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A desorption technique was employed to evaluate chemisorption of ammonia by clays under moist conditions. In equilibria involving ammonia, all factors favoring volatilization losses of gaseous ammonia would undoubtedly exert an influence on the ultimate equilibria which are reached. Investigation of the relationship between pH and ammonia equilibria in soils revealed that an increase in the concentration of ammonium ions, applied as ammonium sulfate, stimulated ammonia losses from fine-textured soils at pH's ranging from 4.5 to 7.1. Ammonia volatilization was directly related to the initial pH of the soil and increased with an increase in pH. It was postulated that ammonia may be volatilized, even from acid soils, due to the equilibrium NH₄⁺ + OH⁻ ⇌ NH₃ + H₂O. By using initial concentrations of ammonium ions from ammonium sulfate applied, initial pH of an aqueous suspension of the soil and a value K_b = 1.80 x 10⁻⁵, values of ammonia losses were predicted. The linear relationship found between predicted and measured amounts of ammonia losses from acid as well as neutral soils, was interpreted as evidence of the existence of the proposed volatilization mechanism in soils. In attempting to evaluate the characteristics of ammonia retention by homo-ionic bentonites and kaolinites under moist conditions, it was found that base-saturated clays did not chemisorb ammonia in a fashion which could be described by Langmuir's adsorption isotherms. The S-shaped curves did not necessarily reflect polymolecular sorption. In strong contrast, chemisorption of ammonia by Al-saturated clays, followed Langmuir's equation almost perfectly. Evaluation of the inverse values of the differential slopes of two straight line segments obtained in the desorption isotherms corresponded closely to values obtained for the permanent charge (CEC) and the total charge (total CEC) developed at a specific pH higher than 6 respectively. It was shown that if sufficient ammonia is applied, exchangeable Al⁺⁺⁺ of Al-compounds may be precipitated as Al(OH)₃. An attempt to evaluate pseudo-equilibrium constants for aluminum-clay ammonia equilibria by using Langmuir's adsorption equation, was unsatisfactory. Chemical kinetic studies indicated that ammonia volatilization reactions could be described by a fast reaction and a slow reaction. The slow reaction represented chemisorption of ammonia on the permanent charge exchange sites. Extrapolation of the slow reaction to zero time yielded values corresponding closely to the CEC permanent charge. Investigation of the effects of CO₂, the NH₄⁺ concentration is increased, resulting in more effective replacement of basic cations for "permanent charge" exchange spots. The lower pH and higher effective NH₄⁺ concentration resulted in higher retention of NH₄⁺ in Na⁺- and K⁺-clays. The most striking retention of NH₄⁺ was obtained in Mg- and particularly in Ca-bentonites. It is believed that the Ca and Mg ions, exchanged by NH₄⁺ ions, are effectively removed from the soil solution as a result of the precipitation of these compounds which are sufficiently insoluble to ensure conservation of ammonia as chemisorbed ammonium ions. / Ph. D.

The main purpose behind this thesis was to study the variations of strength in a soil after it had been stabilized with various percentages of lime, cement, and combinations of the two. In both cases where the additives were added separately to the soil, the percentages used were 5 and 10 per cent by dry weight of soil. In the additive combination study, lime-cement percentage additions were 2-3, 3-2, 4-6, and 6-4 by dry weight of soil. The first two percentages, when added together, amount to 5 per cent stabilizing agent, while the latter two total 10 per cent. Since these two totals were the same as those used in the separate lime and cement studies, an analysis of strength changes when lime, cement, and lime-cement combinations were added to the soil could be made. Strength studies which were made consisted of unconfined compression immediately after compaction and after a four-day curing period in a 100 per cent humidity curing room. Atterberg limit tests were also run at the various percentages of additive. The laboratory test results indicate: 1. For cured specimens containing a stabilizing agent, the greatest four-day strengths will occur at or above OMC, in most cases. This may not always be true in the case of cement, since moisture condition is not as significant in cement stabilization as it is in other types. 2. Control of moisture at or near OMC during field compaction appears to be much more important in lime stabilization than in cement stabilization if maximum strengths are to develop. This statement is supported by a statistical analysis which was performed on the strength data. 3. The variation of' the lime-cement percentage trom 6-4 to 4-6 has no effect on four-day cured strengths. / M.S.

