Fly ash and bottom ash obtained from coal-fired electric power generating stations can be used as alternatives to natural materials for the construction of structural fills. The engineering properties of coal ash pertinent to its use in structural fills are discussed. Four case studies of coal ash structural fills are presented. The performance of these fills was monitored during and after construction. These cases demonstrate that the physical behavior of fly ash is similar to that of silt and that it can be handled with similar methods. Groundwater monitoring data from existing fly ash fills are presented to show the impact that ash leachate migrating into the groundwater regime has on water quality. Results of long-term corrosion studies are presented to show that metals buried in ash, used in such structures as culverts, cable ducts, guard rails and streetlights, are not adversely affected. Ash leachate was found not to be detrimental to good-quality concrete structures. Key words: fly ash, fill, compaction, leachate, corrosion, concrete.
The results are reported of a laboratory testing program to determine the permeability ratio, rK, (ratio of coefficients of permeability for flow parallel to and perpendicular to the soil layers) of samples of New Liskeard varved soil. The maximum value of rK is less than 5, which is perhaps significantly smaller than values usually assumed for varved soils. To explain these results, tests were conducted to determine the permeability characteristics of the constituent soils of the varves. Information is given concerning the test methods, the determination of the influence on permeability of soil disturbance at the cut surfaces, and the finding that this soil behaved according to Darcy's law at small values of hydraulic gradient.
The paper presents a description of several uses of radiographs of soil samples that have been found valuable in a geological and geotechnical investigation of varved soil. The radiographs were taken while the soil was still in the sampling tubes, thus enabling examinations to be made of the samples before they were extruded.The uses to which the radiographs have been primarily made are to record in detail the soil stratigraphy, to make examinations of the soil structure and texture, and to help plan laboratory-test programs.Damage to 'undisturbed' samples, in the form of transverse cracks created during the sampling process, was detected by examination of the radiographs. Such features as these might not be detected in extruded samples because they are obscured by smeared soil on the surface of the sample and because cracks would tend to become closed during extrusion.A brief discussion is included of the requirements for making radiographs.
The leaching behavior of bituminous coal fly ash has been studied by both field and laboratory tests of ash and water specimens taken from a fly ash disposal site. The site, an abandoned sand quarry which was filled with fly ash, covered, and landscaped in 1974, was instrumented with nine piezometers in January 1978. Six multilevel piezometer nests were installed along the major groundwater table gradient in August 1978. Groundwater specimens have been removed and analyzed periodically since the piezometers were installed. Specimens of ash removed during piezometer installation were tested, first to extract the interstitial water from the ash specimens by a pressure displacement technique, and then to obtain leachates from the ash specimens by shake and column leaching procedures. The results of these tests are used in this paper to compare the composition of leachates derived from the different laboratory leaching methods with the analyses of extracted interstitial waters from corresponding ash specimens and with analyses of groundwater from the field sampling program. The suitability of laboratory leaching tests for predicting the field behavior of coal fly ash is discussed in the light of the results obtained in this comprehensive leaching study.
The results are reported of an investigation to determine the it1 sit11 permeability ratio of a large body of varved soil near New Liskeard, Ontario. Permeability ratio is defined as the ratio of coefficients of permeability for flow parallel to and perpendicular to the varves. The method used was to measure with piezometers the pattern of water pressures within a natural slope and to determine by trial and error calculations the value of permeability ratio which would yield a similar pattern of water pressures. The value of this permeability ratio was found to be rK < 5.The it1 situ magnitudes of hydraulic gradient were appreciably smaller than unity and this brought into question the usual assumption that the flow obeyed Darcy's law. Comparisons between calculated patterns of water pressure based on Darcy flow and non-Darcy flow and measured patterns of water pressure indicated that the best fit was obtained based on the assumption of Darcy flow.It is hypothesized that soils consisting of distal varves have small values of permeability ratio and that soils consisting of proximal varves can have large values of permeability ratio.L'article prCsente les rksultats d'une Ctude du rapport de permeabilitt in sit11 dans un massif de sol varvk prbs de New Liskeard, Ontario. Le rapport de perm&abilitC est dtfini comme 6tant le rapport des coefficients de permCabilit6 correspondant i des Ccoulements parallele et perpendiculaire aux varves. La mCthode utiliste a consist6 B mesurer a I'aide de piCzometres la distribution des pressions interstitielles dans une pente naturelle et h determiner par un calcul par approximations successives la valeur du rapport de permCabilitC qui conduisait a une telle distribution. La valeur du rapport de permCabilitC a ainsi kt& etablie a,., < 5 .Les gradients hydrauliquesin sir11 Ctaient nettement inferieurs aI'unitC, ce qui a conduit a mettre en doute I'hypothkse classique d'un Ccoulement obeissant B la loi de Darcy. Cependant la comparaison des reseaux de pressions interstitielles calculCs a partir des hypotheses d'un ecoulement obkissant ou non a la loi de Darcy, avec les reseaux observes a montre que la meilleure concordance etait obtenue pour I'Ccoulement obeissant a la loi de Darcy. I1 est finalement suggere que les sols 1 varves espacCes ont des rapports de permCabilitC faibles et que les sols i varves serrtes ont des rapports de permeabilitt importants.[Traduit par le journal]
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