Solving Stress-Deformation Problems with Unsaturated Soils - Unsaturated Soil Mechanics in Engineering Practice - page 748

10,000

Natural Regina clay
Compacted Regina clay
Eston clay

1,000

3 : 1

2 : 1

1 : 1

100

10

10 100 1,000

Uncorrected swelling pressure, P s (kPa)

Figure 14.21 Change to measured swelling pressure as result of applying correction for sam-
pling disturbance.

each succeeding series of tests. Figures 14.23-14.27 show
the swelling pressure measurements and compression
curves as the soil was compacted to lower densities while
having initial higher water contents. Figures 14.24-14.27
also show the slope of the rebound curves. The slope of the
rebound curves, C s , was approximately 0.12. A line drawn
through the void ratios corresponding to “after-free-swell”
conditions under various surcharge loads results in a
slightly steeper rebound curve.
Singhal (2010) performed a similar set of compara-
tive swell pressure tests on expansive clay in Arizona
(Fig. 14.28). The soil had a plastic index of 52. The
load-back swell pressure is the pressure required to return
the soil to its initial void ratio after the soil has swelled
under its initial surcharge pressure. The load-back swelling
pressures ranged from 410 to 480 kPa.

Table 14.3 Volume-Mass Properties and Swelling
Pressures for Series of Oedometer Tests on Regina Clay

Swelling

Void Dry Unit Water Pressure

Series Ratio Weight, kN/m 3 Content, % Range, kPa

1 0.67 16.0 22 1570-2160

2 0.79 14.9 27 640-980

3 0.94 13.8 32 200-350

4 1.05 13.0 37 120-180

5 1.29 11.7 45 30-80

6 1.48 10.8 51 15-30

Source: From Gilchrist (1963).