Soil Reinforcement by Rigid Inclusions: Contamination of an Oil Storage Tank

An oil storage tank at the North suburb La Goulette (Tunisia) was founded on reinforced soft soil by floating sand columns of 6 m in length and 11% of improvement area ratio within a thick compressible clayey soil. Serious contamination of tank due to very significant differential settlement forces the decision to terminate its operations. Reinforcement by inclined rigid inclusions was suggested to neutralize the evolution of consolidation settlement in sub compressible clay layers. Numerical predictions were implemented for the study of the post behavior of tank on reinforced soil by rigid inclusions. Effectiveness of solution using inclined rigid inclusions is illustrated and, then, discussed. Modeling of the contact between the rigid inclusions, by means of element of interfaces, and soft clay has been seen of great importance when predicting the evolution of long term settlement

Educating Students Through Understanding the Pathology of Geotechnical Projects

Three projects of end of studies which are related to soil mechanics pathology case histories were undertaken by students at civil engineering department of National Engineering School of Tunis. The two first projects dealt with Joumine and Sidi Saâd earth dams cases. For Joumine dam, concrete slabs of the spillway have been affected by serious disorders. The first disorder is related to the swelling nature of soil foundation of concrete slabs. The second disorder is attributed to high excess pore pressure responsible of slabs up risings. As solution the jet grouting technique was designed to eliminate high pore pressure in the soil foundation of slabs. For Sidi Saâd dam disorders were attributed to high active soil pressures exerted on retaining walls of the spillway. As solution anchored cables were adopted to improve the stability of concrete walls. The third project dealt with four engineering structures crossing Tunis La Goulette express route. All approach slabs were affected by differential settlements due to the existence of highly compressible thick soft clay layers. As solution three soil improvement techniques (rigid inclusions, stone columns prefabricated vertical drains) were compared to stop non admissible consolidation settlements. For each case history, the methodology to diagnose causes of disorders is first presented, second, the utilized approaches, especially those involving finite element codes usage, are highlighted, finally proposal of remedies to re establish suitable exploitation of projects are exposed. This paper well illustrates the great importance for under graduated students, when preparing their works of end of projects, to more understand fundamentals in soil mechanics in parallel with treating serious problems of pathology of case histories

Comparison Between Stone Columns and Vertical Geodrains with Preloading Embankment Techniques

In the framework of “Radès-La Goulette“bridge project (Tunisia), this study focuses on the construction of embankments located in north Lake of Tunis. These embankments with averaged height of about 6 m are founded on highly compressible clayey sand and muddy sand layers. A soil improvement technique is then imposed, to overcome the lack of low bearing capacity and high pronounced settlements. Two solutions of soil improvement have been studied; the first one consists in vertical “Geodrains” drilled until 10 m depth associated with step by step construction of preloading embankment. The second technique is stone columns reinforcement up to 10 m depth. It is focused at estimation of bearing capacity and prediction of settlement of reinforced soil by handling the recent elaborated software programme “Columns”. The evolution of consolidation settlement of embankments as a function of time is also considered. The consolidation of improved soil is studied by using the “poroelastic” prediction model and the Barron’s theory. A comparison between the two soil improvement techniques from the technical and economical viewpoints is presented. Compared to the “Geodrains” technique, the reinforcement by stone columns including the execution of embankments approximately leads to a gain of eight months and slightly cost reduced

Contribution à l'étude des sédiments marins tunisiens (cas des ports de Radès et de Gabès)

