Extension of biaxial highpressure test system

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The device applied for is a further development and improvement of an existing biaxial test system into a test system for true triaxial compressive loading. Following the concept of the biaxial test system, prismatic specimens in the triaxial test system will loaded through six steel plates. It is well known that the intermediate principal stress has a decisive influence on the deformation and strength behaviour of rocks. Both, primary stress states in the earth's crust and secondary stress states in the sphere of influence of cavities and underground structures are generally strongly anisotropic. Experimental reproduction of these loading boundary conditions on a laboratory scale is therefore of central importance when situations and conditions characterized by great anisotropy are investigated. Since in conventional triaxial tests (Karman-type) two principal normal stresses are always the same, the influence of the mean principal normal stress cannot be investigated with this technique.A testing device for true triaxial compressive loads is currently not available either at the TU Bergakademie Freiberg or at institutions with which research cooperations exist. Therefore, our working group has no access to such testing technology and cannot deal with highly topical research topics associated with it. Central aspects in the choice of the type of construction of the true triaxial testing device were the following: Flexible choice of size of prismatic specimens from 100 to 300 mm edge length Realization of large compressive stresses (up to 200 MPa depending on specimen size) Possibility of dynamic loading in all axes (e.g. cyclic loading, earthquake signal or singular impact) Continued possibility of biaxial testing with good monitoring possibilities Coupling of sensors for deformation measurement and piezoceramic sensors directly via the pressure plates Realization of a homogeneous stress and deformation field in the test specimenThe equipment will be used in research projects on the following topics: Development and testing of an extended hydro-mechanical-coupled Hoek-Brown failure criterion for the assessment of anisotropic strength behaviour when applied to fracture of crystalline rocks Stability of deep geothermal wells in granite Behaviour of fractured rock under triaxial loading Mountain formation processes / Experimental modeling of selected orogenesis processes with rocks and equivalent materials