Volume 12, Issue 1-2 (Jan-Dec 2002)

Abstracts

• Ioannis Meladiotis, Konstadinos Moutsopoulos (Laboratory of Engineering Geology, Department of Civil Engineering, Aristotle University of Thessaloniki, GR-540 06 Thessaloniki, Greece): "Hydrogeological conditions and hydraulic behaviour of the fractured aquifer of Mavropigi (Prefecture of Kozani, Greece)." Mining & Metallurgical Annals, vol. 12, issue 1/2, Jan-Dec 2002, pp. 27-38.

A hydrogeological investigation was conducted in the bassin of Ptolemaida-Sarigiol in order to find new water resources. A confined fractured aquifer in the region of Mavropigi was detected. The field and laboratory data indicate that the Mavropigi aquifer can be classified as a double porosity formation. The hydraulic behaviour of the aquifer can be described by a system of partial differential equations, which was solved numerically by the finite volume method. The comparison between the numerical results and the field measurements of the piezometric head was satisfactory. (Article in Greek.) © Mining & Metallurgical Annals, Hellenic Society of Mining & Metallurgical Engineers, 2002.

• Kostas Voudouris (Laboratory of Hydrogeology, Dept. of Geology, University of Patras, GR-261 10 Rio Patras, Greece), Kostas Voudouris (Laboratory of Mineralogy-Geology, Agricultural University of Athens, Iera Odos 75, GR-118 55 Athens, Greece): "Distribution and fractal analysis of the upper-layer parameters of the vadose zone of the alluvial aquifer in the Loutraki basin (Prefecture of Korinthia, Greece)." Mining & Metallurgical Annals, vol. 12, issue 1/2, Jan-Dec 2002, pp. 39-54.

The need to protect the groundwater is prerequisite for its sustainable development and use. Thus, it is necessary to know the geohydraulic parameters of the vadose zone. These parameters relate directly to the ability of restraining various pollutants, which percolate through the vadose zone to the aquifers. This paper deals with the in-situ determination of parameters of the upper part of the vadose zone of the allouvial aquifer of the Loutraki basin (Korinthia Prefecture, Greece). This vadose zone has a thickness, which ranges from 0 m to 125 m and it is characterised by the predominance of fine grained materials. By means of various methods, the hydraulic conductivity, total porosity and effective porosity in the vadose zone of the alluvial aquifer were measured. Seventy samples were collected from the study area. The porosity varies from 22.7% to 51.7% (mean value 30%) and the effective porosity varies from 0.4% to 18.3% (mean value 8%). Hydraulic conductivity shows a wide range of values. Based on the Beyer method, the mean value of hydraulic conductivity is estimated equal to 5×10^-5 m/s. The fractal dimension of effective porosity ranges from 0.61 to 1.9. Larger fractal dimensions of surface samples are associated with larger values of porosity. The spatial distribution of some parameters determined for the study area is shown in the form of contour maps and diagrams. The distribution of the geohydraulic parameters shows the vulnerable regions of the basin, contributing to the estimation of the pollution potential of the vadose zone and the protection of the alluvial aquifer. (Article in Greek.) © Mining & Metallurgical Annals , Hellenic Society of Mining & Metallurgical Engineers, 2002.

• E. Th. Stamboliadis (Technical University of Crete, Dept. of Mineral Resources Engineering, GR-731 00 Chania, Greece): "Strength of brittle materials and energy distribution in comminution." Mining & Metallurgical Annals, vol. 12, issue 1/2, Jan-Dec 2002, pp. 55-76.

The present work is trying to link the basic principles of the strength of materials to the principles of energy-size relationship during comminution. The main assumption is that the energy required for breaking a particle is consumed by the new surfaces created during the breakage event. This assumption is expressed by the equation (23) repeated bellow:

ES_j – ES_o = å₁^jE _{q j} (23)

where ES_j is the surface energy of the material after the breakage event j, and å₁^jE_qj the total energy consumed up to the event j.

The analysis of the principles of the strength of materials gives the relation (10a) repeated bellow:

e_q = b g / (Lr) (10a)

where e_q is the specific energy for breakage, g the surface tension, b the ratio of new surface formed to the surface of breaking force action, L the size of the specimen and r the density of the material.

In the case where g is constant then the total energy required to reduce the particle size from x_o to x_j is given by Rittinger's law while the specific energy can follow either the same law or remain constant, following Kick's law, depending on the variation of b.

In the case where g varies in proportion to the size of the material and b is assumed to remain constant then, according to (10a) the specific energy remains constant. In this case the surface energy before and after any breakage event remains constant, indicating that no energy is required to create the new surface while the energy consumed has a value different than zero. This is thermodynamically impossible. However, this assumption is used when expressing Kick's law by the equation (29b)

å₁^jE _qj = C_k(log x_o – logx_j) (29b)

where C_k is a constant.

Obviously, this expression is a misunderstanding of Kick who simply assumed that the specific energy remains constant during breakage. Equation (29b) is a product of descending workers.

Finally, in the case where the surface tension g varies in proportion to the square root of the size, then the total energy consumed for breaking a material is given by Bond's law, while the specific energy can either follow the same law or remain constant following Kick's law.

