BARIK: an extended Hoek–Brown-based anisotropic constitutive model for fractured crystalline rock
Authors: León Vargas Rocio Paola , Friedel Max , Hassanzadegan Alireza , Rahmig Michael , Weber Fabian , Konietzky Heinz 
Published: September 2023

Abstract. The disposal of heat-generating radioactive waste in deep
geologic formations is a global concern. Numerical methods play a key role
in understanding and assessing the disposal scenarios of radioactive waste
in deep geological repositories. However, the complexities of the thermal,
hydrological, mechanical, chemical, and biological processes associated with
the disposal of radioactive waste in porous and fractured materials
constitute significant challenges. One of the most challenging issues in
this field is the complex material behavior of fractured crystalline rock.
The presence of fractures makes the rock anisotropic, nonlinear, and
dependent on loading paths. Additionally, the Biot coefficient cannot be
considered constant throughout the critical and subcritical fracture
development regions. These factors make the development of an accurate
constitutive model for fractured crystalline hard rock a critical component
of any deep geological disposal project. Furthermore, to demonstrate the
integrity of the containment-providing rock zone in crystalline host rock,
the qualitative integrity criteria must be quantified so that numerical
simulation can be performed with concrete numerical values. Part of this
assessment for a crystalline host rock is a dilatancy criterion, which is
currently based on the Hoek–Brown constitutive model. BARIK is the German acronym for the research project on which this paper is based. This contribution provides an overview of the development and verification
of the BARIK constitutive model, an extended Hoek–Brown model for fractured
crystalline hard rock that takes into account up to three fracture systems.
The model enables the consideration of the matrix and joint behavior of the
rock separately, with each component having unique strength characteristics
and failure criteria. These criteria are formulated such that suitable
consideration of the strength-reducing properties of the respective fracture
systems during barrier integrity verification is possible. The BARIK model
has been implemented into two computer codes, FLAC3D and MFront for
OpenGeoSys, allowing for the identification and evaluation of any
inaccuracies that may arise from the use of different codes. The model
enables isotropic–elastic, orthotropic–elastic, isotropic–elasto-plastic,
and orthotropic–elasto-plastic calculations of the matrix, making it a
valuable tool for the site selection process and for the construction and
long-term safety of underground repositories. Furthermore, this poster
presentation will show how the constitutive model was evaluated in relation
to the dilatancy criterion and how the BARIK constitutive model's
suitability for conducting an integrity assessment was validated. In
conclusion, the development of BARIK is a significant step forward in the
understanding and modeling of the complex material behavior of fractured
crystalline hard rock. This contribution will provide insights into the
development and verification of this model for the safe disposal of
radioactive waste.