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be on the order of 0.35 to 0.15 for an upper and a lower level event, respectively. These
earthquakes would have respective Richter magnitudes of approximately 7.5 and 5.5. The lower
level event is one with a 50 percent probability of exceedance during a 50-year design life. This
is an event to 1965
similar the Seattle earthquake, and one that structures should be designed to
survive with little damage. The upper level earthquake represents a less likely (10 percent
probability of exceedarce) event for which structures might be expected to show structural -
damage, but would not collapse.
The sandy gradation of the onsite soils, together with the relatively shallow groundwater table,
make portions of these tri ese units susceptible to liquefaction during a seismic event. The
liquefaction potential of the soils underlying the proposed Fry's Superstore site was evaluated by
an empirical method using a direct correlation between observed ground motion and sampler
blow count data. We considered four typical soil profiles, corresponding to the soils encountered
m in borings at each of the proposed building comers with the groundwater table 4 to 7 feet below
r
ground surface. For the lower and upper level earthquakes, our results are as follows :
-- Lower Level Earthquake: A comparison of the induced cyclic shear stresses during a lower level
earthquake with the available cyclic shear strength indicates liquefaction would likely not occur
y within 40 feet of the ground surface.
�+ Upper Level Earthquake: A similar comparison for the upper level earthquake indicates
liquefaction would likely not occur within 40 feet of the ground surface.
3.6 SITE DRAI.tiAGE
Because the majority of the surficial site soiis are moisture sensitive and relatively impermeable,
both short- and long-term drainage control measures should be included in project design and
construction.
Over the short term, w believe site and construction drainage can be reasonably well controlled
by careful excavation practices. Typically, these include, but are not limited to, shallow upgrade
perimeter ditches or low earthen berms, and temporary sumps in excavations to collect seepage
i and prevent water from damaging exposed subgrades.
60213W 1 6011 R057 12 of 76
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