P. V. Sivapullaiah

Swelling Pressure of Clays

Experiments by three methods to determine the swelling pressure of clays showed that the conventional consolidation test gives an upper bound value, the method of equilibrium void ratios for various consolidation pressures gives the least value, and tests by the constant volume method give intermediate values. However there is no definite relationship between the three methods. The paper also shows that time effects involved in conducting the tests and the effect of stress path are both significant. Time versus swelling, and to a greater extent, time versus pressure relations can be represented by a rectangular hyperbola, which can be used to predict the ultimate swelling and the swelling pressure, respectively. Tests with varying initial conditions of molding moisture content and density have exhibited a unique relationship between swelling pressure and the initial dry density for black cotton soil. This result is in line with the osmotic pressure theory. The molding water content has marginal effect on the swelling pressure.

Mini compaction test apparatus for fine grained soils

The standard and modified Proctor compaction tests are devised to establish dry unit weight-water content relationships for a soil under controlled conditions, such as compactive effort, water content, etc. This paper presents a mini compaction apparatus primarily for use in fine grained soils, which requires only about 1/10th volume of soil needed for the standard and modified Proctor test. Additionally, the time and effort involved in carrying out the compaction test is much less. Also, the compacted soil sample, after trimming, can be used for strength tests.

Liquid limit of soil mixtures

The liquid limit test is one of the most widely used tests in the soil enginering practice. Several prroperties, including mechanical properties (for example, compressive index), have correlations with the liquid limit. In this paper detailed investigations of the liquid limit of soil mixtures have been carried out using bentonite, kaolinite, sand (coarse grained, fine grained, rounded and angular shaped), and silts. Based on the results obtained, it has been shown that the liquid limits of soil mixtures are not governed by the linear law of mxtures. While the shape of the sand was not found to influence the liquid limit, the size of the sand particles had a definite influence. Liquid limit obtained by the cone method is lesser than the limit obtained by using the Casagrande apparatus. A good relationship exists between the results of these two methods. A procedure for obtaining the liquid limit of low plastic soil has been suggested. (Author) been suggested. (Author)

Pozzolanic fly ash as a hydraulic barrier in land fills

The liner plays an important role in controlling migration of contaminants present in the leachate in waste containment systems such as land fills and impoundments. Although questions have been raised about the performance of clay liners, they are increasingly used singly or as double liners in disposal sites. Though the clay liners possess many advantages such as low permeability and large attenuative capacity, they also possess high shrinkage potential and hence can crack under unsaturated conditions causing instability and increase in leakage rates. Further, the permeability of the clay linear can increase due to clay–pollutant interaction. This study examines the potential of pozzolanic fly ash as a hydraulic barrier in land fill. The behaviour of three different types of fly ashes, showing a range of physical properties and chemical composition from three different sources are reported in the study. Geotechnical properties, needed to evaluate the use of fly ashes as barriers, such as shrinkage, compaction, permeability, consolidation and strength characteristics are reported. The results show that fly ashes possess low shrinkage and hence do not crack. Compacted fly ashes undergo very little volume changes. They also show that pozzolanic fly ashes develop good strength properties with time. Pozzolanic fly ashes containing sufficient lime develop strength even without addition of lime. Non-pozzolanic fly ashes do not develop strength even on addition of lime. Fly ashes generally consist of silt size particles and consequently possess high permeability. However, pozzolanic fly ashes with lime exhibit low permeability on curing because of the formation of gelatinous compounds which block the pores. Thus, pozzolanic fly ashes appear to be promising for construction of liners to contain alkaline leachate.

Role of Gypsum in the Strength Development of Fly Ashes with Lime

The strength of fly ash mixture often needs to be enhanced for its better utilization in geotechnical and environmental applications. Many fly ashes often improve their strength with lime but may not meet the requirements. Gypsum, which reduces the lime leachability, further improves the strength. An attempt is made in this paper to study the effect of gypsum on the strength development of two Class F fly ashes with different lime contents after curing them for different periods. The sustainability of improved strength has been examined after soaking the cured specimens in water and with different leachates containing heavy-metal ions. The strength of both the fly ashes investigated improved markedly up to a particular amount of the lime content, which can be taken as optimum lime content, and thereafter the improvement is gradual. The improvement in strength at higher lime contents continues for a longer period (even up to 180 days). Gypsum accelerates the gain in strength for lime-stabilized fly ashes, particularly in the initial curing periods at about optimum lime content. At high lime contents gypsum attributes very high strength after curing for long periods mainly due to the alteration of fly ash lime reaction compounds. Gypsum not only improves the reduction in the loss of strength due to soaking even at low curing periods but also improves the durability of stabilized fly ashes due to repeated cycles of wetting and drying.

