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evaluated by Seed's approximate method. The additional ground motion or the additional
dynamic stress induced by the presence of building can be evaluated approximately with the
cone model well developed by Meek and Wolf in dynamics in recent years.
When the cone model is used, the shape of foundation should be equivalent to a fixed shape,
such as a circular footing, square footing or a strip footing. According to the cone model theory.
The two cones, one shear and another compression can confine the influence of structure.
Because the apex height of the shear cone and the apex height of the compression cone are
different, the total solution are divided into three zones as named as I, II and III, as shown in
Figure 1.
There are the additional vertical dynamic, static stresses and the additional dynamic shear
stress in zone I. There is only the additional dynamic shear stress in zone II. The stress
distribution is same as of the free ground in zone III. The procedure of evaluating seismic
liquefaction of subsoil of building using the simplified method proposed by Men et al as follows.
1. According to the cone model theory, the subsoil of building are divided into the three zones as
shown in Figure 1.
Determine the free field dynamic shear stress by using
Seed's simplified method.
2. Determine the additional shear stress and normal
stress of each zone by using the cone model.
3. Determine the total dynamic stress.
4. Use triaxial dynamic compression apparatus or
dynamic simple shear test devise to obtain the soil
liquefaction resistance r^for relevant point to be
considered.
5.Make a comparison between r d and 1 R for the every
point to see if that soil point may liquefy, as do in
Seed's simplified method.
Figure l.the cone models
The simplified method to evaluate the pore water pressure in subsoil
It is well known that volume of dry sand is changed under shear, i.e. the so-called dilatancy
under cyclic shear loading. For saturated sand this compression is gradually compensated by the
elastic rebound deformation of sand skeleton enabling thus the residual pore water pressure to
generated and the effective stress to decrease until ultimately the liquefaction occurs for certain
loading level with sufficient number of cycles
We neglect the inertial effect and the compressibility of pore water and sand grains here and then
following Martin et al (1975) 6 we can write out the pore pressure increment as
c s 2
A£... =c,(y-c,£,,,) + ——— ( 5 )
( 6 )
where e dv is the volume compression due to cyclic shear, i\£ dv ,i\G w the are increment of