numgeo: A finite-element program for the simulation of hydro-mechanically coupled geotechnical processes (original) (raw)
Related papers
International Journal for Numerical and Analytical Methods in Geomechanics, 2003
This paper presents a complete finite-element treatment for unsaturated soil problems. A new formulation of general constitutive equations for unsaturated soils is first presented. In the incremental stress-strain equations, the suction or the pore water pressure is treated as a strain variable instead of a stress variable. The global governing equations are derived in terms of displacement and pore water pressure. The discretized governing equations are then solved using an adaptive time-stepping scheme which automatically adjusts the time-step size so that the integration error in the displacements and pore pressures lies close to a specified tolerance. The non-linearity caused by suction-dependent plastic yielding, suction-dependent degree of saturation , and saturation-dependent permeability is treated in a similar way to the elastoplasticity. An explicit stress integration scheme is used to solve the constitutive stress-strain equations at the Gauss point level. The elastoplastic stiffness matrix in the Euler solution is evaluated using the suction as well as the stresses and hardening parameters at the start of the subincrement, while the elastoplastic matrix in the modified Euler solution is evaluated using the suction at the end of the subincrement. In addition, when applying subincrementation, the same rate is applied to all strain components including the suction.
A non-linear numerical model for soil mechanics
International Journal for Numerical and Analytical Methods in Geomechanics, 1992
A new computer program (CONBAL-2) is developed for 2D numerical simulations of granular soil by random arrays of spheres. CONBAL-2 uses the discrete-element method and is based on 3D program TRUBAL, previoudy presented by Cundall. As in TRUBAL, the new program models a random array of elastic spheres in a periodic space. The main modification of TRUBAL is the implementation by the authors of a rigorous solution for the force-displacement relation at the interparticle contacts. This force-displacement relation is a function of the elastic constants, friction coefficient and sizes of the spheres, with the properties of quartz used to simulate sand. Other specific features of CONBAL-2 include its 2D character, the lack of particle rotation and its capability to simulate shear loading on any plane. Simulated laboratory test results are presented using CONBAL-2 and several random arrays of 531 spheres having two particle sizes. These simulations include monotonic loading drained and undrained (constant volume) 'triaxial' experiments, as well as a cyclic-loading, constant-volume 'torsional shear' test. The stress-strain curves, effective stress paths, volume changes, as well as the 'pore water pressure' build-up behaviour obtained in the simulations compare favourably-qualitatively and in some aspects quantitatively-with similar laboratory results on sands. However, the simulated soil is somewhat stiffer and stronger due to the perfectly rounded particles, limited range of grain sizes, lack of particle rotation and 2D character of the model.
Soil-Structure Interaction Using Computer and Material Models Advanced Geotechnical Engineering
Advanced Geotechnical Engineering: Soil-Structure Interaction using Computer and Material Models , 2010
Soil-structure interaction is an area of major importance in geotechnical engineering and geomechanics Advanced Geotechnical Engineering: Soil-Structure Interaction using Computer and Material Models covers computer and analytical methods for a number of geotechnical problems. It introduces the main factors important to the application of computer methods and constitutive models with emphasis on the behavior of soils, rocks, interfaces, and joints, vital for reliable and accurate solutions. This book presents finite element (FE), finite difference (FD), and analytical methods and their applications by using computers, in conjunction with the use of appropriate constitutive models; they can provide realistic solutions for soil–structure problems. A part of this book is devoted to solving practical problems using hand calculations in addition to the use of computer methods. The book also introduces commercial computer codes as well as computer codes developed by the authors. Uses simplified constitutive models such as linear and nonlinear elastic for resistance-displacement response in 1-D problems Uses advanced constitutive models such as elasticplastic, continued yield plasticity and DSC for microstructural changes leading to microcracking, failure and liquefaction Delves into the FE and FD methods for problems that are idealized as two-dimensional (2-D) and three-dimensional (3-D) Covers the application for 3-D FE methods and an approximate procedure called multicomponent methods Includes the application to a number of problems such as dams , slopes, piles, retaining (reinforced earth) structures, tunnels, pavements, seepage, consolidation, involving field measurements, shake table, and centrifuge tests Discusses the effect of interface response on the behavior of geotechnical systems and liquefaction (considered as a microstructural instability) This text is useful to practitioners, students, teachers, and researchers who have backgrounds in geotechnical, structural engineering, and basic mechanics courses.
