Symbols Used
CHAPTER 5 EFFECT OF HEAVY METALS ON BEHAVIOUR OF BENTONITES
5.2. RESULTS AND DISCUSSIONS 1 Atterberg limits
5.2.7. Consolidation characteristics 1. Void ratio-pressure relationship
5.2.7.5. Time for 90% of consolidation (t 90 )
Figures 5.31 and 5.32 show the relationship between pressure and time to complete 90% of the consolidation (t90). The plots indicate that with an increase in the consolidation pressure the t90 for the sample increases. For both the bentonites, t90 decreases with an increase in the concentration of heavy metal ions in the pore fluid. For any given concentration and pressure, a higher value of t90 was observed for Bentonite-B in comparison to Bentonite-A.
With increase in the pressure from 9.8 kPa to 784.5 kPa the t90 for Bentonite-B permeated with 100 ppm of Pb2+ increased from 23.1 minutes to 918.1 minutes; whereas, it increased only from 0.3 minutes to 408.0 minutes for Bentonite-A. Similarly, the t90 for Bentonite-B permeated with 1000 ppm of Pb2+ increased from 37.1 minutes to 875.2 minutes; whereas, it increased only from 0.8 minutes to 361.3 minutes for Bentonite-A
Figure 5.31 Plot between the time for 90% of consolidation and consolidation pressures of Bentonite-A and -B at 100 ppm concentration of heavy metals
0 200 400 600 800 1000 1200
1 10 100 1000
Time for 90% consolidation,t90 (minutes)
Pressure (kPa) Water
100 ppm Pb2+
100 ppm Zn2+
100 ppm Cu2+
____ Bentonite-A ... Bentonite-B
Figure 5.32 Plot between the time for 90% of consolidation and consolidation pressures of Bentonite-A and -B at 1000 ppm concentration of heavy metals
Figure 5.33 shows the relationship between the liquid limit and the time taken to complete 90% of consolidation (t90) at the consolidation pressures of 19.6 kPa, 196.1 kPa and 784.5 kPa. It was observed that irrespective of the consolidation pressure, the t90 increased with the increase in the liquid limit of the bentonite. For Bentonite-A, samples compacted at OMC-MDD and in the presence of Zn2+, t90 increased from 3.1 minutes to 462.2 minutes with an increase in liquid limit from 165.1 % to 218.0 %; however for Bentonite-B, t90
increased from 49.0 minutes to 922.1 minutes with an increase in liquid limit from 279.1 % to 560.0 %. For Bentonite-A, in presence of Cu2+ the t90 increased from 3.0 minutes to 412.1 minutes with an increase in liquid limit from 163.0 % to 218.0 %; however for Bentonite-B, t90 increased from 50.4 minutes to 918.1 minutes with an increase in liquid limit from 264.2 % to 560.0 %. Similar trend for cv was observed for the bentonites in presence of Pb2+ solutions. The plots also show the effect of liquid limit on t90 was significant at high consolidation pressure.
0 200 400 600 800 1000
1 10 100 1000
Time for 90% consolidation,t90 (minutes)
Pressure (kPa) Water
1000 ppm Pb2+
1000 ppm Zn2+
1000 ppm Cu2+
____ Bentonite-A ... Bentonite-B
0 200 400 600 800 1000 1200
0 10 20 30 40
Time for 90% consolidation,t90 (minutes)
Free swelling (mL/2g)
19.6 kPa 196.1 kPa 784.5 kPa ____ Bentonite-A ... Bentonite-B
0 200 400 600 800 1000 1200
0 10 20 30 40
Free swelling (mL/2g)
19.6 kPa 196.1 kPa 784.5 kPa ____ Bentonite-A ... Bentonite-B
0 200 400 600 800 1000 1200
0 10 20 30 40
Time for 90% consolidation,t90 (minutes)
Free swelling (mL/2g)
19.6 kPa 196.1 kPa 784.5 kPa ____ Bentonite-A ... Bentonite-B
0 200 400 600 800 1000 1200
0 10 20 30 40
Free swelling (mL/2g)
19.6 kPa 196.1 kPa 784.5 kPa ____ Bentonite-A ... Bentonite-B
