Large-scale geomechanical model testing of an underground cavern group in a true three-dimensional (3-D) stress state

The stability of a large cavern group at great depth is discussed on the basis of large-scale three-dimensional (3-D) geomechanical model tests and numerical simulations. The model tests are described in detail. Improvements in the tests were made in terms of experimental techniques and advanced measurement methods. The model tests utilized active loading on six sides of a rock mass in a true 3-D stress state. During the model construction, precast blocks were fabricated and monitoring holes were defined prior to test initiation. Newly developed combination ball-sliding walls were installed on each of the major loading surfaces to reduce the friction induced by model deformation. A unique grouting and installation technique employing prestressed cables was adopted in the tests. A digital photogrammetric technique, displacement sensing bars using fiber Bragg grating (FBG) technology, and mini multipoint extensometers were developed for measuring deformation. Overloading tests were then conducted for different overburden depths, and 3-D numerical analyses were performed to simulate the testing procedures. Conclusions regarding the stability of the cavern group were developed based on a comparison between the experimental and numerical results. Key words: geomechanical model test, numerical simulation, large-scale underground cavern group, true 3-D stress state, stability analysis. La stabilite d'un groupe de grandes cavemes profondes est discutee en utilisant des essais en modele geomecanique 3-D a grande echelle et des simulations numeriques. Les essais sont decrits en details dans l'article. Des ameliorations ont ete apportees aux essais par rapport aux techniques experimentales et aux methodes de mesures. Les essais component des chargements actifs sur 6 faces d'une masse de roche de faeon a representer un etat des contraintes en 3- D. Durant la construction du modele, des blocs pre-moules ont ete fabriques et des ports de suivi ont ete definis avant le debut des essais. Sur chacune des surfaces majeures de chargement, des murs en combinaison bille-glissement recemment developpes ont ete installes afin de reduire la friction induite par les deformations du modele. Une technique de scellemenl el d'installation unique utilisant des cables precontracts a ete ulilisee durant les essais. Une technique photogrammetrique digitale, des sondes de displacements munies de la technologie d'un reseau de fibre Bragg, et de minis extensiometres multi-points ont ete developpes afin de mesurer les deformations. Des essais en surcharge ont ete effectues pour des profondeurs de mort-terrain differentes. Ensuite, des analyses numeriques en 3-D ont ete effectives dans le but de simuler les procedures de l'essai. Des conclusions en lien avec la stabilite du groupe de cavemes ont ete developpees selon des comparaisons entre les resultats experimentaux et numeriques. Mots-cles : essai en modele geomecanique, simulation numerique, groupe de grandes cavemes souterraines, etat des contraintes 3-D reel, analyse de stabilite. [Traduit par la Redaction]
Introduction Due to the dramatic global increase in urbanization, underground caverns have become an attractive option for the construction of powerhouses, transportation conduits, energy storage facilities, and municipal utility systems. [...]