Journal of Geotechnical and Geoenvironmental Engineering

The effectiveness of fly ash use in the stabilization of organic soils and the factors that are likely to affect the degree of stabilization were studied. Unconfined compression and resilient modulus tests were conducted on organic soil–fly ash mixtures and untreated soil specimens. The unconfined compressive strength of organic soils can be increased using fly ash, but the amount of increase depends on the type of soil and characteristics of the fly ash. Resilient moduli of the slightly organic and organic soils can also be significantly improved. The increases in strength and stiffness are attributed primarily to cementing caused by pozzolanic reactions, although the reduction in water content resulting from the addition of dry fly ash solid also contributes to strength gain. The pozzolonic effect appears to diminish as the water content decreases. The significant characteristics of fly ash that affect the increase in unconfined compressive strength and resilient modulus include CaO content and $\mathrm{CaO}/{\mathrm{SiO}}_2$ ratio [or $\mathrm{CaO}/({\mathrm{SiO}}_2+{\mathrm{Al}}_2{\mathrm{O}}_3)$ ratio]. Soil organic content is a detrimental characteristic for stabilization. Increase in organic content of soil indicates that strength of the soil–fly ash mixture decreases exponentially. For most of the soil–fly ash mixtures tested, unconfined compressive strength and resilient modulus increased when fly ash percentage was increased.

This paper presents an experimental study of the effect of porosity and particle size on the hydraulic conductivity and thermal conductivity of sand-sized crushed granite particles with diameters ranging from 0.08–10 mm. The results show that the hydraulic conductivity varies with particle size and porosity, but thermal conductivity varies primarily with porosity. Estimating methods found in the literature are used in an attempt to predict the measured hydraulic and thermal conductivities of the crushed granite materials. The results show that the hydraulic conductivity model of Chapuis generally yields accurate estimated values for $d_{10}^2{n}^3/(1-n{)}^2$ larger than $0.01{\mathrm{mm}}^2$. Below this critical point, the estimating method progressively yields larger values of hydraulic conductivity. A new set of empirical parameters are proposed to extend the use of this method to crushed granite materials at low $d_{10}^2{n}^3/(1-n{)}^2$ values. It is also shown that predicted thermal conductivity values obtained with the Côté and Konrad model agree well with the experimental data. Issues regarding the extension of the models to coarser materials are discussed.

The output from an earth pressure cell (EPC) is usually related to the normal stress in soil through fluid calibration, where a known pressure is applied to the EPC and the output is recorded. However, distribution of normal stress within a soil is not uniform, and the EPC is not an ideal membrane—bending stiffness affects the response. These factors complicate the performance of the EPC. A calibration procedure for an EPC is reviewed, and it is shown that these controversial sensors can provide an accurate measure of average normal stress if calibrated in soil at a given density. In addition, a soil-structure interaction model is proposed to explain why soil calibration is necessary.

In this work, oedometer tests were used to examine the effects of ethanol-gasoline blends on the consolidation characteristics of a kaolinitic soil from northwestern Spain. As the fraction of ethanol in blends increases, the equivalent liquid limit of soil decreases, showing a dividing point for blends containing about 85% of ethanol. By means of a database of compression indexes of remolded clayey soils mixed with differing kinds of alcohol and petroleum hydrocarbon contaminants, a multivariable model for estimating the compression index of the contaminated soil is presented, on the basis of the virgin compression index, normalized liquid limit, and normalized pore fluid viscosity. The model is valid only for percentages of active clays up to 10–15% in weight in kaolinitic soil. The authors would like to encourage others to further validate and refine the approach, which may be useful for preliminary estimation of the compression index of contaminated soils, reducing operators’ risk of inhaling vapors released by the ethanol-gasoline blends while performing the test and also reducing damage to conventional oedometer equipment.

Analytical solutions are presented for analyzing volatile organic compound (VOC) diffusion through intact composite landfill liners for two scenarios with boundary conditions at the base of either a VOC concentration of zero or a VOC mass flux of zero. A time-dependent concentration top boundary condition is included in the presented analytical solutions to model typical variations of VOC concentration in the leachate over time. The presented solutions are verified against alternative numerical solutions and applied to analyze dichloromethane diffusion through a composite liner. The analytical solutions are found to provide useful predictions of VOC concentration and mass flux for the design of composite liners. VOC concentrations and fluxes at the base of the composite liner at 30 years predicted by consideration of representative transient variation in leachate concentration, for an example problem, are nearly half of those when a constant leachate concentration assumed.