671017.pdf

250

200

150

100

50

0

0 50 100 150 200 250

Matric suction sc=50kPa

Matric suction sc= 100kPa

Matric suction sc= 200kPa

Matric suction sc= 350kPa

Matric suction sc=500kPa

Fitting curves

Normal stress (kPa)

Shear

stren gt

h

(kPa)

(a) Shear strength envelops at drier than optimum water content

300

250

200

150

100

50

0

0 50 100 150 200 250

Matric suction sc=0kPa

Matric suction sc= 150kPa

Matric suction sc= 250kPa

Matric suction sc= 350kPa

Matric suction sc=500kPa

Fitting curves

Normal stress (kPa)

Shear

st

ren gt

h

(kPa)

(b) Shear strength envelops at wetter than optimum water content

Matric suction sc=0kPa

Matric suction sc= 150kPa

Matric suction sc= 350kPa

Matric suction sc=500kPa

Fitting curves

300

250

200

150

100

50

0

0 50 100 150 200 250

Normal stress (kPa)

Shear

stren gt

h

(kPa)

(c) Shear strength envelops at optimum water content

Figure 2: The curves of normal stress and shear strength at different initial water content state of soil (experimental data from Vanapalli
et al. [ 10 ]).

The suction stress can also be obtained from triaxial shear
tests according to Mohr-Coulomb criterion. The formula is
given as follows:

휎푆=−

휎 1 耠−푝푁

2 tan(휋/4 + 휑耠/2)tan휑耠

+

(휎耠 3 −푝푁)tan(휋/4 + 휑耠/2)

2 tan휑耠

+

푐耠

tan휑耠

,

(4)

where휎 1 耠and휎耠 3 are the major and minor principle stress,
respectively.

The new effective stress can be defined based on suction

stress as follows:

휎耠=(휎−푝푁)−휎푆, (5)

where휎耠is the effective stress and휎is the total stress. In

order to verify the expression of effective stress is reasonable,

the experimental data of shear strength or deformation tests

of unsaturated soils could be used.

Sandy-clay till was used to do shear strength test at

three types of water content state by Vanapalli et al. [ 10 ].

Shear failure envelops go upward drift with matric suction

increasing, which is shown inFigure 2(a).Simultaneously,

Figures2(a),2(b),and2(c)show that the shear strengths are