Gerald A. Leonards

Bio: Gerald A. Leonards is an academic researcher from Purdue University. The author has contributed to research in topics: Settlement (structural) & Closure (topology). The author has an hindex of 10, co-authored 22 publications receiving 581 citations.

Pulverized coal ash as structural fill

Abstract: Untreated pulverized coal ash, consisting of fly ash with varying percentages of bottom ash, was used as a structural fill material to support the foundation of a new precipitator for a power generating station in Indianapolis, Indiana Geotechnical studies for this fill included evaluation of index and chemical properties, strength, compressibility, compaction and aging characteristics Field density and plate load tests were conducted during fill construction Standard and static cone penetration tests were used to evaluate the consistency of the compacted fill and total settlements of the foundation were measured For this project, compacted coal ash was used successfully as a structural fill material Although the ash was inherently variable, it could be compacted satisfactorily if the moisture content was maintained below the optimum value and if the percentage of fines was below about 60% The load-settlement relation for the foundation on compacted ash could not be inferred from standard or static cone penetration tests, largely because these tests do not adequately sense the effects of prestressing due to compaction Plate load tests proved to be a reliable indicator of the observed settlements (Author)

Compressibility of Clay

Abstract: Experiments on artificially sedimented clays at loading rates as low as 10 -4 offer direct evidence that the compressibility of sedimented clays is much smaller during deposition than that measured in the usual oedometer test. Normally consolidated clays subjected to long periods of secondary compression will not compress along the virgin curve until a substantial pressure increment (as large as 0.4 of the effective overburden pressure) has been added. High quality sampling techniques should include minimizing the time duration between stress release in sampling and stress reapplication in the oedometer. Tests on freeze-dried kaolin clay indicate no measurable viscous retardation to compression over a wide range of load-increment ratios. Subsequent creep strains were approximately linear with log time. A marked reduction in compressibility was observed with decreasing load-increment ratio, but creep strains were found to decrease moderately with increasing effective stress. A hypothesis for the mechanism of compression is proposed and its validity is examined in the light of available data.

Dynamic Compaction of Granular Soils

Abstract: Dynamic compaction was used to improve foundation conditions beneath a large warehouse in Indianapolis, Ind. Approximately 15 ft of fine to medium sand above the water table was densified significantly by dropping a 6.5 ton weight from a height of 40 ft. SPT and cone penetration tests were made before and after compaction to determine the level of improvement. Field measurements were also made using a seismograph to establish the level of vibration produced by each tamp at various distances away from the impact. It was concluded that the depth of significant influence using falling weights as a technique of dynamic compaction is about half that previously considered attainable. The level of compaction achieved was found to be related to the product of the energy per drop times the total energy per unit area: which corresponds to an N value of approx 30 to 35.

Investigation of Failures

Abstract: The problems associated with determining what actually happended after an unexpected instability has occurred are illustrated by case records. Examples are taken from failures of cut slopes in, and embankments on, soft clays and from the failure of a large pile foundation during proof loading. It is then shown how more information can be gleaned from post-failure investigations than has generally been the case up to now, and the important lessons learned are highlighted. It is proposed that a National Center for Investigating Civil Engineering Failures can be created to build up concentrated expertise and to develop rewarding methodologies for investigation of failures, to make the lessons learned cumulative and accessible to the profession, and to provide focal points for rewarding research to reduce significantly the frequency of unexpected failures.

Flexibility of Clay and Cracking of Earth Dams

Abstract: An approximate theory is formulated to calculate the critical tensile strains in an earth dam that result from differential settlements along the axis of the dam. Laboratory apparatus and procedures are developed to estimate the limiting tensile strain at which compacted clay will crack. Comparisons between predicted and observed behavior of five dams indicate that the theory and laboratory tests can be used to predict cracking potential with an accuracy that is satisfactory for practical purposes. The ratio of tensile strain at cracking to compressive strain at failure is a small fraction (approximately 0.01 to 0.1) that shows no evidence of any consistent pattern. Accordingly, it is hazardous to assess the flexibility of compacted earth dams on the basis of stress-strain relations obtained from compression tests. The effects of molding water content and compactive effort on the flexibility of clay was investigated. No consistent relationship between flexibility and plasticity characteristics of the clay was found.

