B. R. Phanikumar

Landfill liners blended with industrial by-product seems to outperform the conventional liners. This paper presents the influence of sawdust (SD) admixed with bentonite and locally available lateritic soil on consistency limits, free swell index (FSI), compaction characteristics, unconfined compressive strength (UCS), hydraulic conductivity and leachate characteristics. SD content was varied as 10%, 15% and 20%. Diesel oil contaminants (DOC) and deionised water (DIW) were used as the test fluids. From the test results, consistency limits, FSI, maximum dry density, leachate concentration of heavy metals and UCS decreased, whereas optimum moisture content and hydraulic conductivity increased with increasing sawdust content. Furthermore, the energy-dispersive X-ray spectrometer revealed the absence of calcium in the blends which have resulted in poor cementation and decreased the UCS. X-ray diffraction showed that the presence of cellulose in sawdust and montmorillonite in bentonite adsorb the heavy metals in DOC. Based on the test results, 15% Saw dust content in the blends proves to be the optimum in retaining the heavy metal concentrations, improving the geotechnical properties and qualifying as a landfill liner material.

Structures found in expansive soils are subjected to heave and downward movement when they absorb water and lose water to the atmosphere, respectively. The upward and downward movements of structures built on the expansive clay strata are controlled through various treatment methods such as chemical stabilisation. As these clay strata are subjected to stresses due to superstructures, an understanding of their load-carrying capacity in the light of changing moisture content is required to assess this behaviour. This paper presents the heave and load-settlement behaviour of a remoulded expansive clay bed stabilised with varied amounts of lime, cement, fly ash and ground granulated blast furnace slag (GGBS). A series of laboratory-scale plate load tests were conducted on the beds of chemically stabilised clay compacted at the respective OMC and MDD. The plate load tests were conducted in two series: one on the as-compacted beds of the blends, and the other on the saturated beds of the blends to compare their stress-settlement behaviour. The amount of heave and the rate of heave were also monitored during the process of saturation. Chemically stabilised expansive clay beds reflected improved load-settlement behaviour in both the as-compacted and the saturated states.

This paper presents the results of laboratory-scale swell-shrink tests performed in an oedometer on an expansive soil stabilised by calcium carbide residue-fly ash (CCR-FA) columns. The expansive soil used in this study had a swell potential of 11.56%. The CCR-FA columns (3 mm in diameter) were seven in number diametrically arranged in the oedometer. In another series of tests, the expansive soil was directly mixed with the CCR-FA blends. The 3-D volumetric shrinkage of the samples was measured using digital image analysis in five swell-shrink cycles. The results were compared with the shrinkage measured manually. The impact of this treatment on soil morphology was interpreted using SEM. A significant reduction of 62% was observed in swell potential when CCR-FA columns were used at the CCR:FA ratio of 20:80. Uneven swelling patterns for some of the cycles indicate partial loss of cementation. The results of the 3-D volumetric shrinkage indicated only partial success of the treatment in preventing shrinkage. The digital image analysis estimated slightly higher 3-D volumetric shrinkage than that observed through manual measurement. SEM demonstrated the observed changes in soil morphology due to swell-shrink cycles. Further studies would be required to conclude on prevention of shrinkage.

This note presents the effect of lime, cement, fly ash and ground granulated blast furnace slag (GGBS) on free swell index (FSI), liquid limit (LL), plasticity index (PI), compaction characteristics, hydraulic conductivity ( k ) and strength characteristics of an expansive soil. The effect of the above chemicals on California bearing ratio (CBR) is also presented. Lime content was 0, 1, 2, 4 and 6% and the amounts of other additives were 0, 5, 10, 15 and 20% by dry weight of the soil. FSI, LL and PI decreased significantly with increasing additive contents. Compaction characteristics also improved with increasing additive contents. Strength characteristics showed improvement at higher additive contents especially at higher curing periods. CBR (determined in soaked condition) also increased significantly with increasing additive contents.

Granular pile-anchor (GPA) technique is an innovative tension-resistant foundation technique which can effectively ward off the dual swell–shrink problem posed by expansive clays. The other tension-resistant foundation techniques are drilled piers, belled piers and under-reamed piles. Laboratory scale model studies and field scale experiments on GPAs revealed that swelling of expansive clay beds could be effectively controlled by GPA technique. This paper presents results obtained from laboratory scale model studies on GPA-reinforced expansive clay beds subjected to alternate cycles of wetting and drying. Swelling and shrinkage of the clay beds were monitored for three wetting–drying cycles (N) spanning a time period of 300 days. The clay beds were reinforced with varying number of GPAs (n = 0, 1, 2 and 3). Swelling (mm) and shrinkage (mm) of the clay beds in a given wetting–drying cycle decreased with increasing number of GPAs. Further, swelling (mm) and shrinkage (mm) significantly decreased with increasing number of wetting–drying cycles (N) also. For a given number of GPAs (n), swelling and shrinkage decreased with increase in depth from the top of the clay bed too.

Expansive soil subgrades, which are subjected to dual swell-shrink problem consequent upon absorption and evaporation of water, need to be improved by chemical stabilization or compacted cushion or geosynthetic reinforcement in order that pavements constructed over them are even, stable and safe. This paper presents extensive experimental data on plasticity, free swell index (FSI) and compaction characteristics of a highly swelling expansive clay stabilized with varying silica fume contents. In another series of tests on a laterite soil to be used as a cushion over the expansive clay subgrade, plasticity properties, compaction characteristics and strength characteristics were determined at varied silica fume contents. Further, CBR of the expansive clay subgrade was determined in the laboratory stabilizing it with varied silica fume contents and providing a cushion of 50 mm thickness of silica fume-stabilized lateritic soil. Liquid limit (LL), plasticity index (PI) and free swell index (FSI) of the expansive clay decreased with increasing silica fume contents. The compaction and strength characteristics of both the soils improved with silica fume stabilization. The CBR of the expansive clay provided with silica fume-stabilized cushion improved significantly.