ARCHIVED REPORTS_2019 SOIL MGMT PLAN (JULY-REVISED)

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Murphy Parkway Warehouse December 19, 2016 Job No. 146-618 Page 4 and caving soils may require formwork to keep them open. The surface soils include low permeability layers and have variable drainage characteristics. The surface soils have high silt contents that render them sensitive to moisture contents. High moisture content soils are likely to be unstable under construction equipment, and require considerable aeration in order to achieve a moisture content that will allow compaction. The surface soils are likely to have high moisture conditions during the wet season and for several weeks following rains or irrigation. Subsurface soils within a few feet of groundwater are likely to have high moisture contents year round. The potential for high soil moisture contents should be considered in construction scheduling. SOIL LIQUEFACTION POTENTIAL Soil liquefaction is the loss of strength of low- to no- cohesion soils (usually sands) that occurs when pore water pressure exceeds the confining stress (weight) of the soils. Liquefaction normally occurs only under saturated conditions and in soils with a low relative density. Liquefaction can occur during earthquakes as vibrations induce soils to readjust to a more compact state. Experience has shown that earthquake induced liquefaction normally occurs only within the upper 50 to 60 feet of the soil profile. The test borings show loose to medium dense sands and sandy silts within the upper nine feet. Layers of medium dense to dense sandy soils are indicated between depths of six and 50 feet. The soils below depths of 13 to 14 feet below the building pad level are likely to be saturated year round. Slightly higher groundwater levels may be possible, but the duration of such high groundwater levels is expected to be limited. We have used the methods of Seed and others as implemented in the LiquefyPro software by CivilTech Corporation to assess the liquefaction susceptibility of the sandy soils, as well as to evaluate potential settlements of the loose near surface soils during seismic shaking. The method correlates standard penetration resistance and liquefaction potential based on historical case studies. In determining liquefaction potential, groundwater depth, confining pressures, and, intensity and duration of potential ground shaking are considered. Probabilistic seismic hazards mapping by the United States Geological Survey indicates that the peak ground acceleration produced by maximum credible earthquakes on nearby faults (10 percent probability of exceedance in 50 years) is likely to be on the order of 0.28 g. Interpretations according to the ASCE 7-10 standard indicates that the peak ground acceleration produced by maximum credible earthquakes with a two percent probability of exceedance in 50 years is likely to be on the order of 0.43g. The controlling earthquakes in developing these accelerations appear to mostly be events of magnitude 6.5 to 6.7 occurring within the Coast Range/Central Valley (CRCV) boundary zone about 21 kilometers to the southwest. Using these earthquake data, our analysis indicates that seismic induced liquefaction on this project is unlikely, although some sandy soils at depths of near 40 feet may approach a state of liquefaction under the highest levels of shaking. Settlements of the soils during maximum seismic shaking are estimated to be on the order of one quarter inch. The results of the analyses can be viewed on Plate 25, Liquefaction Analysis.