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Liquefaction and Seismic Site Class

Liquefaction and Seismic Site Class

Liquefaction and Seismic Site Class

(OP)
I am looking for input on determining the seismic site class for a municipal water treatment facility.  The subsurface conditions consist of medium dense sand to 22 feet, clean & loose sand to 33 feet, dense to very dense sand below.  The groundwater is at 3 feet.

The loose sand between 22 to 33 feet is susceptable to liquefaction.  We are recommending ground improvement to ~10 feet beyond the building to mitigate the liquefaction potential.  

Following the ground improvement work, would the the corresponding IBC Seismic Site Class be D because the weighed average N value is 16 bpf?

RE: Liquefaction and Seismic Site Class

How did you determine that the 10-ft layer of loose sand is prone to liquifaction?

f-d

¡papá gordo ain’t no madre flaca!

RE: Liquefaction and Seismic Site Class

(OP)
The exploration program consisted of cased borings with STP testing.  Several lab grain size tests were performed to determine the percent fines.  A groundwater observation well had also been installed to measue the static water level.  We used this data in a liquefaction assessment following Youd et. al (2001) which is based on Seed and Idris.

RE: Liquefaction and Seismic Site Class

Without shear wave velocity measurements, site class D is appropriate.  If the soil improvement is extensive, the measured post improvement velocity may allow site class C.

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