Characteristics of Compacted Fly Ash as a Transitional Soil

Cohesive and non-cohesive soils show a number of properties typical of a given category. Cohesive soils are characterized by cohesion, and the properties of compacted soils closely depend on moisture at compaction. However, many researchers have found the existence of so-called mixed or transitional soils. Compacted transitional soils, macroscopically recognized as non-cohesive, are characterized by mechanical properties and hydraulic conductivity which are strictly dependent on the moisture content at compaction. The aim of this work is to show the influence of the content of fine particles in fly ash on the variation of California Bearing Ratio (CBR) values as a parameter strictly dependent on initial compaction. The CBR values were interpreted in terms of moisture at compaction, void ratio and intergranular void ratio. Three different research samples were selected with fine contents of 45%, 55% and 70%; all samples corresponded in terms of grading with sandy silt. Fly ash containing only non-plastic fines behaved as cohesive soils despite the lack of plasticity. The CBR values decreased with increasing moisture at compaction or void ratio. The CBR values, plotted as a function of the intergranular void ratio, have lower penetration resistance together with fine content.

Assessing Relations Between Electrical and Geotechnical Properties of Sand-Clay Mixtures Using Jonscher Fractal Power Law Model

The geotechnical properties of unconsolidated geo-materials such as soils are influenced by modifications of their micro-structure, texture, mineralogy, water content and imposed effective stress levels. Fundamental relations between the characteristic electrical parameters describing the electrical responses soils based on a fractal power law model with scaling properties, and parameters influencing their geotechnical behavior are investigated. Low frequency electrical conductivity laboratory measurements were performed on sand and clay mixtures subjected to varying effective stress levels with concurrent measurements of their geotechnical properties. The conductivity spectra of the mixtures were described using a Jonscher fractal power law model characterized with three characteristic parameters, the dc conductivity ( σ dc ), the characteristic frequency ( f c ) and an exponent ( n). Changes in effective stress, water content, clay content, and other engineering properties of the mixture such as dry density, porosity, pore size and intergranular void ratio are discussed with respect to changes in the electrical parameters. The dc conductivity and characteristic frequency decrease with an increase in effective stress levels. The exponent, however, has the opposite behavior and increases with an increase in effective stress. As the water content increases, σ dc and f c increase while n decreases for all mixtures. With increasing stress levels, the average pore size of the mixtures decreases which results in a decrease in σ dc and f c but an increase in the values of the exponent. An increase in dry density of the mixtures leads to a decrease in σ dc and f c whilst n increases. Both σ dc and f c increase with increase in the intergranular void ratio of the mixture whilst the exponent values decrease with an increase in the intergranular void ratio. This study serves as a contribution to our quest in utilizing electrical geophysical methods, to assess and monitor non-invasively, the geotechnical properties of the subsurface in a less expensive and faster manner.

Cyclic Pore Pressure Generation, Dissipation and Densification in Granular Mixes

Knowledge of cyclic load induced pore pressure generation, post-liquefaction dissipation and volumetric densification characteristics of sands, silty sands, and silts are important for the analysis of performance of loose saturated granular deposits in seismic areas. This article presents results from an experimental study of these characteristics for such soils containing 0 to 100% non-plastic silt. Pore pressure generation characteristics are studied using undrained cyclic triaxial tests. Pre- and post-liquefaction compressibility and coefficient of consolidation, and post-liquefaction volumetric densification characteristics are determined from consolidation data prior to cyclic tests and pore pressure dissipation tests following undrained cyclic tests. Effects of fines content on these characteristics compared to those of clean sands are examined in the context of intergranular void ratio and intergranular contact density concepts.

Predicting the engineering and transport properties of soils using fractal equivalent circuit model: Laboratory experiments

Frequency-dependent electrical measurements of soils contain useful information about their texture and structure that can be linked to their engineering and transport properties. We performed frequency-dependent electrical measurements on 29 natural soils with wide variability in physical and textural properties in a laboratory environment at a constant stress level and in the frequency range of 0.01 Hz–10 kHz. The engineering and hydraulic properties of these soils, that is, the hydraulic conductivity [Formula: see text], void ratio [Formula: see text], fines content [Formula: see text], intergranular void ratio [Formula: see text] and the dry density [Formula: see text] are concurrently measured. The electrical behaviors of the soils are modeled with an equivalent circuit model, which are described by six circuit parameters. Relationships between the circuit parameters and the soil properties (geotechnical engineering and hydraulic) are investigated. Crossplots of frequency exponent [Formula: see text] and resistivity [Formula: see text] and that of [Formula: see text] and grain percent resistivity [Formula: see text] clusters soils with high and low values of hydraulic conductivity, whereas crossplots of relaxation time [Formula: see text] and [Formula: see text] clusters soils with high and low intergranular void ratio. Regression models are developed using the parameters [Formula: see text] and [Formula: see text] to predict the hydraulic conductivity with [Formula: see text]; [Formula: see text] and [Formula: see text] to predict the intergranular void ratio with [Formula: see text] and [Formula: see text] and [Formula: see text] to predict the dry density with [Formula: see text].