The stability of jointed rock masses around underground cavities depends on discontinuities geometry, in situ stresses, joints characteristics and in less degree on the mechanical properties of intact rock. The aim of this paper is to present, for a given geometry, the influence of joint constitutive laws upon the stability of an underground excavation at different depths. All results were obtained using the program U.D.E.C. in which we have implemented Amadei's constitutive model of rock joints.


La stabilite des excavations souterraines dans un massif rocheux fracture depend de la geometrie des discontinuites, des contraintes in situ, des caracteristiques des joints et dans un moindre degre, des proprietes mecaniques de la roche intacte. Le but de ce papier est de presenter, pour une geometrie donnee, l'influence des lois de comportement des joints sur la stabilite d'une cavite souterraine en fonction de la profondeur. Tous les resultats ont ete obtenus en utilisant le code U.D.E.C. dans lequel nous avons implante le modèle constitutif d'Amadei relatif aux joints rocheux.


Sicherheit von Undertagedeponien in geklufteten Gebirgskörpers ist abhangig von Kluftgeometrie, in situ Spannung, Kluftparameters und in einem geringe Maβ von mechanischer Verhalten des unverritztem Gestein. Dieser Artikel stellt fuer eine gewisse Geometrie, der Einfluβ des Kluftverhaltengesetzen an die Sicherheit eine Untertagedeponie abhangig der Tiefe. Alle presentierende Resultaten sind mit U.D.E.C. Kode herausgefunden in dem Amadei constitutiv Modell relativ zu Gesteinkluften eingefuehrt ist.


Design analysis of underground excavations involves determination of stresses and displacements in the rock mass surrounding the cavity. Any excavation in jointed rock usually involves slip and separation along discontinuities as well as translation and/or rotation of rock blocks. The discret element method is a numerical method for simulating the behavior of a jointed rock mass or, in general, the behavior of an assembly of discrete blocks. This method was first proposed by Cundall (1971). In particular, Cundall and Hart (1985, 1989) developped the Distinct Element Method which is part of the discrete element methods. The distinct element method assumes a discontinuous medium in order to simulate the behavior of jointed rock masses subjected to quasi-static or dynamic conditions. The method has three characteristics: 1. The rock mass is regarded as an assembly of blocks which interact through discontinuities (joints). 2. Discontinuities are regarded as boundary interactions between these blocks. The spring slider systems prescibe force-displacement relations between blocks. 3. The method utilizes an explicit time step algorithm which allows large displacements and rotations. The blocks can be rigid or deformable. All results shown here were obtained using the bidimensional program Universal Distinct Element Code (U.D.E.C) Cundall and Hart (1985, 1989) in which we have implemented the non-linear Amadei's constitutive model of rock joints. The aim of this paper is to present, for a given discontnuities geometry, the influence of joint constitutive laws upon the stability of an underground cavity for different depths.


In the commercial version of UDEC which was used, there are two constitutive laws of jointed rock:

  1. The elastic/plastic with Mohr-Coulomb failure (law 1).

  2. The continuously-yielding joint model (law 2) proposed by Cundall and Hart 1985 and revised by Lemos 1987, which simulates the intrinsic mechanism of progressive damage of joints under shear. We have implemented in this version of UDEC the Saeb and Amadei (1990) and Amadei and Saeb (1992) constitutive model (law 3). The behavior in normal direction is linear for law 1 and 2, contrary to the law 3 whose normal stress vs normal closure curve is hyperbolic as it can be observed from laboratory tests (Bandis and Barton 1983).

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