Environmental Engineering Reference
In-Depth Information
Measured gravimetric water content,
w
(%)
0
18
20
22
24
26
28
30
32
34
0.5
1.0
1.5
2.0
2.5
3.0
Figure 16.24
Distribution of in situ gravimetric water content measured on August 21, 1961.
The case history is presented as a two-dimensional anal-
ysis to illustrate the prediction of heave in expansive soils.
Estimation of the initial matric suction condition is presented
in Table 16.6 and shown graphically in Fig. 16.23. A straight
line can be used to represent the distribution of the initial
matric suction with depth.
The initial degrees of saturation and volumetric water con-
tents were calculated from the measured initial densities of
the soil. The measured water contents and degrees of satura-
tion at various values of matric suction were used to estimate
the SWCC. The Fredlund and Xing (1994) equation for a
SWCC (Eq. 16.82) in terms of volumetric water content
showed the following fitting parameters:
θ
s
=
(1994) fitting parameters for the degree-of-saturation data
were
a
f
0
.
7 (Fig. 16.25).
A coefficient-of-permeability function for compacted Regina
clay was measured by Shuai (1996). The coefficient-of-
permeability function was described using the Leong and
Rahardjo (1997) equation SWCC 16.83 and is presented in
Fig. 16.26.
The analysis examines a cross section A-A through the
building (see Fig. 16.22). The lower boundary is selected at
2.3m depth since the test results showed that there would be
no tendency for swelling below this depth (Fig. 16.23).
The geometry and boundary conditions for the seepage
analysis are shown in Fig. 16.27. It was observed that water
leaked from the water line along a 2-m length of the line.
It was assumed that the initial suction conditions did not
change outside the edges of the concrete slab or below the
lower boundary. A moisture flux equal to zero was specified
elsewhere along the boundaries.
Matric suction conditions were predicted for various
elapsed times (i.e., 5, 20, 50, and 100 days and at steady-state
conditions).
=
300 kPa,
n
f
=
0
.
5, and
m
f
=
49
.
3%,
a
f
=
300 kPa,
n
f
=
0
.
6, and
m
f
=
0
.
7. The Fredlund and Xing
Table 16.6 Estimation of Initial Matric Suction from
Corrected Swelling Pressure
At Various Depths
Variable
0.69 m
1.34 m
2.20 m
16.8.4 Computer Simulations of Slab-on-Grade
with Shallow Strip Footings
Deformation of the slab took into consideration the applied
building loads and the reduction in suction due to wetting.
Deformations in the soil mass due to the slab loading were
assumed to be immediate while deformations due to wetting
were time dependent. Figure 16.28 shows the stress path fol-
lowed in the analysis. The stress-deformation analysis was
first performed to calculate the displacements and induced
stresses related to the loading of the slab and building. The
deformations due to changes in matric suction were then pre-
dicted for various elapsed times using soil suction profiles
obtained from the seepage analysis.
The stress-deformation analysis was also performed for
cases where the pore-water pressures go to zero as well as
Overburden pressure
(σ
y
−
13.03
25.30
41.54
u
a
)
initial
(kPa)
Initial void ratio
e
0
0.927
0.985
0.974
Corrected swelling
pressure
P
s
(kPa)
490
325
81
Gravimetric water
content
w
(%)
25
29
31
Degree of saturation
S
(%)
76
83
90
Volumetric water
content
θ
(%)
36.6
41.2
44.3
Estimated field suction
(u
a
−
627
361
44
u
w
)
initial
(kPa)
Note
:
S
=
wG
s
/e
and
θ
=
wG
s
/(
1
+
e)
.
Search WWH ::
Custom Search