Coupled hm analysis using zero-thickness interface elements with double nodes

Coupled hydro-mechanical (HM) processes in pre-existing discontinuities (geological) and developing cracks (fractures) are important in many fields of engineering (e,g. Dams, Oil or Environmental). In these situations, flow through the discontinuity is influenced by its deformation through changes in the permeability and the storage capacity. At the same time, changes in fluid pressure result in changes in the effective stress distribution, and the subsequent closure, opening or even propagation of the discontinuity. The problem becomes more complicated when the medium that contains the discontinuity is porous, since fluid exchange between both may appear and HM coupling must be considered also in the porous domain. The thesis formulates the HM coupled problem in jointed or susceptible of fracturing geomaterials by means of the Finite Element Method (FEM) with "zero-thickness" interface elements and double nodes to discretize and describe the HM behavior of discontinuities. Each element (continuum and interface) is formulated in terms of the displacements (u) and the fluid pressure (p) at nodes. After assembly, a particular expression of the traditional "u-p" system of coupled equations is obtained, which is highly non-linear due to the strong dependence between the permeability and the aperture of discontinuities. Poro-elasticity is assumed in the continuum. The cubic law is considered to govern the longitudinal flow along an open discontinuity, whereas for a closed or filled discontinuity Darcy's law can be used along the plane. The influence of a transversal potential drop is introduced by means of a transversal transmissivity that takes into account the existence of impermeable material within a discontinuity. The constitutive model that relates effective stresses to relative displacements in the interface depends on the type of problem being analyzed (pre-existing joint: rock mechanics based model; developing crack: fracture mechanics based model). The "u-p"