Symbols Used
CHAPTER 3 MATERIALS AND METHODS
4.2. RESULTS AND DISCUSSION 1. Atterberg limits
4.2.5. Swelling pressure
swelling from 6 mL/2g to 34 mL/2g the swelling potential increased from 24.5 % to 48.4
%. Similarly for Bentonite-A, in presence of CaCl2 solution and compacted at OMC-MDD, with an increase in free swelling from 5 mL/2g to 17 mL/2g the swelling potential increased from 13.7 % to 21.1 %, however for Bentonite-B, with an increase in the free swelling from 5 mL/2g to 34 mL/2g the swelling potential increased from 21.4 % to 48.4 %.
Similarly, Fig. 4.10 shows that the swelling potential increased with an increase in liquid limit of bentonite. The increase in swelling potential was more prominent for Bentonite-B in comparison to Bentonite-A. For Bentonite-A, in presence of NaCl and compacted at OMC-MDD, with an increase in liquid limit from 94.9 % to 218.0 % the swelling potential increased from 13.5 % to 21.1 %, but for Bentonite-B, with an increase in liquid limit from 112.0 % to 560.0 % the swelling potential increased from 24.5 % to 48.4 %. Similarly for Bentonite-A, in presence of CaCl2 and compacted at OMC-MDD, with an increase in liquid limit from 90.0 % to 218.0 %, the swelling potential increased from 13.7 % to 21.1
%; but for Bentonite-B, with an increase in liquid limit from 107.0 % to 560.0 %, the swelling potential increased from 21.4 % to 48.4 %.
the swelling pressure of the bentonite decreased with the increase in the salt concentration.
Similar to the liquid limit, free swelling and swelling potential, the decrease in the swelling pressure with the increase in salt concentration was different for different range of concentration. For Bentonite-A, the swelling pressure decreased significantly with the increase in the concentration from 0 to 0.1 N of both NaCl and CaCl2 solution, where it decreased from 267.7 kPa for 0 N concentrations to 186.3 kPa and 176.5 kPa for 0.1 N concentration of NaCl and CaCl2, respectively. A further increase in the concentration from 0.1 to 1 N decreased the swelling pressure marginally to 157.9 kPa and 156.9 kPa for NaCl and CaCl2, respectively. Similarly, for Bentonite-B the decrease in swelling pressure was relatively higher for increase in concentration from 0 to 0.1 N. For the Bentonite-B compacted at OMC-MDD and permeated with NaCl solution, the swelling pressure decreased marginally from 708.0 kPa to 686.4 kPa due to increase in the concentration from 0 to 0.01 N, however, it decreased significantly from 686.4 kPa to 418.7 kPa and again from 418.7 kPa to 300.0 kPa when the concentration increased from 0.01 to 0.1 N and 0.1 to 1 N, respectively.
In comparison to the CaCl2 solution, for any given concentration a higher value of swelling pressure was observed for NaCl solution. This can be attributed to a higher value of diffuse double layer thickness in NaCl solution in comparison to CaCl2 solution of same concentration. However, the difference in swelling pressure was decreased with the increase in the concentration.
A comparison between the two bentonites showed that the salt has a significant effect on the swelling pressure of Bentonite-B in comparison to Bentonite-A. The swelling pressure of Bentonite-B, which has a high liquid limit, high SSA, CEC and ESP, decreased significantly due to increase in the salt concentration. A comparison of the initial compaction condition on the swelling pressure shows that initial water content has a
marginal effect on the swelling pressure irrespective of the permeating liquid. Similar observation was also made by Holtz and Gibbs (1956), Seed et al. (1962) and Chen (1975).
Figure 4.11 Effect of salt concentrations on swelling pressures of Bentonite-A and -B at different compaction conditions
4.2.5.1. Relationship of the swelling pressure with free swelling and liquid limit
From Fig. 4.12 and 4.13 it can be observed that swelling pressure of the bentonite increased with an increase in the free swelling and liquid limit value. For Bentonite-A, in presence of NaCl and compacted at OMC-MDD, with an increase in free swelling from 5 mL/2g to 17 mL/2g, the swelling pressure increased from 157.9 kPa to 267.7 kPa, however for Bentonite-B, with an increase in free swelling from 6 mL/2g to 34 mL/2g, swelling pressure increased from 300.0 kPa to 708.0 kPa. Similarly for Bentonite-A, in presence of CaCl2 and compacted at OMC-MDD, with an increase in free swelling from 5 mL/2g to 17 mL/2g, the swelling pressure increased from 156.9 kPa to 267.7 kPa; but for Bentonite-B,
100 200 300 400 500 600 700 800
0.001 0.01 0.1 1
Swelling pressure (kPa)
Salt concentration (N)
Bentonite A-NaCl Bentonite A-CaCl2 Bentonite B-NaCl Bentonite B-CaCl2
DI water
... 5% dry of OMC-MDD ____ OMC-MDD
Figure 4.12 Swelling pressure versus free swelling plot of Bentonite-A and-B
Figure 4.13 Swelling pressure versus liquid limit plot of Bentonite-A and-B 100
200 300 400 500 600 700 800
0 10 20 30 40
Swelling pressure (kPa)
Free swelling (mL/2g)
Bentonite A-NaCl Bentonite A-CaCl2 Bentonite B-NaCl Bentonite B-CaCl2 DI water
... 5% dry of OMC-MDD ____ OMC-MDD
100 200 300 400 500 600 700 800
0 100 200 300 400 500 600
Swelling pressure (kPa)
Liquid limit (%)
Bentonite A-NaCl Bentonite A-CaCl2 Bentonite B-NaCl Bentonite B-CaCl2
DI water
... 5% dry of OMC-MDD ____ OMC-MDD
with an increase in free swelling from 5 mL/2g to 34 mL/2g, swelling pressure increased from 273.5 kPa to 708.0 kPa. Similarly for Bentonite-A, in presence of NaCl and compacted at OMC-MDD, with an increase in liquid limit from 94.9 % to 218.0 % the swelling pressure increased from 157.9 kPa to 267.7 kPa, however, for Bentonite-B, with an increase in liquid limit from 112.0 % to 560.0 %, swelling pressure increased from 300.0 kPa to 708.0 kPa. For the Bentonite-A samples saturated with CaCl2 solution and compacted at OMC-MDD, with an increase in liquid limit from 90.0 % to 218.0 %, the swelling pressure increased from 156.9 kPa to 267.7 kPa, whereas, for Bentonite-B, with an increase in liquid limit from 107.0 % to 560.0 %, swelling pressure increased from 273.5 kPa to 708.0 kPa.