CHAPTER 5 EXPERIMENTAL PROGRAM AND TEST RESULTS
5.4 SWCCs from Modified PPE
5.4.1 Controlled Radial Confinement Condition 5.4.1.1 SWCC for Sand
Figure 5.1 SWCC at Different Net Radial Confinement under Controlled Radial Confinement for Sand
Figure 5.1 shows a series of four SWCC tests performed on poorly-graded sand (SP) in the modified PPE device at fixed-boundary condition. Each test was performed at a different net radial confinement (N.R.C.), that is, (σr – ua) = 0, 1, 2.5, or 5 psi (0, 6.9, 17.25, or 34.5 kPa, respectively). It can be noticed the significant influence of N.R.C. on the shape and position of the SWCC. The SWCC is shifted rightward at higher net confinements. This can be attributed to a decrease in the average pore size (void ratio) of the soil mass as the N.R.C. is increased, despite the fact that all specimens featured similar moisture content and density prior to SWCC testing.
0 5 10 15 20 25
1 10 100 1000
Matric Suction, kPa
Gravimetric Moisture Content, % 0 kPa 6.9 kPa 17.25 kPa 34.5 kPa
5.4.1.2 SWCC for Clay
Figure 5.2 SWCC at Different Net Radial Confinement under Controlled Radial Confinement for Clay
Figure 5.2 shows a series of two SWCC tests performed on high plasticity clay (CH) in the modified PPE device at fixed-boundary condition. Each test was performed at a different net radial confinement (N.R.C.), that is, (σr – ua) = 1 or 5 psi (6.9 or 34.5 kPa, respectively). It can be noticed the significant influence of N.R.C.
on the shape and position of the SWCC. The initial SWCCs were started at similar moisture content. It can be stated that N.R.C. has no effect of saturation moisture content. The SWCC is shifted rightward at higher net confinements. This also can be attributed to a decrease in void ratio of the soil mass as the N.R.C. is increased, despite the fact that all specimens featured similar moisture content and density prior to SWCC testing.
20 21 22 23 24 25 26 27 28 29 30
1 10 100 1000
Matric Suction, kPa
Gravimetric Moisture Content, %
6.9 kPa 34.5 kPa
5.4.2 Constant K0 Stress State Condition 5.4.2.1 SWCC for Sand
Figure 5.3 SWCC at Different K0 under Constant K0 Condition for Sand
Figure 5.3 shows a series of four SWCC tests performed on poorly-graded sand (SP) in the modified PPE device at constant K0 condition. Each test was performed at a different constant K0, that is, (σr – ua)/σv = 0, 0.25, 0.625, and 1.25. It can be noticed that the influence of K0 on the shape and position of the SWCC is almost negligible. In this work, the selected range of the experimental variables was intended to reproduce in-situ stress states within a pavement or shallow foundation system (less than 5-psi confinement). Therefore, it is expected that higher levels of stress (more than 10-psi confinement) will have a considerable effect on the SWCC response of SP soils.
0 5 10 15 20 25
1 10 100 1000
Matric Suction, kPa
Gravimetric Moisture Content, % Ko=0
Ko=0.25 Ko=0.625 Ko=1.25
5.4.2.2 SWCC for Clay
Figure 5.4 SWCC at Different K0 under Constant K0 Condition for Clay
Figure 5.4 shows a series of four SWCC tests performed on high plasticity clay (CH) in the modified PPE device at constant K0 condition. Each test was performed at a different constant K0, that is, (σr – ua)/σv = 0, 0.25, 0.625, and 1.25. It can be noticed that the considerable influence of K0 on the shape and position of the SWCC is negligible.
Again, the selected range of the experimental variables was intended to reproduce in-situ stress states within a pavement or shallow foundation system (less than 5-psi confinement). It is expected that higher levels of stress (more than 10-psi confinement) will have a considerable effect on the SWCC response of CH soils.
20 22 24 26 28 30
1 10 100 1000
Matric Suction, kPa
Gravimetric Moisture Content, %
Ko=0 Ko=0.25 Ko=0.625 Ko=1.25
5.4.3 Variable K0 Stress State Condition 5.4.3.1 SWCC for Sand
Figure 5.5 SWCC at Different Initial K0 Stress State under Variable Suction Dependent K0 Condition for Sand
Figure 5.5 shows a series of four SWCC tests performed on poorly-graded sand (SP) in the modified PPE device under variable suction dependent K0 stress state condition. Each test was performed at different three initial K0 stress states, that is, (σr – ua)/σv = 0, 0.5, and 1. Likewise, the suction-dependent (variable) K0
stress state was found to exert no significant influence on the SWCC response of SP soils under controlled K0 stress state condition. This can be explained by the possible fact that the average pore size (void ratio) of the soil mass, for the range of stress levels applied, did not experience major variations during SWCC testing.
0 5 10 15 20 25
1 10 100 1000
Matric Suction, kPa
Gravimetric Moisture Content, % Ko=1
Ko=0.5 Ko=0.25
5.4.3.2 SWCC for Clay
Figure 5.6 SWCC at Different Initial K0 Stress State under Variable Suction Dependent K0 Condition for Clay
Figure 5.6 shows a series of four SWCC tests performed on high plasticity clay (CH) in the modified PPE device under variable suction dependent K0 condition.
Each test was performed at different initial K0 stress state, that is, (σr – ua)/σv = 0, 0.5, and 1. Again, suction-dependent (variable) K0 stress state was found to exert no significant influence on the SWCC response of CH soils under controlled K0 stress state condition. This can also be explained by the possible fact that the average pore size of the soil mass, for the range of stress levels applied, did not experience major variations during SWCC testing.
20 22 24 26 28 30 32
1 10 100 1000
Matric Suction, kPa
Gravimetric Moisture Content, %
Ko=1 Ko=0.5 Ko=0.25