M.S.

The use of tensile reinforcement to increase the tensile strength and shear strength of soils has lead to many new applications of reinforced soil. The use of such reinforcing in embankments and foundations over weak soils is one of the most recent applications of this technology. The studies conducted were concerned with the development of and application of analytical techniques to reinforced soil foundations and embankments over weak soils. A finite element computer program was modified for application to reinforced soil structures, including consolidation behavior of the foundation soil. Plane strain and axisymmetric versions of the program were developed and a membrane element developed which has radial stiffness but no flexural stiffness. The applicability of the program was verified by comparing analytical results to case histories of reinforced embankments and to model studies of reinforced foundations. A simplified procedure for computing the bearing capacity of reinforced sand over weak clay was developed which is more general than those previously available. Good agreement with available experimental results was obtained, providing preliminary verification of the procedure. Extensive analyses were made of a reinforced embankment successfully constructed with no sign of distress, and of two reinforced embankments constructed to failure. These analyses showed that good agreement can be obtained between measured and calculated reinforcement forces, settlements, and pore pressures for both working and failure conditions. The analyses further show that the use of the finite element method and limit equilibrium analyses provide an effective approach for the design of reinforced embankments on weak foundations. / Ph. D. / incomplete_metadata

Swelling attributable to intracrystalline water adsorption by montmorillonite (MT) and vermiculite (VR) saturated with cations which limit interlayer expansion were calculated as the product of one-half the change in interlayer spacing determined by x-ray diffraction and the difference between total surface area taken as 800 m²/g and external crystal surface area measured by N₂ gas adsorption. Swelling directly attributable to osmotic adsorption was calculated as the product of external surface area and theoretical double layer thickness. In homoionic, monomineralic systems of Ca- and Al-MT and Na-, Ca- and Al-VR, intracrystalline expansion accounted for 60, 70, 21, 56 and 44%, respectively, of total expansion during saturated vapor-wetting and 15, 50, 4, 12 and 13% during submersion in 0.01 N electrolyte solutions. Osmotic adsorption of these systems accounted for < 10% of the expansion on submersion in all cases. Dry, static compaction of Ca-MT resulted in an increase in expansion with increasing initial density which was not explained by changes in predicted osmotic or intracrystalline expansion. This was attributed to expansion caused by gaseous pressures developing ahead of advancing wetting fronts. An inverse relationship was found between pore size and swelling caused by entrapped air pressures. Slow wetting ameliorated this expansion by allowing dissipation of entrapped air. Relaxation of crystal strains during wetting was also implicated as contributing to expansion. Electron microscopy revealed crystal strain decreased in the order: Na-MT > Ca-HT > Al-MT > Na-VR ≃ Ca-VR ≃ Al-VR. Greater expansion by freeze-dried than oven-dried Ca-MT was explained by greater crystal strain observed in the former clay. Greater strain broadening of the (060) x-ray diffraction peak was observed for the freeze-dried clay and its mean b-dimension was slightly smaller than the oven-dried clay. Crystal strain relaxation is suggested to explain the relationship between b-dimension and swelling reported in the literature. Predicted osmotic expansion for two soils was greater than in the pure clay systems and intracrystalline expansion smaller, due to a greater ratio of external to internal surface area in the soils. Osmotic adsorption accounted for 30-70% of the soil swelling during submersion in 0.0lM electrolyte solutions, while intracrystalline expansion accounted for < 10%. The magnitude of swelling due to entrapped air pressures was evaluated from the difference between expansion of atmospheric pressure-wet and vacuum-wet clods. This component accounted for 10-60% of the expansion of undisturbed and compacted samples during the second cycle of wetting from the air-dry state, but did not appear to be directly related to pore size. Changes in structure accompanying air-drying appeared to enhance expansion, especially for the high MT Iredell soil. It was suggested that this may be the result of increases in crystal strain during drying. / Ph. D.