Kaare Høeg

Parametric study for a large cavern in jointed rock using a distinct element model (UDEC—BB)

Parametric studies are performed using the distinct element computer program UDEC—BB for a large cavern in the Himalayas. The studies provide insights into some important deformation mechanisms in a numerical system of blocks. The sensitivity studies involving changes in joint spacings (block size) revealed that the deformations around an opening are dependent on the size or the number of blocks adjacent to the excavation. Large size blocks deform mainly through translational shear upon which rotational shear may occur. In a model in which the block size is small compared to the tunnel dimensions, the tendency to dilation across an increased number of non-planar joints may contribute to interlocking of blocks. The BB joint behavioural model, which allows the modelling of the dilation accompanying shear and hence the build-up of higher normal stresses, predicts smaller deformations than the Mohr—Coulomb model in which the dilation angle is constant. The sensitivity studies involving changes in key BB joint shear strength parameters have shown that, within the range of values considered, the model output is relatively insensitive to assumed joint strength parameters joint roughness coefficient and r. However, an increase in the joint wall compressive strength contributes to an increase in the joint shear strength resulting in a marked reduction of displacements around the opening.

Numerical modelling of block size effects and influence of joint properties in multiply jointed rock

Abstract Two-dimensional numerical experiments are conducted for investigating the effects of block size and joint properties on the behaviour of multiply jointed rock. The paper explains how the size of the individual blocks controls both the shear strength of the assembly (rock mass) and its deformational characteristics. A closely jointed rock mass, in which block rotations occur, exhibits a lower stiffness but a higher strength than a roch mass with widely spacedjoints. These numerical results are similar to those from reported physical model tests on jointed slabs of a rock model material. The paper shows how parametric studies on a single joint using the Barton-Bandis (BB) formulation are useful for providing information about the response of a jointed rock mass.