Le secteur du transport maritime assure le plus grand volume des échanges commerciaux entre la Tunisie et des pays du monde entier. L entretien régulier des ports, particulièrement par le dragage des sédiments qui s y accumulent, est indispensable pour garantir une circulation maritime fluide et sécuritaire. En Tunisie, les sédiments dragués sont soit rejetés en mer soit mis en dépôts terrestres. Bien que le rejet en mer soit interdit dans certains cas, par les critères environnementales adoptés, il constitue la solution la plus économique et donc la plus fréquemment utilisée. Dans le cadre de cette étude les sédiments de deux ports : le port de Radès et le port de Gabès ont été caractérisés en vue de comprendre leurs comportements et proposer au moins à un des deux cas une nouvelle alternative de gestion à savoir une valorisation dans un matériau de construction ou routier. Une telle solution doit présenter un grand intérêt économique et environnemental. Les sédiments du port de Radès sont étudiés car ils représentent le plus grand volume des sédiments dragués en Tunisie et que ce port est le plus important dans l activité du transport marin. Les sédiments du port de Gabès sont considérés dans cette étude car ils posent un grand problème écologique à cause des rejets industriels. La caractérisation a concerné la détermination et l analyse des propriétés physiques, minéralogiques, chimiques et environnementales des sédiments. Cette étude a permis de dresser des fiches synoptiques assez complètes des propriétés des sédiments du port de Radès et du port de GabèsCommercial harbors, which represent the basis for numerous exchanges of goods and services at the national and international levels, play a key role in the Tunisian economy. Then, dredging of accumulated sediments has always been required to have a proper functioning of trade by sea. These sediments are either discarded at sea or landfilled. Disposal at sea is prohibited for polluted sediments but it remains the most adopted solution in Tunisia as it is the cheapest one.The objective of this research project is to study the environmental and geotechnical characteristics of sediments dredged from two Tunisian harbors: Rades and Gabes and to find new paths of management of at least one of these dredged sediments. Focus is made on the possibility of a recycling method, which consists in the reuse of sediments as added product in construction or road materials. This solution should have a great economic and environmental interest. The first harbor represents the main facility place in the national transport chain. The second one is selected as its sediments present a serious ecological constraint caused by the discharge of wastes into the marine environment. Physical, chemical, mineralogical and environmental characteristics are determined in order to draw up an accomplished synopsis of studied sedimentsVILLENEUVE D'ASCQ-ECLI (590092307) / SudocSudocFranceF

Numerical Simulation of the Effect of Loading Angle on Initial Cracks Position Point: Application to the Brazilian Test

The Brazilian Test is the most used test to determine the indirect tensile strength for brittle materials like concrete. It has been observed that the success of the test depends on the cracks initiation point position and therefore the arch loading angle; a crack appears in the center of the disk when the test is valid. To this effect, using Fast Lagrangian of Continua code FLAC2D; numerical analyses were performed to study the impact of the arch loading angle on the initial crack’s position in a 70 mm diameter Brazilian disk of concrete and mortar under loading arch 2α which varies from 5–45°. The distribution of stresses and the tensile strength at the center of the Brazilian disk obtained numerically was closely similar to analytical and experimental existing solutions. The results showed that to obtain a meaningful and validated test with the most accurate indirect tensile strength, it is recommended to take a loading arch 2α ≥ 20° for the concrete and 2α ≥ 10° for the mortar

Modèle micromécanique (corrélation des propriétés hydrauliques et acoustiques des matériaux cimentaires)

