Naslov
Rock mechanics, failure phenomena with preexisting cracks and internal fluid flow through cracks
(Rock mechanics, failure phenomena with pre-existing cracks and internal fluid flow through cracks)

Autori
Nikolić, Mijo

Vrsta, podvrsta i kategorija rada
Ocjenski radovi, doktorska disertacija

Fakultet
Fakultet građevinarstva, arhitekture i geodezije

Mjesto
Split

Datum
28.09

Godina
2015

Stranica
107

Mentor
Ibrahimbegović, Adnan ; Miščević, Predrag

Ključne riječi
localized failure; heterogeneous materials; embedded discontinuity; method of

Sažetak
This thesis deals with the problem of localized failure in rocks, which occurs often in civil engineering practice like in dam failure, foundation collapse, stability of excavations, slopes and tunnels, landslides and rock falls. The risk of localized failure should be better understood in order to be prevented. The localized failure in rocks is usually characterized by a sudden and brittle failure without warning in a sense of larger and visible deformations prior to failure. This happens also under the strong influence of material heterogeneities, pre- existing cracks and other defects. The three novel numerical models, incorporating the localized failure mechanisms, heterogeneity of rock and pre- existing cracks and other defects, are presented in this thesis. First model deals with 2D plane strain two-phase rock composite, where stronger phase represents the intact rock and weaker phase initial defects. Second model represents the extension of the previous model towards the 3D space, where full set of 3D failure mechanisms is considered. Heterogeneous properties are taken here through the random distribution and Gauss statistical variation of material properties. The latter model is also used for the analysis of intact rock core specimens geometrical shape deviations influencing the uniaxial compressive strength. Third model is a 2D, dealing with volumetric fluid-structure interaction and localized failure under the influence of fluid flow through the porous rock medium. The discrete beam lattice approach is chosen for general framework for three models, where Voronoi cells represent the rock grains kept together by Timoshenko beams as cohesive links. The enhanced kinematics characterized for embedded discontinuity approach is added upon standard kinematics of cohesive links. This serves for the macrocrack propagation in all failure modes and their combinations, between the rock grains. The fracture process zone formation followed by micro- cracks coalescence, preceding the localized failure, is considered as well. Fluid flow is governed by a Darcy law, while coupling conditions obey Biot’s theory of poroplasticity. The results of the numerical models were verified by the benchmarks available from literature in 2D case. The 3D model was validated against the experimental results conducted on 90 rock specimens, where even slight geometrical deviations of specimens are considered. Presentation of these models, as well as their implementation aspects are given in full detail. Embedded discontinuity concept and the local nature of enhancements required to capture the displacement discontinuities leads to the very efficient approach with static condensation of enhanced degrees of freedom and technique that can be efficiently incorporated into finite element code architecture.

Izvorni jezik
Engleski

Znanstvena područja
Građevinarstvo

Napomena
Doktorska disertacija izrađena je kao dvojni doktorat u suradnji s DE L’E´COLE NORMALE SUPERIEURE DE CACHAN

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