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Geochemical characterisation of the outcropping rock masses of the immediate vicinity of wadi el-kaffrein dam site (Jordan)

  • Abu-Zeid N. 
  • Vuillermin F. 
Article

Abstract

this paper, the geomechanical characteristics of the discontinuities present in the rock masses, exposed in and around the existing Kaffrein dam site (Western have been investigated for a probable heightening project of the dam in the near future.

this purpose, eighteen detailed line surveys were carried out to determine the geometrical and the mechanical properties of the discontinuities. These were located on both the abutments as well as on the exposed rocks near the reservoir area.

of the discontinuity orientations, plotted on equal-area stereographic contour nets, have indicated the presence of two sub-vertical joint sets and a one attributed to bedding planes. On the one hand, right abutment rock masses are characterised by low persistence, closely spaced joints that caused formation of small to very small block sizes. On the other hand, exposed rocks on the left abutment reflect the presence of closely to widely spaced, persistent joints which result in small sized blocks.

mass Uniaxial Compression Strength (UCS) was determined both in the laboratory and in situ. In situ measurements classified the rock masses as while those measured in the laboratory, classified the rock masses as weak to moderately strong. Low UCS values were assigned to samples taken the left abutment. Such values (UCS<20 Mpa) are believed to be questionable in view of the large difference observed between these values and those from in situ measurements (UCS ⋍ 80 MPa).

mass shear strength behaviour of the studied rocks was estimated considering the JRC, JCS of the main discontinuity sets as well as the empirical of Barton and Choubey (1977). The estimated shear strength envelopes relevant to the rock masses of both abutments were similar, and thus, they similar shear strength characteristics. These results indicate the necessity of conducting further laboratory tests on samples to be taken from the left in order precisely to determine the spatiel variation of the shear strength parameters, taking into consideration that future works, regarding the heightening, are to be done on the left abutment.

mass quality was determined through the employment of the two widely known geomechanical classification systems: RMR and Q. Both systems a fair to good quality class to the rocks of both abutments. The cross correlation of their results gave a regression equation that is closely similar to of Bieniawski. However, it should be stressed that its validity is applicable, preferably, to the study area.

geological and geomechanical investigations, presented in this work, established two main problems that are directly related to the dam ans/or to any developments or works related to it. The first, concerns the heterogeneous nature, from the fracture intensity point of view, of the rock masses of the formation. While the second, concerns the permeable alluvial deposits which cover the reservoir area, through which, an unallowable quantity of water is taking place.

conveyed results are believed to furnish valuable technical information regarding the geomechanical behaviour of the exposed rock masses in the vicinity dam. This information could be used to direct or to lead future field &/or technical works in an efficient way in order to pass to the design and execution.

Keywords

Rock Mass Uniaxial Compression Strength Reservoir Area Rock Quality Designation Limestone Formation 

Caractérisation Géomécanique des masses rocheuses affleurant près du site du barrage d’El-Kaffrein (Jordanie)

Résumé

En vue de la surélévation probable du barrage de Kaffrein (Ouest de la Jordanie) les caractéristiques géomécaniques des discontinuités des masses rocheuses été étudiées. Dans ce but, dix-huit stations de mesures ont été implantées sur les Culées et sur les Culées et sur les affleurements rocheux près du réservoir.

L’analyse des discontinuités a révélé la présence de deux ensembles de joints sub-verticaux et d’un troisième correspondant aux plans de stratification. Le rocheux de la culée de droite se caractérise par des joints peu continus et rapprochés, délimitant des blocs de petite ou très pettite taille. Les roches de a culée de gauche présentent des joints soit rapprochés soit éloignés et modérément continus, ce qui délimite des blocs de petite taille.

La résistance en compression simple a été mesurée à la fois en laboratoire et in situ. Les mesures in situ conduisent à qualifier les masses rocheuses de résistantes alors que celles effectuées en laboratoire les qualifient de faiblement à modérément résistantes. Les valeurs faibles correspondent à des échantillons de la butée de gauche. Ces valeurs (<20 MPa) posent problème, si l’on se réfère à celles obtenues in situ (⋍ 80 MPa), la différence étant très importante.

Le comportement des massifs rocheux en résistance au cisaillement a été estimé en prenant en compte la résistance et la rugosité des principaux ensembles de discontinuité, ainsi que les formules de Barton et Choubey (1977). Les estimations obtenues donnent des valeurs de résistance au cisaillement similaires pour les deux culées; il faudra donc réaliser de nouveaux essais en laboratoire sur des échantillons de la culée de gauche pour préciser les variations précises dans l’espace de la résistance au cisaillement, car les futurs travaux concernant la surélévation de l’évacuateur de crue seront réalisés dans cette culée.

La qualité du massif rocheux a été déterminée et utilise les deux systèmes de classification bien connus, les systèmes de Bieniawski et de Barton. Les deux les roches des deux culées comme étant de moyenne à bonne qualité.

Les études géologiques et géomécaniques présentées dans cette étude ont attiré l’attention sur deux problèmes principaux qui concernent directement le barrage et/ou tous travaux futurs en liaison avec ce dernier.

Le premier concerne l’hétérogénéité des massifs rocheux de la formation de Hummar du point de vue de l’intensité de la fracturation. Le second concerne dépôts alluviaux perméables qui recouvrent la zone du réservoir et au travers desquelles se produisent des fuites d’eau en quantités beaucoup trop élevées.

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Copyright information

© International Assocaition of Engineering eology 1997

Authors and Affiliations

  • Abu-Zeid N. 
  • Vuillermin F. 
    • 1
  1. 1.Department of Geological and Paleontological SciencesUniversity of FerraraFerraraItaly

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