L objectif de cette thèse est la caractérisation de la porosité de la pâte de ciment partiellement saturée par des ondes ultrasonores. Les corrélations entre les vitesses ultrasonores et la porosité ont été étudiées en se basant à la fois sur les résultats expérimentaux et la modélisation micromécanique. Des mesures expérimentales de vitesses ultrasonores longitudinales et transversales en fonction du rapport eau/ciment et à différents états de saturation ont été réalisées sur la pâte de ciment avec et sans entraîneur d air. En modélisation micromécanique, les effets de saturation ont été modélisés en supposant que la structure poreuse est formée d inclusions ellipsoïdales de facteur de forme variable selon le rapport E/C. A n d estimer les modules homogénéisés élastique de la pâte de ciment et de pâte de ciment à entraîneur d air différents modèles micromécaniques ont été étudiés. Les résultats de la modélisation micromécanique ainsi que les résultats expérimentaux ont montré que les vitesses des ondes longitudinales et transversales de la pâte de ciment à l état sec sont inférieures à ceux de l état saturé. Cet effet est tout aussi important pour l ensemble des rapports E/C. Le modèle de Mori-Tanaka a donné la meilleure estimation des résultats expérimentaux mesurés sur la pâte de ciment. Alors que le modèle auto-cohérent a donné la meilleure estimation des propriétés mécaniques et ultrasonores de la pâte de ciment avec entraîneur d air.Les résultats de ce travail devraient constituer le fondement d un processus d inversion et d amélioration de la détermination de la porosité de la pâte de ciment par les ultrasons en tant que méthodes non destructivesThe objective of this work is the characterization of unsaturated cement paste porosity through the use of ultrasonics. The correlation between ultrasonic velocity and porosity in cement paste material is studied based on both micromechanical modelling and experiments.Experimental measurements of ultrasonic longitudinal and transverse velocities as a function of water to cement ratio and under different saturation states were performed on cement paste with and without air-entrained adjuvant. In the micromechanical modeling, the effects of saturation were modeled by approximating the porous structure as a penny shaped ellipsoidal inclusions of aspect ratio varying with the W/C ratio. Several different micromechanical models for estimating the homogenized elastic moduli of cement paste and air-entrained cement paste were studied.The micromecanical modelling has shown that the longitudinal and transverse wave velocities of the dry cement paste are lower than those of the water saturated cement paste. This effect is equally prominent for all the cement paste W/C ratios. The model of Mori-Tanaka was found to give the best t with the experimental results for the cement paste modeling. While, the self-consistent model gave the best estimate of the mechanical and ultrasonic air-entrained cement paste properties when compared to the laboratory experimental results.The ndings of this work should be most appropriate as a foundation for an inversion process and improved cementitious material porosity determination by nondestructive methodsVILLENEUVE D'ASCQ-ECLI (590092307) / SudocSudocFranceF

Stability analysis of an embankment lying over a column reinforced soil

International audienceThe design against failure of an embankment resting upon a soft soil improved by a group of columns is investigated with the help of the yield design homogenization approach. Assuming that both constituents of the reinforced ground are purely cohesive materials ("lime column" technique), an upper bound estimate for the macroscopic strength condition of the reinforced soil as a homogenized medium is first obtained, providing definite evidence of a shear strength anisotropy associated with the reinforcement preferential orientation. The kinematic method of yield design is then performed on the basis of such a criterion, making use of rotational failure mechanisms involving slip circles in the reinforced ground. Upper bound estimates are finally obtained for the embankment stability factor, as functions of the degree of reinforcement and relative thickness of the soil layer. These results are compared with those derived from a simplified analysis, where the reinforced soil is assumed to exhibit an averaged isotropic cohesion. This comparison clearly indicates that the latter simplified analysis may produce quite unsafe estimates for the embankment stability, which can be attributed to the fact that it fails to capture the inherent strength anisotropy of the reinforced soi

Tunis soft soil sensitivity

The marine environment deposits of Tunis soft soil during the quaternary age and the abundance of non swelling minerals (quartz) resulted in a low electro-kinetic potential and a flocculated structure. The Tunis soft soil leached out afterwards under “hard” ground water (cations Ca2+) conditions, leading finally to pore water quality with a high concentration of polyvalent ions and therefore with limited possibilities to developing highly sensitive clay. At locations where Tunis soft soil remained in contact with active organic matter, increasing the negative charges at the particle surface, the double layers around the particles were expanding. The electro-kinetic potential became higher, implementing larger repulsive forces between particles. At any type of remoulding of such type of soft soil, these forces will prevent flocculation of the clay particles. This reduces remarkably the remoulded shear strength and therefore largely increases the sensitivity of the clay leading to high sensitivity of many of the Tunis soft soils. The levels and the origin of such sensitivity in Tunis soft soils are going to be pointed out