A. At OMC-MDD in presence of Pb2+
solution
B. At 5% dry of OMC-MDD in presence of Pb2+ solution
C. At OMC-MDD in presence of Zn2+ solution D. At 5% dry of OMC-MDD in presence of Zn2+ solution
0
200 400 600 800 1000 1200
0 10 20 30 40
Time for 90% consolidation,t90 (minutes)
Free swelling (mL/2g)
19.6 kPa 196.1 kPa 784.5 kPa
0 200 400 600 800 1000 1200
0 10 20 30 40
Free swelling (mL/2g)
19.6 kPa 196.1 kPa 784.5 kPa
0 200 400 600 800 1000 1200
0 200 400 600
Time for 90% consolidation,t90 (minutes)
Liquid limit (%)
19.6 kPa 196.1 kPa 784.5 kPa
0 200 400 600 800 1000 1200
0 200 400 600
Liquid limit (%)
19.6 kPa 196.1 kPa 784.5 kPa ____ Bentonite-A ... Bentonite-B
E. At OMC-MDD in presence of Cu2+ solution F. At 5% dry of OMC-MDD in presence of Cu2+ solution
A. At OMC-MDD in presence of Pb2+ solution B. At 5% dry of OMC-MDD in presence of Pb2+ solution
Figure 5.33 Plot between time for 90% consolidation and free swelling for Bentonite-A and -B for different heavy metals at different initial compaction condition
____ Bentonite-A ... Bentonite-B
____ Bentonite-A ... Bentonite-B
____ Bentonite-A ... Bentonite-B
0 200 400 600 800 1000 1200
0 200 400 600
Time for 90% consolidation,t90 (minutes)
Liquid limit (%)
19.6 kPa 196.1 kPa 784.5 kPa ____ Bentonite-A ... Bentonite-B
0 200 400 600 800 1000 1200
0 200 400 600
Liquid limit (%)
19.6 kPa 196.1 kPa 784.5 kPa ____ Bentonite-A ... Bentonite-B
0 200 400 600 800 1000
0 200 400 600
Time for 90% consolidation,t90 (minutes)
Liquid limit (%)
19.6 kPa 196.1 kPa 784.5 kPa
____ Bentonite-A ... Bentonite-B
0 200 400 600 800 1000
0 200 400 600
Liquid limit (%)
19.6 kPa 196.1 kPa 784.5 kPa
____ Bentonite-A ... Bentonite-B
C. At OMC-MDD in presence of Zn2+ solution D. At 5% dry of OMC-MDD in presence of Zn2+ solution
E. At OMC-MDD in presence of Cu2+ solution F. At 5% dry of OMC-MDD in presence of Cu2+ solution
Figure 5.34 Plot between time for 90% consolidation and the liquid limit for Bentonite-A and –B for different heavy metals at different initial compaction condition
Figure 5.34 shows that the t90 for the bentonites increased with the increase in the free swelling capacity of the bentonites. For Bentonite-A, samples compacted at OMC-MDD and in the presence of Zn2+, t90 increased from 3.0 minutes to 462.2 minutes with an increase in free swelling from 6 mL/2g to 17 mL/2g; but for Bentonite-B, t90 increased from 47.0 minutes to 918.1 minutes with an increase in free swelling from 8 mL/2 g to 34 mL/2g. Similarly for Bentonite-A in presence of Cu2+, t90 increased from 1.4 minutes to 412.1 minutes with an increase in free swelling from 7 mL/2g to 17 mL/2g; but for Bentonite-B, t90 increased from 48.0 minutes to 918.1 minutes with an increase in free swelling from 6 mL/2g to 34 mL/2g.
For Bentonite-A, samples compacted at 5% dry of OMC-MDD and in presence of Zn2+, t90
increased from 1.2 minutes to 441.0 minutes with an increase in free swelling from 6 mL/2g to 17 mL/2g; but for Bentonite-B, t90 increased from 30.0 minutes to 806.0 minutes with an increase in free swelling from 8.5 mL/2g to 34 mL/2g. Similarly for Bentonite-A, in presence of Cu2+ t90 increased from 1.4 minutes to 441.0 minutes with an increase in free swelling from 7 mL/2g to 17 mL/2g but for Bentonite-B, t90 increased from 24.0 minutes to 807.1 minutes with an increase in free swelling from 6 mL/2g to 34 mL/2g. Samples compacted at dry of OMC has lower t90 values than samples compacted at OMC.