Hasil Pencarian  ::  Simpan CSV :: Kembali

"This book explains the hypoplastic modelling framework. It is divided into two parts, the first of which is devoted to principles of hypoplasticity. First, the basic features of soils mechanical behaviour are introduced, namely non-linearity and asymptotic properties. These features are then incorporated into simple one-dimensional hypoplastic equations for compression and shear. Subsequently, a hypoplastic equivalent of the Modified Cam-Clay model is developed in 2D space using stress and strain invariants to demonstrate key similarities and differences between elasto-plastic and hypoplastic formulations. Lastly, the mathematical structure of hypoplastic models is explained by tracing their historical development, from the early trial-and-error models to more recent approaches. In turn, Part II introduces specific hypoplastic models for soils. First, two reference models for sand and clay are defined. After summarising their mathematical formulations, calibration procedures are described and discussed. Subsequently, more advanced modelling approaches are covered: the intergranular strain concept incorporating the effects of small strain stiffness and cyclic loading, viscohypoplasticity for predicting rate effects, soil structure to represent structured and bonded materials and soil anisotropy. The book concludes with a description of partial saturation and thermal effects: topics that are increasingly important to the disciplines of energy and environmental geotechnics.Selecting a constitutive model and its parameters is often the most important and yet challenging part of any numerical analysis in geotechnical engineering. Hypoplasticity involves a specific class of soil constitutive models, which are described in detail here. The book offers an essential resource, both for model users who need a more advanced model for their geotechnical calculations and are mainly interested in parameter calibration procedures, and for model developers who are seeking a comprehensive understanding of the mathematical structure of hypoplasticity."

"Several studies have already been published in order to better understand the behaviour of interfaces. Different experimental methods, including direct shear tests, simple shear test, and tortional ring test, and also various constitutive models were presented to modelize the behaviour of the interface. These studies revealed that the main factors that affect the behaviour of the interface include the roughness of the interface, the soil mineralogy, the soil density, and the normal stress applied. This work was therefore directed primarily to better understand the overall behaviour of the interface and the influence of these factors in a monotonic and cyclical solicitation. Through the simulation of a direct shear test at constant normal stress (CNL) in FLAC 5.0, several typical behaviours, including degradation of shearing resistance and contractancydilatancy, have been observed and modelled. At first, the law of Mohr-Coulomb and its correspondent failure criterion have been implemented. Then several models have been proposed to model more precisely the behaviour. Finally, two cyclicals laws, the law of Ramberg-Osgood law and Byrne, originally developed for the soil, have been implemented in this model. This study has verified the consistency of the results and has determined whether the injection of such laws is sufficient to modelize the behaviour of the interface under cyclic loading. "

"ABSTRACTThe development and extension of large cities creates a need of multiple shallow tunnels in the soft ground of built areas. Excavating a tunnel generates ground displacements and deformations which can affect existing buildings and services in urban sites and can lead to unacceptable damages. Prediction of the ground settlement caused by the tunnel excavation has been a major engineering challenge. A numerical simulation using finite element method was implemented in the aim of developing a procedure for forecasting the movement induced by tunneling. This study describes the modelling procedure, comparing one procedure in a complete stages of modelling (called phases modelling) taking into account different phases simulating the different kinds of interaction between the tunnel and the soil (deconfinement, lining installation, pore pressure applied on the lining, and weight of the lining) and one in a simple way called `deconfinement modeling', simulating the excavation using a stress decrease vector exerted on the excavation boundary in the opposite to the initial ground stress described by a scalar parameter A. (the deconfinement rate). A shallow lined tunnel is analyzed in a two dimensional analyses, and observations are made for the settlement at the surface and at the tunnel crown, the deformations of the tunnel opening, and the stress path around the tunnel. Comparison is conducted using two soil models : the Mohr-Coulomb model and the CJS model. Observations of the results and comparison with the experimental data demonstrate that the deconfinement modeling is adequate for the analyses of settlement induced by tunneling only if a good modeling of the soil behavior is considered."

"The purpose of this book is to bridge the gap between the traditional Geomechanics and Numerical Geotechnical Modelling with applications in science and practice. Geomechanics is rarely taught within the rigorous context of Continuum Mechanics and Thermodynamics, while when it comes to Numerical Modelling, commercially available finite elements or finite differences software utilize constitutive relationships within the rigorous framework. As a result, young scientists and engineers have to learn the challenging subject of constitutive modelling from a program manual and often end up with using unrealistic models which violate the Laws of Thermodynamics. The book is introductory, by no means does it claim any completeness and state of the art in such a dynamically developing field as numerical and constitutive modelling of soils. The author gives basic understanding of conventional continuum mechanics approaches to constitutive modelling, which can serve as a foundation for exploring more advanced theories. A considerable effort has been invested here into the clarity and brevity of the presentation. A special feature of this book is in exploring thermomechanical consistency of all presented constitutive models in a simple and systematic manner."

"Penelitian ini bertujuan untuk mengidentifikasi program SPH yang mampu memodelkan fenomena keruntuhan lereng dengan 2 pendekatan SPH yang berbeda dibandingkan untuk mengamati bagaimana perilaku partikel saat mensimulasikan keruntuhan lereng. Program SPH Drucker-Prager dipilih karena mencakup parameter tanah yang diperlukan untuk memodelkan keruntuhan lereng. Program SPH Drucker-Prager dimodifikasi dengan menambahkan efek gravitasi pada partikel yang meningkatkan perilaku partikel. Tekanan Isotropik, Densitas dan Viskositas Semu dalam Program SPH yang dimodifikasi dianalisis untuk memeriksa apakah sesuai dengan kondisi yang diharapkan. Analisis visual menunjukkan bahwa partikel mampu memadat namun belum mampu menunjukkan perilaku keruntuhan lereng yang diharapkan. Analisis variabel dasar menunjukkan bahwa nilai yang dihitung oleh program SPH umumnya lebih besar dari nilai yang diharapkan. Program SPH yang dipilih membutuhkan modifikasi tambahan pada kode sebelum mampu memodelkan keruntuhan lereng. Modifikasi tersebut melibatkan peningkatan algoritma untuk menstabilkan Tekanan Isotropik ketika partikel berinteraksi dengan batas dan jenis partikel yang berbeda dan penambahan Metode Pengurangan Kekuatan.

---

This research aims to identify the SPH program that is capable of modelling the phenomena of slope failure 2 different SPH approaches were compared to observe how the particles behave when simulating slope failure. The Drucker-Prager SPH program was selected as it includes the necessary soil parameters to model slope failure. The Drucker-Prager SPH program was modified by adding the effects of gravity on the particles improving the behaviour of the particles. The Isotropic Pressure, Density and Apparent Viscosity in the modified SPH Program were analysed to check whether it conforms to the expected conditions. The visual analysis showed that the particles are capable of compacting however is not yet capable of showing the expected slope failure behaviour. The analysis of base variables shows that the values computed by the SPH program generally are greater than the expected values. The chosen SPH Program needs additional modifications to the code before it is capable of modelling slope failure. Such modifications involve the improvement of the algorithm to stabilise the Isotropic Pressure when the particles interact with the boundary and different particle types and the addition of the Strength Reduction Method."