Abstract:
Clay rich soils used as liners and covers for containment of industrial waste and other materials, are compacted wet of optimum with a view to minimize the hydraulic conductivity of the liners and covers. Resultantly the shrinkage potential of the clayey soil increases in arid / semi arid regions where liners and covers are subjected to seasonal drying.
The use cement, sand and waste / recycled polythene to reduce the shrinkage potential of the compacted high plastic clay liner was studied. The experimental study comprised a number of volume shrinkage, permeability and unconfined compression tests on samples of compacted high plastic clay (PI: 31 or more) with various compositions of clay, sand, cement and polythene chips by percent of weight. Variation of volume shrinkage potential, i.e.,the governing parameter, unconfined compression strength and permeability were analyzed with samples compacted at dry of optimum moisture content (OMC), at OMC and wet of OMC at constant compactive effort (modified compactive effort). Variation of volume shrinkage potential was analyzed with varying amount of sand, cement and varying sizes and proportion of polythene chips also. Samples of composite material having varying proportion of sand, cement and polythene chips were also analyzed for volume shrinkage potential and test results of samples having desired volume were analyzed for variation of permeability and unconfined compression strength.
Evaluation of test data of specimen compacted at varying moisture content showed that volume shrinkage potential increased with increase in molding water content, exceeding the desired limit whilst resultant reduction in unconfined compression
Strength and permeability remained within permissible limits, To reduce the volume shrinkage potential, each of sand, cement and polythene with varying proportion were added to clay but results showed no reduction in volume shrinkage potential. Polythene was found unsuitable to be used for reducing volume shrinkage potential as increase in its size and proportion would make compaction and its uniform distribution over entire sample difficult and would reduce bounding between soil particles. Either sand or cement alone also did not produce effective results.
Tests performed on composite material gave better results and showed a positive trend towards reduction of volume shrinkage potential and samples having 30 % sand,6 % cement with varying amount of polythene chips i.e., 0.5,0.75,1.0 %. Showed reduction of volume shrinkage potential to average of 3.5 %. Results of unconfined compression strength and permeability tests performed on these three combinations were well within limits i.e., more than 360 Kpa and less than 0.0785 x 10-9 m/s respectively.
