The Yucca Mountain Site Characterization Project is conducting a drift-scale heater test, known as the Drift Scale Test (DST), in an alcove of the Exploratory Studies Facility at Yucca Mountain, Nevada. We have developed a drift-scale distinct element model (DSDE) and are using the model to analyze the geomechanical response of the rock mass forming the DST. We simulated the DST as both a continuum and a fractured rock mass. The fractures incorporated in the simulations were derived from a fracture data set mapped using borehole televiewer logs. We have compared predicted deformation to deformation measured in the DST using multiple point borehole extensometers (MPBX). Preliminary analysis shows that simulated deformations for both continuum and discontinum models generally match the magnitude of the measured deformations. The simulations generally underpredict the deformation during the first year of heating, indicating that the thermal model used for the simulations needs improvement. Results show that a thermal expansion coefficient of 4 x10-?/øC may be appropriate for the
fractured rock mass.
The Yucca Mountain Site Characterization Project is conducting a drift scale heater test, known as the Drift Scale Test (DST), in an alcove of the Exploratory Studies Facility (ESF) at Yucca Mountain, Nevada. The DST is a large-scale, longterm thermal test designed to investigate coupled thermal-mechanical-hydrological-chemical (TMHC) behavior in a fractured, densely welded ash-flow tuff (Datta et al. 1999).
Moreover, fluid movement in this rock is thought to occur primarily through the fractures. Our work is concerned with describing fracture deformation due to thermal mechanical effects, as normal and shear deformation of fractures can substantially change the fracture permeability, and affect the coupled TMHC behavior.
A drift-scale distinct element model (DSDE) is being used to analyze the geomechanical response of the rock mass forming the DST. The distinct element method was chosen to permit explicit modeling of fracture deformations. Shear deformations and normal mode opening of fractures are expected to increase fracture permeability and thereby alter thermal-hydrologic behavior in the DST. We have collected fracture data for a subset of boreholes in the DST and have used these data in the formulation of the DSDE model of the test. This paper presents a brief discussion of the model formulation, along with results of the first phase of our analysis, which is a preliminary comparison of simulated and observed deformations at selected locations within the test.