Technical Note Reactive silica and strength of fly ashes

The use of fly ash in geotechnical engineering depends greatly on its pozzolanic reactivity. Though many factors influence the reactivity of fly ash it is well recognized that reactive silica and lime content play a major role. A new, accurate and reliable method for the determination of reactive silica content of fly ash has been established. The reactive silica content, obtained as acid soluble silica in about 2 to 3 N hydrochloric acid, is found to correlate well with unconfined compressive strength of fly ashes. The reactive silica content of fly ash is also important in the stabilization of soils using fly ash.

Optimization of Lime Content for Fly Ash

Abundant quantities of fly ash have been produced by thermal power plants situated ail over the world. Many applications of fly ash depend upon its pozzolanic reactivity. This reactivity depends upon many factors, including lime content. Many fly ashes show marked improvement with the addition of lime. However, for every fly ash, there is an optimum lime content for its maximum reactivity. There is no well-established simple test to determine the optimum lime content. In this paper an attempt is made to use a simple physical and physico chemical test to determine the optimum lime content. The principle behind the use of a pH test, liquid limit test, and free swell index test to determine the optimum lime content has been explained. All the methods predict nearly the same optimum lime content and correlate well with that determined by the strength test.

Improvement of Strength of Expansive Soil with Waste Granulated Blast Furnace Slag

Utilization of industrial waste materials in the improvement of problematic soils is a cost efficient and also environmental friendly method in the sense that it helps in reducing disposal problems caused by the various industrial wastes. The main objective of the present study is to improve various engineering properties of the soil by using waste material Ground Granulated Blast Furnace Slag (GGBS) as an alternative to lime or cement, so as to make it capable of taking more loads from the foundation structures. This paper reports the findings of laboratory tests carried out on local Indian expansive black cotton soil with GGBS mixed with the expansive soil in different proportions. The specimens compacted to their respective Proctor’s optimum moisture content and dry density (which varied from mixture to mixture) were cured for a period of 7, 14 and 28 days and their unconfined compression strengths were determined. It is observed that the strength improvement depends on the amount of GGBS used and the effect of curing period is less pronounced. Further it was shown that the initial tangent modulus values generally increases with increase in GGBS content.

Gypsum treated fly ash as a liner for waste disposal facilities

Fly ash has potential application in the construction of base liners for waste containment facilities. While most of the fly ashes improve in the strength with curing, the ranges of permeabilities they attain may often not meet the basic requirement of a liner material. An attempt has been made in the present context to reduce the hydraulic conductivity by adding lime content up to 10% to two selected samples of class F fly ashes. The use of gypsum, which is known to accelerate the unconfined compressive strength by increasing the lime reactivity, has been investigated in further improving the hydraulic conductivity. Hydraulic conductivities of the compacted specimens have been determined in the laboratory using the falling head method. It has been observed that the addition of gypsum reduces the hydraulic conductivity of the lime treated fly ashes. The reduction in the hydraulic conductivity of the samples containing gypsum is significantly more for samples with high amounts of lime contents (as high as 1000 times) than those fly ashes with lower amounts of lime. However there is a relatively more increase in the strengths of the samples with the inclusion of gypsum to the fly ashes at lower lime contents. This is due to the fact that excess lime added to fly ash is not effectively converted into pozzolanic compounds. Even the presence of gypsum is observed not to activate these reactions with excess lime. On the other hand the higher amount of lime in the presence of sulphate is observed to produce more cementitious compounds which block the pores in the fly ash. The consequent reduction in the hydraulic conductivity of fly ash would be beneficial in reducing the leachability of trace elements present in the fly ash when used as a base liner.

Properties of Fly Ash as Hydraulic Barrier

This study examines the suitability of pozzolanic fly ash as a hydraulic barrier and the use of bentonite to enhance geotechnical properties of fly ash. The behavior of fly ash is studied not only with water but also with different pore fluids, such as acid, alkali, salts, and neutral organic fluid to assess its chemical compatibility. While some geotechnical properties of fly ash meet the requirements of liner material, the disadvantage of using of fly ash alone is that it has a low cation exchange capacity and high hydraulic conductivity. The compressibility of fly ash reduces with alkaline solution but increases with acidic solutions. While alkaline or neutral inorganic solutions do not affect the hydraulic conductivity of fly ash, the addition of dilute acid increases the hydraulic conductivity. Addition of bentonite improves the geotechnical properties of fly ash such as cation exchange capacity, shrinkage and volume change behavior, etc. Fly ash-bentonite mixtures possess low shrinkage and hence do not crack. Compacted fly ash-bentonite mixtures undergo very little volume changes under various stress conditions. The hydraulic conductivity of fly ash is reduced after amendment with bentonite. Though the unconfined compressive strength of the mixture is lower than that of fly ash alone, the fly ash-bentonite mixture still possesses good strength. The compressibility of fly ash bentonite mixtures are lower with different pore fluids studied than with water. The hydraulic conductivity of fly ash-bentonite mixtures are slightly higher in different pore fluids studied than with water.