RESULTS AND DISCUSSION
4.1 EFFECT OF SAND CONTENT AND PARTICLE SIZE ON THE BEHAVIOR OF SAND-BENTONITE MIXTURES
4.1.3 CONSOLIDATION CHARACTERISTICS
4.1.3.8 Effect of bentonite content and initial compaction conditions on time required for 90% consolidation (t 90 )-Pressure relationship of sand-bentonite mixes
Figure 4.75 Effect of bentonite content on coefficient of volume change for sand- bentonite mixtures compacted at 5% wet of OMC-MDD, under a load of 784.8 kPa
In terms of their behavior with respect to initial compaction condition, bentonite content and sand type used in the mixture, a trend similar to those observed in case of FS-B1 and MS-B1 has been noticed.
Comparing compressibility behavior of FS-B1, MS-B1, FS-B2 and MS-B2 mixtures subjected to different consolidation pressures has shown an increase in mv values with increasing bentonite content and decreasing with increasing consolidation pressure as can be seen in Figs. 4.70 through Figs. 4.75.
4.1.3.8 Effect of bentonite content and initial compaction conditions on time
very clear distinction can be noticed in the exhibited t90 values indicating that B1 content in the mixtures plays a major role in consolidation phenomenon. As the B1 content in the mixture is decreasing, t90 was found to be decreasing. For any FS-B1 or MS-B1 mixture, t90 values were found to be increasing with initial mixing water content. FS-B1 mixtures exhibited relatively higher t90 values for all mix proportions and compaction conditions.
As the bentonite content in the mixture increases, voids in the sand skeleton are filled more effectively leading to a lower hydraulic conductivity, which in turn reflects in higher t90 values. With the increasing consolidation pressure, the voids and pathways that were available for flow to take place earlier are destroyed leading to a lower hydraulic conductivity and resulting in an increase in the duration needed for 90% consolidation.
The voids present in FS-B1 mixtures being relatively smaller in size compared to MS-B1 mixtures and less permeable, exhibiting relatively higher t90 values. For all compaction conditions, with their lowest hydraulic conductivities, 100% B1 mixtures exhibited highest t90 values compared to all sand-bentonite-1 mixtures.
Figure 4.76 Effect of bentonite content on t90-Pressure for FS-B1 samples compacted at 5% dry of OMC-MDD
0.01 0.1 1 10 100 1000
10 100 1000
Time for 90% consolidation (t90) (minutes)
Pressure (P) (kPa) 100% B1
50% B1 + 50% FS 40% B1 + 60% FS 30% B1 + 70% FS 20% B1 + 80% FS 10% B1 + 90% FS
Figure 4.77 Effect of bentonite content on t90-Pressure for FS-B1 samples compacted at OMC-MDD
Figure 4.78 Effect of bentonite content on t90-Pressure for FS-B1 samples compacted at 5% wet of OMC-MDD
0.01 0.1 1 10 100 1000
10 100 1000
Time for 90% consolidation (t90) (minutes)
Pressure (P) (kPa) 100% B1
50% B1 + 50% FS 40% B1 + 60% FS 30% B1 + 70% FS 20% B1 + 80% FS 10% B1 + 90% FS
0.01 0.1 1 10 100 1000
10 100 1000
Time for 90% consolidation (t90) (minutes)
Pressure (P) (kPa) 100% B1
50% B1 + 50% FS 40% B1 + 60% FS 30% B1 + 70% FS 20% B1 + 80% FS 10% B1 + 90% FS
Figure 4.79 Effect of bentonite content on t90-Pressure for MS-B1 samples compacted at 5% dry of OMC-MDD
Figure 4.80 Effect of bentonite content on t90-Pressure for MS-B1 samples compacted at OMC-MDD
0.01 0.1 1 10 100 1000
10 100 1000
Time for 90% consolidation (t90) (minutes)
Pressure (P) (kPa) 100% B1
50% B1 + 50% MS 40% B1 + 60% MS 30% B1 + 70% MS 20% B1 + 80% MS 10% B1 + 90% MS
0.01 0.1 1 10 100 1000
10 100 1000
Time for 90% consolidation (t90) (minutes)
Pressure (P) (kPa) 100% B1
50% B1 + 50% MS 40% B1 + 60% MS 30% B1 + 70% MS 20% B1 + 80% MS 10% B1 + 90% MS
Figure 4.81 Effect of bentonite content on t90-Pressure for MS-B1 samples compacted at 5% wet of OMC-MDD
4.1.3.8.2 Effect of bentonite content and compaction conditions on t90-Pressure relationship of FS-B2 and MS-B2 mixes
Influence of bentonite content, initial compaction conditions, consolidation pressure and sand type on the t90 of FS-B2 and MS-B2 mixtures is shown in Figs. 4.82 through Figs.