The general and congruent effects of structure in natural soils and weak rocks

Abstract: The engineering properties of naturally occurring sedimentary and residual deposits which are usually treated in geotechnical engineering as ‘soils’ are reviewed, and it is shown that usually they have characteristics due to bonded structure which are similar to those of porous weak rock. While this structure can arise from many causes, its effects follow a simple general pattern that involves stiff behaviour followed by yield. This yield can be described in a similar way to that occurring due to overconsolidation, although it is a separate phenomenon. The effects of structure are as important in determining engineering behaviour as are the effects of initial porosity and stress-history, which are the basic concepts of soil mechanics. As it can be described in a general way, it is concluded that structure and its effects should be treated as a further basic concept of equal importance. L'article passe en revue les proprietes des depots sedimentaires et residuels naturels qui sont nor-malement traites comm...

Simplified Procedure for Estimating Earthquake-Induced Deviatoric Slope Displacements

Abstract: A simplified semiempirical predictive relationship for estimating permanent displacements due to earthquake-induced deviatoric deformations is presented. It utilizes a nonlinear fully coupled stick-slip sliding block model to capture the dynamic performance of an earth dam, natural slope, compacted earth fill, or municipal solid-waste landfill. The primary source of uncertainty in assessing the likely performance of an earth/waste system during an earthquake is the input ground motion. Hence, a comprehensive database containing 688 recorded ground motions is used to compute seismic displacements. A seismic displacement model is developed that captures the primary influence of the system’s yield coefficient ( ky ) , its initial fundamental period ( Ts ) , and the ground motion’s spectral acceleration at a degraded period equal to 1.5 Ts . The model separates the probability of “zero” displacement (i.e., ⩽1 cm ) occurring from the distribution of “nonzero” displacement, so that very low values of calculated...

Simplified Frequency Content Estimates of Earthquake Ground Motions

Abstract: It is often useful in earthquake engineering practice to characterize the frequency content of an earthquake ground motion with a single parameter. Three simplified frequency content parameters are examined: mean period (T m ), predominant period (T p ), and the smoothed spectral predominant period (T o ). These frequency content parameters are calculated for 306 strong motion recordings from 20 earthquakes in active plate-margin regions. These data are used to develop a model that describes the magnitude, distance, and site dependence of these frequency content parameters. Nonlinear regression analyses are performed to evaluate model coefficients and standard error terms. The results indicate that the traditional T p parameter has the largest uncertainty in its prediction, and that previous relationships proposed to predict T p are inconsistent with the current data set. Moreover, T m is judged to be the best simplified frequency content characterization parameter, and it can be reliably estimated.

The Mechanical Aging of Soils

Abstract: Soils age Their engineering properties often improve significantly during aging times of practical interest to engineers This paper provides examples from research and practice It includes a review of the triaxial IDS test, followed by examples of its use to investigage the question of whether the aging improvements result from frictional or cohesive effects Contrary to most current thinking, the soil stiffening and strengthening appears entirely frictional in effect The aging effects described appear mechanical, resulting from dispersive particle movements and internal stress arching under drained conditions The paper concludes with suggestions for using these mechanical aging effects in practice

Elastic properties of marine sediments

Abstract: This report includes discussions of elastic and viscoelastic models for water-saturated porous media, and measurements and computations of elastic constants including compressibility, incompressibility (bulk modulus), rigidity (shear modulus), Lame's constant, Poisson's ratio, density, and compressional- and shear-wave velocity. The sediments involved are from three major physiographic provinces in the North Pacific and adjacent areas: continental terrace (shelf and slope), abyssal plain (turbidite), and abyssal hill (pelagic). It is concluded that for small stresses (such as from a sound wave), water-saturated sediments respond elastically, and that the elastic equations of the Hookean model can be used to compute unmeasured elastic constants. However, to account for wave attenuation, the favored model is ‘nearly elastic,’ or linear viscoelastic. In this model the rigidity modulus μ and Lame's constant λ in the equations of elasticity, are replaced by complex Lame constants (μ + iμ′) and (λ + iλ′), which are independent of frequency; μ and λ represent elastic response (as in the Hookean model), and iμ′ and iλ′ represent damping of wave energy. This model implies that wave velocities and the specific dissipation function 1/Q are independent of frequency, and attenuation in decibels per unit length varies linearly with frequency in the range from a few hertz to the megahertz range. The components of the water-mineral system bulk modulus are porosity, the bulk modulus of pore water, an aggregate bulk modulus of mineral grains, and a bulk modulus of the structure, or frame, formed by the mineral grains. Good values of these components are available in the literature, except for the frame bulk modulus. A relationship between porosity and dynamic frame bulk modulus was established that allowed computation of a system bulk modulus that was used with measured values of density and compressional-wave velocity to compute other elastic constants. Some average laboratory values for common sediment types are given. The underlying methods of computation should apply to any water-saturated sediment. If this is so, values given in this paper predict elastic constants for the major sediment types.