Observations During Current and Prior Exploration <br />EXPLORATION ID INTERPRETED BOTTOM OF FILL <br />DEPTH (feet, bgs) ELEVATION (feet NAVD88) <br />1-B1 - - <br />1-B2 - - <br />1-B3 88 271½ <br />1-B4 - - <br />1-CPT1 38½ 320½ <br />1-CPT2 162½ 198 <br />1-CPT3 - - <br />1-SCPT4 - - <br />1-CPT5 80½ 280 <br /> <br />Undocumented fill can undergo excessive settlement, especially under new fill or building loads. <br />Since the existing fill is heterogeneous in its makeup, the predicted differential settlements due to <br />existing fill may be similar, or only slightly less than predicted total settlements. <br /> <br />We discuss undocumented fill mitigation in Section 5.2 of this report. <br /> <br />3.2 EXPANSIVE SOIL <br /> <br />The existing undocumented fill encountered consists primarily of lean clay and fat clay with varying <br />amounts of granular soil. Based on our field exploration and laboratory testing on the fill material, the <br />existing clayey fill should be considered to have a moderate to high expansive potential. <br /> <br />Expansive soil changes in volume with changes in moisture. It can shrink or swell and cause <br />heaving and cracking of slabs-on-grade, pavements, and structures founded on shallow <br />foundations. Building damage due to volume changes associated with expansive soil can be <br />reduced by: (1) using a rigid mat foundation that is designed to resist the settlement and heave <br />of expansive soil, (2) deepening the foundations to below the zone of moisture fluctuation, i.e., by <br />using deep footings or drilled piers, and/or (3) using footings at normal shallow depths but <br />bottomed on a layer of select fill having a low expansion potential. <br /> <br />Successful performance of structures on expansive soil requires special attention during <br />construction. It is imperative that exposed soil be kept moist prior to placement of concrete for <br />foundation construction. It can be difficult to remoisturize clayey soil without excavation, moisture <br />conditioning, and recompaction.