RD&D-Programme 2004 - SKB

Newfound knowledge since RD&D 2001
General aspects of the problem of spalling and stability of the deposition hole walls have been
elaborated on in an overview study /19-33/. In particular, the importance of a small support
pressure from the buffer to prevent initiation and propagation of failure that can lead to
spalling is discussed. Background material is the theory of brittle failure developed at AECL’s
Underground Rock Laboratory (URL) in Canada.
A compilation of geological, mechanical and thermomechanical parameter values for the rock
mass around the Apse experiment has been published as a basis for prediction of the occurrence
of spalling under thermomechanical loading of the Apse pillar /19-45/.
A preliminary BEM analysis of the Apse experiment has been done with the code Examine3D
in a feasibility study /19-34/. The elastic Examine3D model cannot be used to simulate failure,
but comprises a basis for assessing which areas can enter a failure state and can therefore be a
platform for the development of models where failure and fracture propagation are modelled
explicitly with, for example, Fracod or Particle Flow Code.
Preliminary 3D results have been obtained from thermomechanical Flac3D simulations of the
Apse experiment /19-46/. The results are based on an elastic material model, but give, like the
Examine3D study, indications of the stresses and how they may compare with levels that are
relevant for brittle failure.
The results of thermomechanical JobFem simulations, with sensitivity analyses, have also
been obtained for a horizontal two-dimensional section through the centre of the pillar’s height
/19-47/.
A BEM code, Fracod, for calculation of fracturing has been further developed and applied to the
Apse pillar /19-48/.
Programme
The problem of coalescence of individual fractures (on a 100-metre scale) will be addressed in
calculation projects for reactivation. Furthermore, different methods for representing the effects
of fracture propagation on large single fractures will also be tested. One of the objectives is
to investigate to what extent fracture movements at large loads can be limited because strain
energy is consumed by fracture propagation. A preliminary model already exists for this /19-49/,
but an improved and more systematic analysis is needed.
The Apse experiment will be completed and evaluated. The technique for modelling of brittle
failure and fracture propagation will be developed, in part by further applications with Fracod
and in part by means of new calculation tools and methods. Different types of models will be
docked to a coherent analysis. Areas that may enter a failure state, for example areas adjacent to
the deposition hole wall in the Apse experiment, are represented by PFC (Particle Flow Code)
models, while rock outside such areas is represented by continuum models. In addition, there
has been recent progress in the application of the PFC code to stress-induced failure by simulation
of the entire failure curve for both tensile and compressive stresses /19-105/.
19.2.9 Time-dependent deformations
Conclusions in RD&D 2001 and its review
It was stated in RD&D 2001 that the handling of creep movements in rock had so far been based
on conservative estimates, or boundings, of possible effects on the geometry of the cavities.
The authorities have not made any comments on this process.
254 RD&D-Programme 2004