A Study of Swelling Behaviour in a Tunnel Using Finite Element Methods

The aim of this research is to show swelling behaviour in a tunnel excavated through rocks by modeling them and using laboratory results. The engineering challenge is how to design a tunnel which contains swelling rocks such as marl. This aim is achieved through two methods. In the first method, the Field System Solution program (FISS) is calibrated using experimentally obtained laboratory graphs of the saturated rocks around the tunnel, and the parameters are applied to the geometry of the tunnel. Comparing a critical state model with stresses around the tunnel, stability of the rocks was examined. In the second method, stability of the rocks around the tunnel was investigated by using the Nisa-II program, adjusting the laboratory swelling graphs with the creep function to the program and, finally, drawing Von Mises stresses around the tunnel

Numerical Analysis of Sand Behavior based on Modified Multi-laminate Model

Generalized form of multi-laminate integration framework satisfying compatibility of strain/deformation and equilibrium of stress/forces at each material point was employed to sum up the plastic modulus matrices of integrated planes to build up the main modulus matrix. This has been conducted through defining on plane modulus behaviors for normal, tangent and their interactions for loading and unloading. This modulus formulation enables the analysis to include the role of some material behavior aspects in the overall internal plasticity mechanism flexibility for a more accurate description of mechanism behavior under any arbitrary loading conditions. Specification of stress/strain history on the sample planes in materials with the models developed using stress/strain invariants is not feasible. This is mainly because stress/strain invariants are quantities not capable of carrying directional information with themselves. In this article, a constitutive model capable of predicting sand behavior under static and dynamic loading working with stress and strain invariants was modified and implemented in the multi-laminate framework to be capable of predicting any arbitrary stress path may take place on a sand element in soil structure. The proposed model is capable of presenting different stress/strain histories on the sample planes followed the applied load/deformation paths in soil materials. Model verification under different loading/unloading/reloading stress/strain paths has been examined and failure direction of sand samples was visualized upon the activities of on plane plastic strain values and then exceeding a certain limit, specified as failed plane. This constitutive model can be used to predict the sand behavior upon inherent/induced anisotropy, rotation of principal stress/strain axes, localization of stress/strain and even failure mechanism

A hybrid numerical model for multiphase fluid flow in a deformable porous medium

In this paper, a fully coupled finite volume-finite element model for a deforming porous medium interacting with the flow of two immiscible pore fluids is presented. The basic equations describing the system are derived based on the averaging theory. Applying the standard Galerkin finite element method to solve this system of partial differential equations does not conserve mass locally. A non-conservative method may cause some accuracy and stability problems. The control volume based finite element technique that satisfies local mass conservation of the flow equations can be an appropriate alternative. Full coupling of control volume based finite element and the standard finite element techniques to solve the multiphase flow and geomechanical equilibrium equations is the main goal of this paper. The accuracy and efficiency of the method are verified by studying several examples for which analytical or numerical solutions are available. The effect of mesh orientation is investigated by simulating a benchmark water-flooding problem. A representative example is also presented to demonstrate the capability of the model to simulate the behavior in heterogeneous porous media

Evaluation of the three constitutive models to characterize granular base for pavement analysis using finite element method

Abstract: Resilient modulus is an important input for computation of the structural response of pavements in Mechanistic -Empirical Methods. It has a significant effect on computed pavement responses and predicted pavement performance. The main objective of the research study that is introduced here is to develop a material model subroutine applicable to Finite Element program to simulate the nonlinear behavior of unbound granular materials, and evaluate the influence of using different constitutive models for characterization of unbound granular materials on critical responses of Flexible pavements. These constitutive models include Linear Elastic, Uzan and Universal models. For this purpose, three different pavement sections are assumed and FE models for these sections were verified by comparing elastic responses with KENLAYER Program. A granular base with known material constants for these three models was selected and sections were analyzed using different constitutive models. The results indicate that the selection of a proper nonlinear model has a significant effect on prediction of pavement responses and so on predicted performance of pavement