Hydro-Mechanical Coupling in Zero-Thickness Interface Elements, Formulation and Applications in Geomechanics

AbstractZero-thickness joint/interface elements of the Goodman type, have been advantageously used to solve many problems in solid mechanics involving material interfaces or discontinuities. Some years ago, the authors have also proposed a version of such element for flow/diffusion and hydro-mechanical (H-M) coupled problems, either geomechanical or multiphysics. Some advantages are for instance that fluid pressure discontinuities and localized flow lines may be represented on the same FE mesh used for the mechanical problem, as well as the influence of fluid pressure on mechanical stresses or, conversely, of crack openings on the flow redistribution (“cubic law”). In the paper, previous developments are briefly described, together with some new Geomechanical applications under development, particularly the application to the hydraulic fracture problems, which in the past have been studied mainly via analytical or semi-analytical formulations, or using mixed FE-FD approaches.IntroductionInterface or joint elements of zero-thickness type (Goodman et al. 1968), have been successfully used to solve many problems in solid mechanics involving material interfaces or discontinuities. These elements are inserted in between standard elements to allow jumps in the solution field. Their kinematic constitutive (“strain-type”) variables are relative displacements, and the corresponding static (“stress-type”) variables are stress tractions. In particular, the authors have used them for representing rock joints in the context of rock masses, contacts between soil and steel reinforcement in reinforced earth structures, or cracks in concrete or other quasibrittle materials, etc. (Gens et al. 1995, Caballero et al. 2007). Each application requires different constitutive laws, either frictional-type (Gens et al. 1990) or fracture-based with elasto-plastic structure (Carol et al. 1997). Some years ago, the authors have also proposed a version of such element for flow/diffusion, either of geo-mechanical (Segura & Carol 2004) or multiphysics type (Idiart et al. 2011). Some advantages are for instance that fluid pressure discontinuities and localized flow lines may be represented on the same FE mesh used for the mechanical problem, as well as the influence of fluid pressure on mechanical stresses or, conversely, of crack openings on the flow redistribution (“cubic law”). More recent developments include advanced “monolithic” implementation (Segura & Carol 2004), return map algor