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353 Main Street Apartments <br />Redwood City, California <br />May L, 20L8 <br />(Original Report Dated November 78,2016) <br />traffic and may undergo deep rutting. Therefore, the pad grade may need to be stabilized to <br />allow for the smooth operation of the construction process. lf it is deemed necessary during the <br />construction phase of the project to stabilize the subgrade, the soil subgrade may be stabilized <br />by aeration and recompaction, or removal and replacement. Another alternative would be to <br />mix high calcium quick lime in the top L2 to LB inches of the floor subgrade. The nature and <br />percentage of additive needed to stabilize the subgrade will be determined at the time of grading. <br />Site Preparation and Grading <br />The site is currently occupied by a one story medical building. Additionally, undocumented fill <br />on the order of 6.5 to L0 feet was encountered over soft Bay Mud. Demolition of the existing <br />medical building is anticipated to disturb the ground. Due to ground disturbance and <br />undocumented fills, the anticipated grading operations would include over-excavation and <br />recompaction in the building foot print, perimeter fire lanes, and driveway areas constructed at <br />grade. <br />Additional grading work is anticipated to include backfill work related to placement of new utility <br />lines, and grading work related to new pavements. Grading operations are discussed in detail in <br />the Recommendations section of this report. <br />Soil Expansion Potential <br />An Atterberg limits test was performed on a sample of the fill material resulting in a plasticity <br />index (Pl) of 1-2. ln our boring logs, we indicate the fill material as being variable, consisting of <br />mixtures of lean and fat clays, gravels, and sands. Therefore, we anticipate the undocumented <br />fill in the upper 6.5 feet to have variable expansive potential (low to high). <br />ln general, expansive soils tend to swell with increases in soil moisture and shrink as the soil <br />moisture decreases. The volume changes that the soils undergo in this cyclical pattern can stress <br />and damage foundations, slabs, and other improvements if precautionary measures are not <br />incorporated into the design and construction procedures. <br />Liquefaction <br />During our subsurface exploration, potentially liquefiable materials were encountered at the site <br />and our analysis indicates liquefaction related settlement to be on the order of 0.4 to 2.L inches. <br />Differential settlement up to l-.7 inches over a distance of approximately 75 feet should be <br />anticipated. Our analysis showed lateral spreading on the order of 5 to 48 inches. Ground <br />improvement is recommended. <br />301842-001 t4 1610-038.SER.REV2 <br />7.B. - Page 72