Disturbed zone modelling SVC validation drift using UDEC-BB, models 1 to 8 - Stripa phase 3

Several rock mechanics studies were performed within the site characterization and validation (SCV) project at Stripa. Joints represented in Harwell's stochastically generated 8m x 8m x 8m cubes were used to select four possible joints geometries for two-dimensional rock mechanics simulations of the 2.8 x 2.2 m validation drift, and the rock mass response to its excavation. The joints intersecting the four end faces of these cubes were set up in distinct element UDEC-BB models, and loaded with boundary stresses of 10 MPa vertically and 14 to 18 MPa horizontally. In numerical models 1, 2, 3 and 4 average values of the Barton Bandis joint parameters JRC, JCS and φr were utilized for all joints, irrespective of length. These values were obtained from NGI's index characterization of 220 joints in 100 mm core and from 200 mm diameter and 1 x 1 2m block testing were coupled closure-shear-flow testing (CSFT) was also performed. In numerical models 5, 6, 7, 8 the same joint geometries were utilized with length-dependent values of JRC, JCS and φr. The longest joints were given low values representing mineralized persistent discontinuities, while the shortest joints were given high values. Detailed analyses were made of the tangential and radial stress magnitudes that were obtained in the four UDEC-BB discontinuum models 5, 6, 7 and 8. Results were presented for all sectors of the models as a function of radius from the drift walls. These stress magnitudes were compared with those from an equivalent continuum model which showed, as expected, much more predictable stress gradients. Modelled drift closures ranged from 2 to 3 mm in the jointed models and from 1 to 1.5 mm in the continuum model. Local tensile stress development maximum 28 MPa, and local shearing of individual joints, maximum 1.0 mm, were a feature of the jointed models. Peak tangential stresses locally reached 54 to 74 MPa in the jointed models compared to 43 MPa in the continuum model. (au)