Obviously Kick's law is not a marginal case of the laws of Rittinger and Bond, but it is an independent assumption, which can be valid in any case. Recent work [ref. 16] has shown that, depending on size, the specific energy can vary which means that for certain sizes Kick's law does not apply, but this is completely different from saying that Kick's Law is expressed by equation (29b), which does not apply anywhere. (Article in Greek.) © Mining & Metallurgical Annals, Hellenic Society of Mining & Metallurgical Engineers, 2002.

• Sotirios Vardakos (Virginia Polytechnic Institute, USA), Spelios Asproudas (Plastira 82, GR-171 21 N. Smyrni, Athens, Greece), Alexandros I. Sofianos (National Technical University of Athens, School of Mining and Metallurgical Engineering, GR-157 80 Zografos, Athens, Greece), "Numerical simulation of two deep excavations in Athens, Greece." Mining & Metallurgical Annals, vol. 12, issue 1/2, Jan-Dec 2002, pp. 77-104.

The construction of two deep excavations in Athens, supported laterally with piles, is presented. Furthermore, the response of the piles and of the foundation ground of neighbouring buildings is evaluated numerically. To this purpose, sophisticated soil models that differentiate between loading and unloading and allow for strain hardening are employed. Finally, the soil pressures acting on the piles, as evaluated using the numerical procedure, are compared to those suggested by the previous empirical one. (Article in Greek.) © Mining & Metallurgical Annals, Hellenic Society of Mining & Metallurgical Engineers, 2002.

• Ioannis Meladiotis (Université Aristote de Thessaloniki, Département de génie civil, Laboratoire de Géologie du génie civil, GR-541 24 Thessaloniki, Grèce): «R echerche de localisation d’aquifère conglomératique de Pontokomi–Mavrodendri au Bassin de Sarigiol (Macédoine, Grèce)». Mining & Metallurgical Annals, vol. 12, issue 1/2, Jan-Dec 2002, pp. 105-122.

Le Bassin de lignite de Sarigiol qui se situe en Macédoine Centrale au Nord de la ville de Kozani à une distance de 6 km à peu près, correspond à un fosse d’effondrement tectonique créé au Miocène supérieur. Sa superficie qui est limitée à l’Est par la chaîne de montagnes de Vermio (2.052 m), à l’Ouest par la chaîne d’Askio (2.111 m), au Nord par les collines tertiaires du graben de Komanos (771 m) et au Sud par la chaîne de Skopos (1.256 m), couvre une surface de 182 km² , dont l’altitude moyenne est de l’ordre de 650 m. La mine de lignite qui s’y trouve est l’une des plus importantes de Grèce, dont l’extraction occupe 40 km² à ce jour.

La couverture mésozoïque du Trias, Jurassique Crétacé qui affleure largement à la pé-riphérie du bassin, comprend entre autres, des couches de différents types de calcaires, alors que les sédiments détritiques des argiles, des sables des grès, des conglomérats, des marnes et des lignites du Néogène et du Quaternaire remplissent le Bassin de Sarigiol. Le gisement de lignite d’âge Pliocène, se trouve à environ 150 m de profondeur par la surface du sol.

Les roches mésozoïques qui apparaissent à la périphérie du bassin, sont marquées par plu-sieurs accidents tectoniques qui se manifestent sous forme de failles d’échelle kilométrique, de direction NW-SE, NE-SW et E-W.

Deux systèmes de nappe souterraines se développent à la région. La nappe karstique pro-fonde qui se localise dans les calcaires mésozoïques et la nappe exploitable qui se développe aux sédiments du bassin, dont la surface piézométrique se trouve environ 280 m plus haute par rapport à celle de la nappe karstique (niveau piézométrique de nappe karstique : +310 m, niveau piézométrique de nappe exploitable : +588 m).
Au point de prise d΄eau, les aquifères détritiques du bassin, sont les seules ressources d’eau qu΄on peut exploiter pour alimenter en eau potable la ville de Kozani mais aussi pour les besoins agricoles de la région.

L’interruption de fonctionnement d’une douzaine des forages d’exploitation d’eau de la ville de Kozani à cause de l’extractif efficace de la mine et d’autre par le rabattement continu du niveau piézométrique de la nappe exploitable, à mené à la realisation de re-cherches, dont le but essentiel était la localisation de nouvelles ressources d’eau sur la marge ouest du bassin entre les communes de Pontokomi et Mavrodendri.

D’après les recherches géologiques, tectoniques, hydrochimiques, isotopiques, géophy-siques et perforatrices réalisées dans la région ci-dessus, on a déterminé sur la bordure ouest du Bassin de Sarigiol entre les communes de Pontokomi et Mavrodendri une formation conglomératique du Miocène dans laquelle se localise une nappe captive. Ce nouvel aquifère dont la surface piézométrique se trouve dans environ 130 m de profondeur (+590 m), s’alimente par une nappe karstique suspendue d’Askio. (Article in Greek.) © Mining & Metallurgical Annals, Hellenic Society of Mining & Metallurgical Engineers, 2002.

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