Hard rock with measured shear wave velocity, vs > 5,000 ft/sec (1500 m/s)
Rock with 2,500 ft/sec < vs < 5,000 ft/sec (760 m/s < vs <1500 m/s)
Very dense soil and soft rock with 1,200 ft/sec < vs < 2,500 ft/sec (360 m/s < vs <
760 m/s) or with either N > 50 or su >2,000 psf (100 kPa)
Stiff soil with 600 ft/sec < vs < 1,200 ft/sec (180 m/s < vs < 360 m/s) or with either
15< N < 50 or 1,000 psf < su < 2,000 psf (50 kPa < su < 100 kPa)
A soil profile with vs < 600 ft/sec (180 m/s) or with either N < 15, su < 1,000 psf, or
any profile with more than 10 ft (3 m) of soft clay defined as soil with PI >20, w > 40
percent, and su <500 psf (25 kPa).
Soils requiring site-specific evaluations:
Soil vulnerable to potential failure or collapse under seismic loading such as
liquefiable soils; quick and highly sensitive clays; and collapsible, weakly
2.Peats and/or highly organic clays (H > 10 ft [3 m] of peat and/or highly
organic clay where H = thickness of soil).
3.Very high plasticity clays (H > 25 ft [8 m] with PI > 75).
Very thick soft/medium stiff clays (H > 120 ft [36 m]).
Note: vs is shear wave velocity; N is Standard Penetration Resistance (ASTM D1586-84), not to exceed
100 blows/ft as directly measured in the field without corrections; su is undrained shear strength, not to
exceed 5,000 psf (250 kPa) (ASTM D2166-91 or D2850-87). vs , N , and su are average values for the
respective parameters for the top 100 feet of the site profile. Refer to FEMA 302 for the procedure to
obtain average values for vs , N , and su .
Exception: When the soil properties are not known in sufficient detail to determine the Site Class, Site
Class D shall be used. Site Classes E or F need not be assumed unless the authority having jurisdiction