12 research outputs found
Numerical modeling of the face reinforcement of Djebel El-Kantour tunnel face (highway east-west)
No full textThe extension of communication ways (roads, highways, railways) often involves difficult crossings that usually lead to the construction of important structures such as tunnels. Similarly congestion on ground surface in cities necessitates the construction of underground structures (roads and metros). Terrain stability during construction especially in the coalface is one of the major problems related to the construction of these structures. This paper presents numerical modeling of the mechanical behavior of the rock face of the DJebel El-Kantour tunnel (East West Highway) reinforced by fits. In order to minimize on maximum the cost of numerical simulations, the reliability of three methods of homogenization of reinforced soil (improving cohesion, improving the cohesion and angle of friction and ultimately improve the Young\u27s modulus) is tested by comparing the results of numerical simulations to the displacements measured insitu
Calculating the Dynamic Impedances of Foundations and their Effect on the Seismic Response of Structures: Analytical and Numerical Study
No full textThis study evaluates the movement of a frame built on soft soil under seismic excitation taking into account soil-structure interaction. First, the study was evaluated using the finite element method, then, by using a substructure method which modelled the soil using springs and dampers in a linear and nonlinear study. Rheological models were determined using impedance functions, calculated using a numerical program CONAN. These dynamic impedances are shown in the displacement vector of a three-degrees-of-freedom frame, which was calculated on the basis of lateral forces distributed over the structure height using the equivalent static method. In this regard, two different calculation norms were chosen; RPA2003 and UBC97. Finally, a parametric study was carried out, based on the effects of soil densification and the foundation geometry on the response of the RC frame
Modeling the Behavior of Geotechnical Constructions Under Cyclic Loading with a Numerical Approach Based on J. Lemaitre Model
No full textOn the Practical Use of Advanced Constitutive Laws in Finite Element Underground Structures Analysis
No full textThis article emphasizes the value of applying sophisticated constitutive soil models in numerical modeling as daily geotechnical practice. The capabilities of two different constitutive relations for the modeling of the second Heinenoord bored tunnel are compared. The hypoplastic model of Wolffersdorff for granular materials (Hypo) is a relatively simple model without recourse to yield surface or plastic potential based on rational mechanics, whereas the chosen elastoplastic model, the Hardening Soil Model (HSM) belongs to the non-associative plasticity with double hardening. A modification of the hypoplastic model with improved intergranular strain (IGS) was tested, leading to improve model behavior. Comparisons between numerical simulations and experimental values demonstrate the advantages of using the hypoplastic model with improved intergranular strain (IGS)
Numerical Modeling of the Degradation of the Normal Stress Under Large Number of Shearcycles
No full textThe evaluation of friction is an important element in the verification of stability and the determination of the bearing capacity of piles. In the case of cyclic stress, the soil-pile interface has a relaxation which corresponds to a fall in the horizontal stress which represents the normal stress at the lateral surface of the pile. This paper presents an explicit formulation to express the degradation of the normal stress after a large number of shear cycles as a function of cyclic parameters. In this study we are interested in the exploitation of the cyclic shear tests carried out by Pra-ai with imposed normal rigidity (CNS) in order to demonstrate the phenomenon of falling of the normal stress. The approach presented in this paper consists in proposing a simple expression for estimating the degradation of normal stress as a function of cyclic shear parameters after a large number of cycles. The validation of this approach is verified by the application of this formulation to a real case where the comparison of the simulations made by this approach with those recorded on site shows the good adaptation of this approach to this type of problems
Внесок у мікромеханічне моделювання поширення зсувної хвилі в піщаному відкладенні
No full textThe object of study is the vertical wave propagation in a sand deposit. This paper is aimed at analyzing the vertical wave propagation in a sand deposit through micromechanical modeling that inherently takes account of intergranular slips during deformation. Such a problem, which is part of the general framework of wave propagation in the soil, has long been analyzed using continuum models based on approximate behavior laws. For this purpose, a 2D Discrete Element Method (DEM) model is developed. The DEM model is based on molecular dynamics with the use of circular shaped elements. The intergranular normal forces at contacts are calculated through a linear viscoelastic law while the tangential forces are calculated through a perfectly plastic viscoelastic model. A model of rolling friction is incorporated in order to account for the damping of the grains rolling motion. Different boundary conditions of the profile have been implemented; a bedrock at the base, a free surface at the top and periodic boundaries in the horizontal direction. The sand deposit is subjected to a harmonic excitation at the base. Using this model, the fundamental and resonance frequencies of the deposit are first determined. The former is determined from the low-amplitude free vibration and the latter by performing a variable-frequency excitation test. It is noted that there is a significant gap between the two frequencies, this gap could be attributed to the degradation of the soil shear modulus in the vicinity of the resonance. Such degradation is well proven in classical soil dynamics. The effects of deposit height and confinement on resonance frequency and free-surface dynamic amplification factor are then investigated. The obtained results highlighted that the resonance frequency is inversely proportional to the deposit’s thickness whereas the dynamic amplification factor Rd increases with the deposit’s thickness. In the other hand, when the confinement increases the deposit becomes stiffer, which results in reducing the amplification. Such result is in accordance with theoretical knowledge which states that the most rigid profiles such as rocks do not amplify seismic movement.