EARTHQUAKE-INDUCED SETTLEMENT - Geotechnical Earthquake Engineering - page 185

Note in Fig. 7.1 that the volumetric strain can also be calculated for clean sand that has
a factor of safety against liquefaction in excess of 1.0. For FS L greater than 1.0 but less than
2.0, the contraction of the soil structure during the earthquake shaking results in excess pore
water pressures that will dissipate and cause a smaller amount of settlement. At FS L equal
to or greater than 2.0, Fig. 7.1 indicates that the volumetric strain will be essentially equal
to zero. This is because for FS L higher than 2.0, only small values of excess pore water pres-
sures u e will be generated during the earthquake shaking (i.e., see Fig. 5.15).
Method by Tokimatsu and Seed (1984, 1987). Figure 7.2 shows a chart developed by
Tokimatsu and Seed (1984, 1987) that can be used to estimate the ground surface settle-
ment of saturated clean sands. The solid lines in Fig. 7.2 represent the volumetric strain for
liquefied soil (i.e., factor of safety against liquefaction less than or equal to 1.0). Note that
the solid line labeled 1 percent volumetric strain in Fig. 7.2 is similar to the dividing line in
Fig. 6.6 between liquefiable and nonliquefiable clean sand.
The dashed lines in Fig. 7.2 represent the volumetric strain for a condition where excess
pore water pressures are generated during the earthquake, but the ground shaking is not
sufficient to cause liquefaction (i.e., FS 1.0). This is similar to the data in Fig. 7.1, in that
FIGURE 7.2 Chart for estimating the ground surface settlement of clean sand for fac-
tor of safety against liquefaction less than or equal to 1.0 (solid lines) and greater than
1.0 (dashed lines). To use this figure, the cyclic stress ratio from Eq. (6.6) and the ( N 1 ) 60
value from Eq. (5.2) must be determined. ( Reproduced from Kramer 1996, originally
developed by Tokimatsu and Seed 1984. )