The Properties of Dune Sand-Bentonite Mixtures for Use as Landfill Liners

摘要

This study investigated the properties of dune sand-bentonite mixtures. The physicalproperties of sand, bentonite and the mixtures were determined by performing Atterberg limits,specific gravity, grain size distribution, standard compaction, permeability, swelling,consolidation and shear strength. Also chemical analysis, cation exchange capacity (CEC),specific surface, X-ray diffraction (XRD) and scanning electron microscope (SEM) tests wereperformed. The liquid limit (LL) of bentonite was found to be 510 and the plasticity index (PI)was 439 with CEC of 110 meq/100g and specific surface of 625 m~2/g. Values of permeability ofdune sand-bentonite mixtures were found to decrease with the increase in bentonite content in apower form. Beyond 15% of bentonite the rate of decrease is small. The angle of internal friction(Φ) decreased with the increase in bentonite content from 45ο for a 5% bentonite to 29ο for 20%bentonite. However, the cohesion was increased from 0 to 66 kPa for the same bentonitecontents. The swelling pressure (and swelling percent) increased substantially with the increasein bentonite content specially when the bentonite content increased beyond 15%. Theconsolidation tests showed that the compressibility parameters (i.e. the compression index C_c andthe recompression index C_r) are practically constant with the increase in bentonite content up to15%. The compressibility of sand-bentonite mixtures in this range is small. The results ofscanning electron microscope (SEM) were used to explain the mechanisms behind the variationof the above engineering parameters.