Fractures finite element codes

Abstract This contribution deals with the modeling of coupled thermal (T), hydraulic (H) and mechanical (M) processes in subsurface structures or barrier systems. We assume a system of three phases a deformable fractured porous medium fully or partially saturated with liquid and a gas which remains at atmospheric pressure. Consideration of the thermal flow problem leads to an extensively coupled problem consisting of an elliptic and parabolic-hyperbolic set of partial differential equations. The resulting initial boundary value problems are outlined. Their finite element representation and the required solving algorithms and control options for the coupled processes are implemented using object-oriented programming in the finite element code RockFlow/RockMech. 

Rutqvist, J., Bbrgesson, L., Chijimatsu, M., Nguyen, T.S., Jing, L., Noorishad, J., and Tsang, C.-F. lODVo.Coupled Thermo-hydromechanical Analysis of a Heater Test in Fractured Rock and Bentonite at Kamaishi Mine - Comparison of Field Results to Predictions of Four Finite Element Codes. Int. J. Rock mech. Min. Sci. 38 pp. 129-142. 

Chan, T. Guvanasen, V. and Stanchell, F.W. 2003. Verification and validation of a three-dimensional finite-element code for coupled Thermo-Hydro-Mechanical and Salinity (T-H-M-C) modelling in fractured rock mass. This conference. 

VERIFICATION AND VALIDATION OF A THREE-DIMENSIONAL FINITE-ELEMENT CODE FOR COUPLED THERMO-HYDRO-MECHANICAL AND SAUNITY (T-H-M-C) MODELLING IN FRACTURED ROCK MASSES... 

Abstract motif is a three-dimensional finite-element code developed to simulate groundwater flow, heat transfer and solute transport in deformable fractured porous media. The code has been subjected to an extensive verification and updating programme since the onset of its development. In this paper, additional verification and validation works with an emphasis on thermo-hydro-mechanical processes are presented. The verification results are based on cases designed to verify thermo-hydro-mechanical coupling terms, and isothermal and non-isothermal consolidations. A number of validation case studies have been conducted on the code. Example results are repotted in this paper. 

The MOTIF code is a three-dimensional finite-element code capable of simulating steady state or transient coupled/uncoupled variable-density, variable- saturation fluid flow, heat transport, and conservative or nonspecies radionuclide) transport in deformable fractured/ porous media. In the code, the porous medium component is represented by hexahedral elements, triangular prism elements, tetrahedral elements, quadrilateral planar elements, and lineal elements. Discrete fractures are represented by biplanar quadrilateral elements (for the equilibrium equation), and monoplanar quadrilateral elements (for flow and transport equations). 

The six verification tests presented in this paper, along with other verification tests presented in the cited literature, have established the ability of the MOTIF finite-element code to accurately solve the equations of groundwater flow, solute and heat transport, and coupled thermo-hydro-mechanical phenomena in porous media, or in fractured media that can be adequately characterized by equivalent porous media (EPM) elements or a combination of EPM and discrete fracture elements. 

Recognizing the importance of the coupled hydro-mechanical effects on the performance of civil engineering structures involving fractured rocks, the stress-flow coupling mechanism of the dam-foundation system at Longyangxia site was simulated using a three-dimensional Finite Element code, supported by two visco-elastic constitutive models to represent the time-dependent material behaviour of the dam concrete and the foundation rock. The calculated results were concord with the measured ones and helped to interpret the causes of this continuous displacement at the 13" dam section of the Longyangxia hydropower project, towards the left bank. 

FRAC2D Finite Element Code for 2D and Axisymmetric Fracture Analysis, General Electric Global Research, Niskayuna, NY... 

Four research teams—AECB, CLAY, KIPH and LBNL—studied the task with different computational models. The computer codes applied to the task were ROCMAS, FRACON, THAMES and ABAQUS-CLAY. All of them were based on the finite-element method (FEM). Figure 6 presents an overview of the geometry and the boundary conditions of respective models, including the nearfield rock, bentonite buffer, concrete lid, and heater. The LBNL model is the largest and explicitly includes nearby drifts as well as three main fractures... 

Although these three criteria specify different aspects, they all yield similar results and no experimentally distinguishable differences have been observed [2,3,11,12]. Consequently, the choice of criterion in practical applications depends on convenience. The maximum opening stress and the maximum strain energy release rate criteria are often used in analytical studies, whereas the mode I fracture criterion is usually more convenient to use in numerical analysis since standard stress intensity factor extrapolation schemes are usually available in most commercial finite element analysis (FEA) codes. All three criteria are consistent with the mechanics notion that cracks tend to grow perpendicular to the largest tensile stress. 

For the hydraulic phase, each discontinuity is considered to be crossed by a set of channels (ID hydraulic element) generated either deterministically or statistically. At the intersection of two joints, a hydraulic conduit, called a tube, is produced. Flow is limited to fractures and the blocks are impervious. The diffusion equation is resolved throughout the finite differences. Initial conductivities are assigned to both channels and tubes (combined within the denoted pipe). Displacements computed with the 3DEC code influence the conductivity of hydraulic elements by the following relationship ... 

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