Evaluation of red soil-bentonite mixtures for compacted clay liners

Compacted clay liners are an integral part of the waste landfills,which are provided to contain the leachate within the landfills and protect the surrounding environment.Generally,locally available natural soils are used for the construction of compacted clay liners if they satisfy the design criteria.However,not all soils in their natural state satisfy all the design criteria for the liner materials.Thus,there is a definite need to modify the locally available natural soils by blending with bentonite to meet the required design criteria for the liners.In view of this,the present study evaluates the suitability of an Indian red soil enhanced with bentonite as a liner material.To achieve this,a series of experiments were carried out using locally available red soil and bentonite.First,the suitability of the red soil was evaluated as a liner material.The experimental results showed that the red soil met all the selection criteria stipulated by the Environmental Protection Agencies(EPAs)for the liners except the hydraulic conductivity criterion.Therefore,the red soil was mixed with bentonite contents of 10%,20%and 30%,and the red soil-bentonite mixtures were evaluated for their suitability for liners in their compacted state.Further,as the liners in the arid and semi-arid regions are subjected to moisture variations due to seasonal moisture fluctuations and other factors,the red soil-bentonite mixtures were subjected to wetdry cycles,and their suitability was evaluated after wet-dry cycles.The experimental results revealed that all the red soil-bentonite mixtures met the stipulated EPA criteria for the liners in the as-compacted state.However,the red soil-bentonite mixtures with 20%and 30%bentonite contents only satisfied the hydraulic conductivity requirement even after wet-dry cycles.The experimental findings were supplemented with the microstructural insights captured through digital camera images,scanning electron microscopy(SEM),and mercury intrusion porosimetry(MIP)studies.

Structural,volumetric and water retention behaviors of a compacted clay upon saline intrusion and freeze-thaw cycles

This study investigates the evolution of the structural,volumetric and water retention behaviors of a compacted clay during soaking and desiccation considering the influences of freeze-thaw(FT)cycles and saline intrusion.Compacted specimens were subjected to different FT cycles and then submerged in NaCl solution with different concentrations to facilitate the saline intrusion and measure the swelling behaviors.Shrinkage curve and filter paper tests were thereafter performed to reveal the clay’s volumetric and water-retention characteristics during desiccation.Mercury intrusion porosimetry and field emission scanning electron microscopy tests were conducted to observe the evolution of the clay’s microstructure.Experimental results show that the clay’s micropores decrease and macropores increase after FT cycles,which is associated with the migration of water,growth of ice crystals,and development of FT-induced cracks during FT cycles.Similar observations were obtained from specimens after the saline intrusion,which is attributed to the osmotic and osmotically-induced consolidation.FT-induced cracks significantly reduce the clay’s swelling and shrinkage potentials.FT cycles result in the shrinkage of micropores which leads to a reduction in the water retention capacity in the low suction range(capillary regime).The salinization suppresses the swelling of the clay and prolongs its primary and secondary swelling stages.The shrinkage potential initially increases and then decreases with increasing saline concentration.Salinization has significant influences on the osmotic suction and thus alters the clay’s water-retention curves in terms of total suction.It demonstrates little impact on the clay’s water-retention curves in terms of matric suction.

Behavior of compacted clay-concrete interface

Tests of interface between compacted clay and concrete were conducted systematically using interface simple shear test apparatus.The samples,having same dry density with different water content ratio,were prepared.Two types of concrete with different surface roughness,i.e.,relatively smooth and relatively rough surface roughness,were also prepared.The main objectives of this paper are to show the effect of water content,normal stress and rough surface on the shear stress-shear displacement relationship of clay-concrete interface.The following were concluded in this study:1)the interface shear sliding dominates the interface shear displacement behavior for both cases of relatively rough and smooth concrete surface except when the clay water content is greater than 16%for the case of rough concrete surface where the shear failure occurs in the body of the clay sample;2)the results of interface shear strength obtained by direct shear test were different from that of simple shear test for the case of rough concrete surface;3)two types of interface failure mechanism may change each other with different water content ratio;4)the interface shear strength increases with increasing water content ratio especially for the case of clay-rough concrete surface interface.