4.87. Trend similar to those exhibited by FS-B1 and MS-B1 mixtures were seen in the case of FS-B2 and MS-B2 mixtures. A clear influence of high swelling nature of B2 can be seen in the relatively higher t90 values exhibited by FS-B2 and MS-B2 mixtures for all compaction conditions.
Effect of bentonite content, compaction conditions, sand type and consolidation pressure on time for 90% consolidation (t90) can be seen in the Figs. 4.88 through Figs. 4.93. For all the compaction states and bentonite contents, mixtures with B2 exhibited higher t90
values some times as high as 10 times those demonstrated by B1 mixtures. Comparison of factors influencing t90 indicated that quality of bentonite has the most effect followed by bentonite content in the mixture. Influence of sand type on t90 can be seen in the mixtures with bentonite contents less than 30%, though very little.
0.01 0.1 1 10 100 1000
10 100 1000
Time for 90% consolidation (t90) (minutes)
Pressure (P) (kPa) 100% B1
50% B1 + 50% MS 40% B1 + 60% MS 30% B1 + 70% MS 20% B1 + 80% MS 10% B1 + 90% MS
Figure 4.82 Effect of bentonite content on t90-Pressure for FS-B2 samples compacted at 5% dry of OMC-MDD
Figure 4.83 Effect of bentonite content on t90-Pressure for FS-B2 samples compacted at OMC-MDD
0.1 1 10 100 1000
10 100 1000
Time for 90% consolidation (t90) (minutes)
Pressure (P) (kPa) 100% B2
50% B2 + 50% FS 40% B2 + 60% FS 30% B2 + 70% FS 20% B2 + 80% FS 10% B2 + 90% FS
0.1 1 10 100 1000
10 100 1000
Time for 90% consolidation (t90) (minutes)
Pressure (P) (kPa) 100% B2
50% B2 + 50% FS 40% B2 + 60% FS 30% B2 + 70% FS 20% B2 + 80% FS 10% B2 + 90% FS
Figure 4.84 Effect of bentonite content on t90-Pressure for FS-B2 samples compacted at 5% wet of OMC-MDD
Figure 4.85 Effect of bentonite content on t90-Pressure for MS-B2 samples compacted at 5% dry of OMC-MDD
0.1 1 10 100 1000
10 100 1000
Time for 90% consolidation (t90) (minutes)
Pressure (P) (kPa) 100% B2
50% B2 + 50% FS 40% B2 + 60% FS 30% B2 + 70% FS 20% B2 + 80% FS 10% B2 + 90% FS
0.1 1 10 100 1000
10 100 1000
Time for 90% consolidation (t90) (minutes)
Pressure (P) (kPa) 100% B2
50% B2 + 50% MS 40% B2 + 60% MS 30% B2 + 70% MS 20% B2 + 80% MS 10% B2 + 90% MS
Figure 4.86 Effect of bentonite content on t90-Pressure for MS-B2 samples compacted at OMC-MDD
Figure 4.87 Effect of bentonite content on t90-Pressure for MS-B2 samples compacted at 5% wet of OMC-MDD
0.1 1 10 100 1000
10 100 1000
Time for 90% consolidation (t90) (minutes)
Pressure (P) (kPa) 100% B2
50% B2 + 50% MS 40% B2 + 60% MS 30% B2 + 70% MS 20% B2 + 80% MS 10% B2 + 90% MS
0.1 1 10 100 1000
10 100 1000
Time for 90% consolidation (t90) (minutes)
Pressure (P) (kPa) 100% B2
50% B2 + 50% MS 40% B2 + 60% MS 30% B2 + 70% MS 20% B2 + 80% MS 10% B2 + 90% MS
Figure 4.88 Effect of bentonite content on t90 of sand-bentonite mixtures compacted at 5% dry of OMC-MDD, under a load of 196.2 kPa
Figure 4.89 Effect of bentonite content on t90 of sand-bentonite mixtures compacted at OMC-MDD, under a load of 196.2 kPa
0.01 0.1 1 10 100 1000
0 10 20 30 40 50
Time for 90% consolidation (t90) (minutes)
Bentonite content (%)
FSB1 MSB1
FSB2 MSB2