Evaluation of three‐and two‐field finite element methods for the dynamic response of saturated soil
1994
The three-field formulation up -U is presented and is applied to solve dynamic equations for saturated porous media. In order to evaluate the accuracy and the performance of this three-field approximation, the u-U and the u-w formulations are also considered and a few one-and two-dimensional examples are solved using the three methods. Problems for which both the pore fluid and the solid grains are incompressible are also considered and are solved using the up U approximation. Accuracy was determined by a comparison of the finite element results with the analytical solution given by Gajo and Mongiovi," for a wide range of permeability.
Finite element formulation and algorithms for unsaturated soils. Part I: Theory
2003
This paper presents a complete finite-element treatment for unsaturated soil problems. A new formulation of general constitutive equations for unsaturated soils is first presented. In the incremental stress-strain equations, the suction or the pore water pressure is treated as a strain variable instead of a stress variable. The global governing equations are derived in terms of displacement and pore water pressure. The discretized governing equations are then solved using an adaptive time-stepping scheme which automatically adjusts the time-step size so that the integration error in the displacements and pore pressures lies close to a specified tolerance. The non-linearity caused by suction-dependent plastic yielding, suction-dependent degree of saturation , and saturation-dependent permeability is treated in a similar way to the elastoplasticity. An explicit stress integration scheme is used to solve the constitutive stress-strain equations at the Gauss point level. The elastoplastic stiffness matrix in the Euler solution is evaluated using the suction as well as the stresses and hardening parameters at the start of the subincrement, while the elastoplastic matrix in the modified Euler solution is evaluated using the suction at the end of the subincrement. In addition, when applying subincrementation, the same rate is applied to all strain components including the suction.
Numerical simulation of centrifuge tests on homogeneous and heterogeneous soil models
Computers and Geotechnics, 2012
Soil liquefaction is a major cause of seismic damage in cohessionless soil during earthquakes. From past numerical and experimental research it has been observed that more excess pore water pressure (EPWP) is generated during earthquakes in a heterogeneous soil deposit than in the corresponding homogeneous soil with relative density equal to the average relative density of the heterogeneous soil. This interesting phenomenon is investigated here, by numerically simulating centrifuge experiments of seismically induced soil liquefaction using the finite element code DYNAFLOW. Two centrifuge tests are numerically simulated here: one in homogeneous soil and another in heterogeneous soil. Recorded experimental results such as accelerations, EPWP and settlements are compared with the simulated numerical results. Numerically simulated and recorded results support the conclusions of previous research that more EPWP is generated in a heterogeneous soil deposits than in the corresponding homogeneous soil.
Geosciences
Unsaturated soil is a three-phase medium with three interfaces, and the mathematical equations that represent its behavior must be developed in a fully coupled manner for accurately predicting its hydromechanical behavior. In this paper, a set of fully coupled governing equations was developed for the dynamics of unsaturated soil, considering the interaction among the bulk phases and interfaces. In addition to implementing the complete governing equations, a simplified formulation was developed for practical applications. The derivation of the finite element formulation considering all the terms in the partial differential equations resulted in a formulation called complete formulation and was solved for the first time in this paper. Another formulation called reduced formulation was derived by neglecting the relative accelerations and velocities of water and air in the governing equations. In addition, small and large deformation theories were developed and implemented for both for...
Coupled solid-fluid FE-analysis of geotechnical problems involving partially saturated soils
GAMM-Mitteilungen, 2010
A numerical model for coupled solid-fluid FE-analyses of geotechnical problems involving partially saturated soils is described. As constitutive model for partially saturated soil serves the Barcelona Basic Model, which is formulated in terms of net stress and capillary pressure. Different stress update algorithms are compared for this model regarding the accuracy and efficiency. The application of the numerical model is demonstrated by numerical simulations of the impoundment of an earth dam and of the injection of compressed air into water saturated soil.
Development of coupled numerical model for simulation of multiphase soil
Computers and Geotechnics
In this paper, a coupled multiphase model considering both non-linearities of water retention curves and solid state modeling is proposed. The solid displacements and the pressures of both water and air phases are unknowns of the proposed model. The finite element method is used to solve the governing differential equations. The proposed method is demonstrated through simulation of seepage test and partially consolidation problem. Then, implementation of the model is done by using hypoplasticity for the solid phase and analyzing the fully saturated triaxial experiments. In integration of the constitutive law error controlling is improved and comparisons done accordingly. In this work, the advantages and limitations of the numerical model are discussed.