NUMERICAL TREATMENT OF PROGRESSIVE LOCALIZATION IN RELATION TO BOREHOLE STABILITY

Results of large-scale finite element computations are presented for the problem of borehole failure due to the high stresses at great depths. Rock is modelled by an extension of the Mohr-Coulomb flow theory of plasticity for material with Cosserat micro-structure. The introduction of internal length (grain size) improves the computational stability and allows for robust post-localization computations. The presented results show clearly a progressive failure mechanism and the computed failure modes are in a good qualitative agreement with laboratory and field observations.