0.01 0.1 1 10 100 1000
0 10 20 30 40 50
Time for 90% consolidation (t90) (minutes)
Bentonite content (%)
FSB1 MSB1
FSB2 MSB2
Figure 4.90 Effect of bentonite content on t90 of sand-bentonite mixtures compacted at 5% wet of OMC-MDD, under a load of 196.2 kPa
Figure 4.91 Effect of bentonite content on t90 of sand-bentonite mixtures compacted at 5% dry of OMC-MDD, under a load of 784.8 kPa
0.01 0.1 1 10 100 1000
0 10 20 30 40 50
Time for 90% consolidation (t90) (minutes)
Bentonite content (%)
FSB1 MSB1
FSB1 MSB2
0.01 0.1 1 10 100 1000
0 10 20 30 40 50
Time for 90% consolidation (t90) (minutes)
Bentonite content (%)
FSB1 MSB1
FSB2 MSB2
Figure 4.92 Effect of bentonite content on t90 of sand-bentonite mixtures compacted at OMC-MDD, under a load of 784.8 kPa
Figure 4.93 Effect of bentonite content on t90 of sand-bentonite mixtures compacted at 5% wet of OMC-MDD, under a load of 784.8 kPa
0.01 0.1 1 10 100 1000
0 10 20 30 40 50
Time for 90% consolidation (t90) (minutes)
Bentonite content (%)
FSB1 MSB1
FSB2 MSB2
0.01 0.1 1 10 100 1000
0 10 20 30 40 50
Time for 90% consolidation (t90) (minutes)
Bentonite content (%)
FSB1 MSB1
FSB2 MSB2
Compressibility characteristics exhibited by FS-B1 and MS-B1 mixtures are summarized in Table 4.7. Compression index (cc) is defined as the slope of the virgin compression line in the e-log P curve. Compression index represents the ease of volume change when acted upon by a surcharge load. Observations indicated that compression index is increasing with bentonite content and the reason being the physical compression of diffuse double layers, formed around the bentonite particles upon hydration, is more in case of mixtures with high bentonite content when acted upon by increased surcharge load. Mixes made using medium sand exhibited relatively higher cc values indicating the ease of breakdown of relatively larger voids in the medium sand skeleton. The compressibility characteristics exhibited by sand-bentonite-2 mixtures are summarized in Table 4.8. Bentonite-2 being a high expansive soil resulted in relatively higher cc values.
Table 4.7 Summary of compression index results of FS-B1 and MS-B1 mixtures Mix proportion
(S:B)
Compression index (cc) Compaction condition
OMC 5% dry of OMC 5% wet of OMC Medium
Sand (MS)
0:100 0.506 0.326 0.380
50:50 0.400 0.235 0.365
60:40 0.385 0.273 0.356
70:30 0.093 0.143 0.093
80:20 0.057 0.089 0.060
90:10 0.064 0.136 0.065
Fine Sand (FS)
0:100 0.506 0.326 0.380
50:50 0.235 0.256 0.308
60:40 0.222 0.269 0.145
70:30 0.108 0.119 0.066
80:20 0.165 0.087 0.073
90:10 0.073 0.066 0.073
Table 4.8 Summary of compression index results of FS-B2 and MS-B2 mixtures Mix proportion
(S:B)
Compression index (cc) Compaction condition
OMC 5% dry of OMC 5% wet of OMC
Medium Sand (MS)
0:100 0.670 0.729 0.576
50:50 0.435 0.629 0.46
60:40 0.345 0.348 0.312
70:30 0.147 0.326 0.134
80:20 0.087 0.148 0.089
90:10 0.071 0.073 0.098
Fine Sand (FS)
0:100 0.670 0.729 0.576
50:50 0.515 0.502 0.419
60:40 0.371 0.522 0.483
70:30 0.120 0.264 0.167
80:20 0.106 0.179 0.068
90:10 0.064 0.073 0.073
4.1.4 FIELD EMISSION SCANNING ELECTRON MICROSCOPE (FESEM)