Stress-Deformation Analysis for Unsaturated Soils - Unsaturated Soil Mechanics in Engineering Practice - page 689

e 0

Loading curve
Unloading curve

a t

a ts

Figure 13.20 Typical shrinking and swelling curves for soil sub-
jected to suction changes.

Net normal stress s - u a

Figure 13.18 Typical compression curve for a saturated soil plot-
ted using an arithmetic scale.

Figure 13.21 Soil structure constitutive surface for monotonic
unloading of stable-structured soil.

The same procedure used to obtain the deformation coeffi-
cients for the loading surfaces can also be used to obtain the
deformation coefficients for the unloading surface. The only
difference lies in the direction of deformation for unload-
ing. The a ts coefficient can be computed from curve A s in
Fig. 13.21. The curve represents the rebound curve on the
saturation plane. The b ts coefficient in Fig. 13.22 is calcu-
lated as a ts divided by G s .
Curve B s in Fig. 13.22 represents the wetting portion of
the SWCC. The b ms coefficient can be obtained from the
wetting curve. The a ms

Figure 13.19 Typical SWCC showing drying and wetting of soil.

the compression loading curve for a saturated soil plotted
against the logarithm of effective stress has a compression
index C c , whereas the unloading curve has a swelling
index C s . The void ratio and water content surfaces for
monotonic unloading are illustrated in Figs. 13.21 and 13.22,
respectively. Coefficients of compressibility corresponding
to the unloading surfaces can be further subscripted with an
s (i.e., a ts , a ms , b ts , and b ms ).

coefficient is then calculated from