Об’єктом дослідження є поширення вертикальних хвиль у піщаному покладі. Ця стаття направлена на аналіз поширення вертикальних хвиль у піщаному покладі за допомогою мікромеханічного моделювання, яке враховує міжзернове ковзання під час деформації. Така задача, яка є частиною загальної теорії поширення хвиль у ґрунті, вже давно аналізується з використанням континуальних моделей, що базуються на наближених законах поведінки. Для цього розроблено 2D модель методу дискретних елементів (МДЕ). Модель МДЕ базується на молекулярній динаміці з використанням елементів круглої форми. Міжзеренні нормальні сили на контактах розраховуються за лінійним законом в'язкопружності, а дотичні сили – за ідеально пластичною в'язкопружною моделлю. Для врахування демпфування руху кочення зерен використовується модель тертя кочення. Реалізовано різні граничні умови профілю: корінна порода в основі, вільна поверхня вгорі та періодичні границі в горизонтальному напрямку. Піщаний поклад піддається гармонічному збудженню біля основи. Використовуючи цю модель, спочатку визначають основну та резонансну частоти покладу. Першу визначено з низькоамплітудних вільних коливань, а другу – шляхом проведення тесту зі змінною частотою збудження. Відзначено, що між цими двома частотами існує значний розрив, який можна пояснити деградацією модуля зсуву ґрунту поблизу резонансу. Така деградація добре доведена в класичній динаміці ґрунтів. Далі досліджено вплив висоти покладу та його залягання на резонансну частоту та коефіцієнт динамічного підсилення вільної поверхні. Отримані результати показали, що резонансна частота обернено пропорційна товщині покладу, тоді як коефіцієнт динамічного підсилення Rd зростає зі збільшенням товщини покладу. З іншого боку, зі збільшенням концентрації осад стає жорсткішим, що призводить до зменшення коефіцієнта підсилення. Такий результат узгоджується з теоретичними уявленнями про те, що найжорсткіші профілі, такі як гірські породи, не підсилюють сейсмічні рухи
Explicit Modeling of the Cyclic Behavior under a Large Number of Cycles: Application to the Case of Sand
No full textThe estimation of deformations after a large number of cycles is a major concern of geotechnical engineers. This paper presents an explicit formulation of the accumulated cyclic volumetric strain. This study is concerned with cyclic triaxial tests simulated through the calculation by the Finite Element Method. The parameters of identification of the first cycle (loading-unloading) are determined step by step, using, as a soil behavior model, the Soft Soil Hardening Model, then, the behavior of the soil after N cycles (N ---gt--- 1000) is simulated through the formulation proposed as a pseudo-creep. The comparison of the proposed method with several cyclic triaxial tests and a shallow foundation under cyclic loading approves the good compatibility of the proposed formula for this type of problem. This study does not take into account the effect of the grain size and the void ratio, things that can be translated by the coefficients C1 and C2
Improving geotechnical properties using paper ash and olive pomace
No full textSoil stabilization techniques play a crucial role in improving soil quality, reducing construction costs, and addressing environmental and mechanical challenges encountered in civil engineering. Faced with low-quality soils, several researchers have explored innovative solutions by using natural waste materials. New approaches are being developed to recover local waste and reuse it in civil engineering applications, particularly in earthworks. In this study, the goal is to experimentally compare the impact of two types of waste on the stabilization of clay soils, by testing different percentages (2%, 4%, 6%, 8%) through various laboratory tests, such as compressive strength, shear strength, and oedometer compression test. The results obtained are analyzed to evaluate the effectiveness of these wastes in soil treatment. The preliminary study conducted on the clay soil showed a significant improvement in its mechanical properties, which could enhance its stability and bearing capacity
Modélisation constitutive du comportement cyclique des sables en condition drainée
No full textDans cette étude, une modélisation numérique simple du comportement des sables sous chargement cyclique est proposée ; la démarche proposée consiste, en condition drainée, à déterminer les paramètres caractérisant le chemin cyclique moyen du sol sous l’'effet de N cycles dûment caractérisés, et à traduire l'’effet cyclique par une déformation volumique cumulée ainsi que par une variation de module du sol. Dans cette étude on s’'intéresse à des essais triaxiaux cycliques simulés au moyen d’'un calcul en éléments finis utilisant le programme Plaxis. On détermine les paramètres d’'identification du premier cycle (charge-décharge) réalisé pas à pas en prenant, comme modèle de comportement du sol le modèle HSM. Puis le comportement après N cycles (N>1000) est simulé par la formulation proposée comme un pseudo-fluage. La comparaison de la méthode proposée à plusieurs essais triaxiaux cycliques confirme la bonne adaptation du modèle proposé à ce type de problème
On the behavior of a granular soil deposit subjected to horizontal vibration. A discrete element modeling
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