The fluid-flow and geomechanical processes near excavations in rock are inherently coupled through alteration of the fluid-flow parameters of permeability and porosity due to mechanical damage induced by the excavation. In addition, the mechanical stresses which drive the rock damage may be altered by fluid pore pressure. The coupling is especially significant in the halitic material which contains the Waste Isolation Pilot Plant (WIPP) due to salt creep into the open excavations. This work focuses on developing a coupled fluid-flow and mechanical model which includes this coupling effect in order to analyze WIPP repository performance. The coupled model, TEJAS, utilizes the fluid-flow code TOUGH28W/EOS8 and the mechanical code JAS3D.
L'ecoule~ent des fluides et les processus geomecaniques presents à proximite des excavations rocheuses sont fondamentalement lies au travers des changements des paramètres d'ecoulement, permeabilite et porosite, engendres par les dommages dus à l'excavation. Les contraintes mecaniques qui affectent la masse rocheuse peuvent egalement alterer la pression des fluides. Ce couplage est particulièrement important dans les formations salifères qui renferment le WIPP à cause du fluage du sel dans les espaces ouverts. Ce travail s'attache à developper un modèle qui couple ecoulement des fluides et mecanique des roches afin d'analyser la performance du WIPP. Le modèle, TEJAS. utilise le programme d'ecoulement des fluides, TOUGH28W/EOS8 et le programme geomecanique. JAS3D.
Strömungs- und geomechanische Prozesse im Nahbereich von Gesteinsaushöhlungen im Untergrund sind ueber die Änderungen der Fliessparameter Permeabilitat und Porositat gekoppelt, hervorgerufen durch die mechanische Beanspruchung des Gesteins beim Stollenvortrieb. Auf der anderen Seite wird der mechanische Stress, der die Gesteinsverformung verursacnt, durch den Porenwasserdruck verandert. Diese Koppelung is besonders signifikant in Salzgesteinen wegen dem plastischen Verhalten von Salz in offenen Kavernen, in dem die WIPP (Pilotanalage fuer Abfalleinlagerung) konzipiert ist. Der Schwerpunkt dieser Studie liegt in der Entwicklung eines gekoppelten strömungs- und geomechanischen Modells, welches diese gekoppelten Prozesse beruecksichtigt, urn eine sicherheitstechnische Bewertung des WIPP Endlagers durchzufuehren. Dafuer wurde das gekoppelte numerische. Program TEJAS entwickelt, welches das Zweiphasentluss-Program TOUGH28W/EOS8 und das geomechanische Program JAS3D benutzt.
The Waste Isolation Pilot Plant (WIPP) is a United States Department of Energy (DOE) facility located in southeastern New Mexico for underground disposal of transuranic waste. The facility has been excavated from the bedded salts of the Salado formation at a depth of approximately 655 m below ground surface. The Permian-age Salado formation is approximately 600 m thick at the WIPP site and is composed primarily of bedded halite with laterally continuous interbeds of anhydrite, poly-halite, clay and siltstone. The underground waste storage system is composed of eight panels each containing seven waste disposal rooms approximately 4 m high, 10m wide. and 91 m long.
The WIPP repository design is intended to prevent stored waste, contaminants from reaching the accessible environment for as long as the waste remains hazardous. The applicable regulatory period for analysis of repository performance is 10,000 years. An important part of the analysis of the long-term performance of the waste disposal system is an understanding of the hydraulic response of the repository/host rock system under the natural fluid pressure gradients which exist in the vicinity of the WIPP repository.
