Shear Strength Applications in Plastic and Limit Equilibrium - Unsaturated Soil Mechanics in Engineering Practice - page 600

1.2

Best-fit line:
y w = 3.55 y d - 3.00

1.0

0.8

0.6

0.4

Goh (2012)
Han et al. (1996)
Rahardjo et al. (2004)

0.2

0.95 1.00 1.05 1.10 1.15 1.20

y d

Figure 12.15 Linear relationship between y w and y d (after Goh, 2012).

2.0

Best-fit line:
y = 0.542 b d ( n d / n w ) + 0.389
where:
n w = n parameter on
wetting curve

1.6

1.2

0.8

0.4

Goh (2011)
Han et al. (1995)
Rahardjo et al. (2004)

0.0

0.0 0.5 1.0 1.5 2.0 2.5

b d ( n d / n W )

Figure 12.16 Relationship between b w and b d (after Goh, 2012).

where: case where the residual suction is 200 kPa. In this case the

shear strength at residual suction is 96 kPa.

τ Sr = matric suction contribution to shear strength at

residual suction,

12.2.4.8 Vilar (2006) Estimation Shear Strength
Equation
Vilar (2006) proposed the use of a hyperbolic equation to
describe the shear strength versus soil suction relationship
for an unsaturated soil. Details of the Vilar (2006) model
are presented as a fitting model, but it is possible that with
further verification studies the model might be used for the
estimation of unsaturated shear strength.
The proposed model is based on the general shape of the
SWCC. It was assumed that the soil behaved as a saturated

ψ r = residual soil suction, and

ψ aev = suction at the air-entry value of the soil.

The φ and β terms are part of the correction factor that
reduces the shear strength as a result of desaturation of the
soil. A new term, τ Sr , is introduced into the shear strength
equation. The τ Sr term refers to the contribution of matric
suction to the shear strength at residual suction conditions,
ψ r . Figure 12.17 shows the meaning of the τ Sr term for the