The octahedral concept and cubic triaxiality in assessment of secondary stress state

Mihaela Toderas¹

¹University of Petrosani, Petrosani, 332006, Romania

Min. miner. depos. 2020, 14(1):81-90

https://doi.org/10.33271/mining14.01.081

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      ABSTRACT

      Purpose. The opportunities offered by rock mechanics as a science are not fully and efficiently applied in the design and assessment of underground constructions performed in salt massifs, especially in the efficient design and long-term lifetime of the geometrical elements that characterize the exploitation method with rooms and pillars. It can be asserted that such a conventional limitation of the possibilities of rock mechanics, is due to some gaps, the lack of a fundamental theoretical – experimental theory regarding the three-dimensional behavior of the rock mass.

      Methods. The mechanical behavior of the salt was studied under triaxial conditions. The conventional triaxial method was supplemented with a three-dimensional analysis  –  of salt massif and of rooms and pillars exploitation complex by cubic triaxiality. The deformation behavior of the salt was studied through the assessment of both cylindrical triaxial and cubic triaxial.

      Findings. Analytically, based on the cubic triaxial experiments according to the octahedral concept, deformation and rheological properties of salt, results that a salt massif can be characterized in terms of the natural stress state value, by three types of zones: stable, transition and unstable.

      Originality.Based on the octahedral geomechanical parameters, an analytical model for the characterization of salt massifs has been proposed, a model that has been verified both by laboratory research by the instrumentality of modelling and also by in situ measurements. In this context, it resulted that for the analyzed salt with the highest resistance, the octahedral strength does not exceed 5.6 MPa and, therefore, it is dangerous to use in the salt mines field design values of 2 to 5 times higher than the real value.

      Practical implications. The determination of stress – deformation natural state is related to the highlighting of the contour or limits of the zones situated in a certain state (in triaxial context) with the consideration of the determinative anisotropy, namely, of strength and deformation anisotropy, as well as of the rheological behavior of in situ salt.

      Keywords: octahedral concept, triaxiality, stress state, pillar, salt, rheology, interaction

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