DESIGN SPECIFICATIONS FOR HIGHWAY BRIDGES - IISEE

4.5 Ground Type for Seismic Design
Grounds types in seismic design shall be classified, in principle, into those types
defined in Table 4.5.1, in accordance with the ground characteristic value TG calculated
from Equation (4.5.1). When the ground surface lies on the same level as the surface of
a bedrock in seismic design, the ground type shall be Type I.
TG
n
= 4
i1
H
V
si
i
・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・ (4.5.1)
where
TG : Characteristic value of ground (s)
Hi : Thickness of the i-th soil layer (m)
Vsi : Average shear elastic wave velocity of the i-th soil layer (m/s)
i : Number of the i-th soil layer from the ground surface when the ground is
classified into n layers from the ground surface to the surface of a bedrock in
seismic design
Table 4.5.1 Ground Types in Seismic Design
Ground Type Characteristic Value of Ground, TG (s)
Type I TG < 0.2
Type II 0.2 ≦TG < 0.6
Type III
0.6 ≦TG
4.6 Ground Surface to be considered in Seismic Design
Ground surface to be considered in seismic design shall generally be the ground surface
in the normal design. However, for sites of unstable soil layers whose seismic subgrade
reactions cannot be anticipated, the ground surface to be considered in seismic design
shall be appropriately assumed by taking the effects into account.
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