Stress-Deformation Analysis for Unsaturated Soils - Unsaturated Soil Mechanics in Engineering Practice - page 713

Table 13.3 Characteristics of Three Soils from Research Literature

Soil name Kaolin Jossigny Silt Regina Clay

Soil-water characteristic curve from initially slurried w sat 0.830 (83%) 0.467 (46.7%) 1.057 (105.7%)

10 9 10 33

a 1 . 9 × 71,000 1 . 0 ×

b 2.527 1.404 9.838

w r 0.049 (4.9%) 0.064 (6.4%) 0.131 (13.1%)

Characteristics of hysteretic SWCCs D SL 0.6 0.6 N/A

R SL 2 1.5 1.5

β 0.05 0.05 N/A

C c

Compression indices 0.37 0.22 0.74

C s

0.085 0.045 0.134

C cd 0 0 0

Specific gravity G s 2.54 2.55 2.83

Pore shape parameter η 2 2 2

Compressibility of dry pore M N/A N/A N/A

100

Measured data (preconsolidated at 25 kPa)
Measured data (initially slurried)
Best-fitted for initially slurried
Measured data (preconsolidated at 400 kPa)
Predicted curve

90

80

70

60

50

40

30

20

10

0

1 10 100 1000 10,000 100,000 10 6

Soil suction, kPa

Figure 13.55 Measured, best-fit, and predicted SWCCs for Regina clay (data from Fredlund,
1964).

content at stress states corresponding to a wide variety of
loading-unloading and drying-wetting stress paths; (ii) tak-
ing into account the hysteretic nature of the SWCC; and
(iii) predicting both swelling and collapsible behavior of an
unsaturated soil.
The model can simulate volume-mass constitutive rela-
tionships that are stress path dependent. The model utilizes
a hysteresis model for the SWCC that makes use of two
one-dimensional pore-size distributions. The model intro-
duced two new parameters: the pore shape parameter η and
the compressibility of the dry pore parameter, m . Further
research on these two soil parameters would be useful since
it will likely lead to improved estimation procedures for the
new soil parameters.

13.7 FORMULATION OF PARTIAL
DIFFERENTIAL EQUATIONS FOR
STRESS-DEFORMATION IN UNSATURATED SOILS

The emphasis thus far in this chapter has been on the for-
mulation of suitable volume-mass constitutive relations for
an unsaturated soil. Let us now consider the formulation of
PDEs for a REV. The derived partial differential equations are
applicable for solving stress-deformation problems involving
unsaturated soils. The emphasis is on the calculation of over-
all volume changes in unsaturated soils (i.e., soil structure
volume changes).
The derivation of partial differential equations required
to solve stress-deformation problems starts with satisfying