Papers by George Exadaktylos
Journal of the Mechanical Behavior of Materials, 2005
A simple hierarchical methodology is proposed herein for back-analysis of in situ closure measure... more A simple hierarchical methodology is proposed herein for back-analysis of in situ closure measurements in tunnels that is based on in situ convergence measurements, the equivalent plane strain concept, analytical and numerical modeling of continuous elastic and elasto-plastic rocks and dimensional analysis. An example of the application of the proposed methodology is given for the Tempi high-speed railway tunnel in Greece. It is demonstrated that both the in situ lateral-to-vertical stress ratio, rock mass deformation modulus and cohesion are indirectly inferred from the proposed data-inversion analysis, which in turn may be used for future design of tunnels in similar geotechnical conditions. It is also shown that deformation modulus of the rock mass exhibits size effect and stress-dependency, hence the in situ stress ratio depends on the deformation modulus. 2. INTRODUCTION Rock mass deformability and cohesion are important input parameters for the estimation of the appropriate tunnel excavation sequence and shape, as well as support pressure, since they affect the rock mass displacements and strength. Moreover, of all quantities that the undergound excavation engineer is required to estimate or to measure while undertaking any major underground excavation stability problem, the in situ or pre-excavation stress field in a rock mass is one of the most difficult. The vertical stress can be approximated, to an acceptable level of accuracy, by the product of the depth below surface and the unit weight of the rock mass. The latter, with a good level of accuracy, may be taken as equal to 0.027 MN/m that in turn gives an average stress gradient of 0.027 MPa/m /!/. On the other hand, according to the well
Rock Mechanics and Rock Engineering
The spacing distribution of natural joints or fractures in rock masses affects the rock mass defo... more The spacing distribution of natural joints or fractures in rock masses affects the rock mass deformability, strength and transport properties according to their size, distribution in space, deformability and strength. Rock block sizes formed by intersecting joints are also an important engineering parameter influencing the behavior of rock masses around underground openings and surface excavations, extraction of blocks of commercial sizes of decorative stones and in rock fragmentation processes by blasting or mechanical excavation techniques. The rock block shapes and sizes are depicted by the number of joint sets, as well as orientation in space, persistence and spacings of joint sets transecting the rock mass. In this paper, we first elaborate on a new generalized Poisson probability density function of joint frequencies counted along scanlines and boreholes. Based on this probability density function we construct an algorithm for the estimation of joint spacings distribution from joint frequency measurements along scanlines. The validation of the conversion of joint frequencies to joint spacings is performed with the Monte-Carlo simulation technique. Joint count data along with drill cores from a white dolomitic marble quarry transected by three joint sets is used to demonstrate the application of the proposed algorithm. The proposed model and associated algorithm are necessary for the subsequent prediction of rock block volume distribution isolated between mutually intersecting joints. In this context among other applications they may find many applications in Discrete Fracture Network (DFN) modelling of jointed rock masses.
Mining
The island of Cyprus is famous for its rich deposits of volcanic mineralisation that yielded larg... more The island of Cyprus is famous for its rich deposits of volcanic mineralisation that yielded large quantities of copper, gold, and silver. The abandonment of the waste material in several dump sites during exploitation severely impacted the environment. A significant environmental issue is the acid mine drainage from the hydration of large barren piles that cover these old open pit mines. However, abandoned piles are still enriched in precious metals and perhaps even rare earth metals. These dump sites may form a new possible “deposit”, which may attract companies’ economic interest. Removing the stockpiles can be cost-effective, since the secondary extraction process is profitable, in addition to the benefits from the restoration of the natural environment. The case study considered here pertains to the North Mine of Mathiatis, where unmanned aerial vehicle (UAV) images were used to create not only a 3D topographic map but also to locate these dump sites and finally to create a 3D ...
International Journal of Materials and Product Technology, 2006
Abstract: The damage,of either intact or notched,marble,beams,under bending is studied with both ... more Abstract: The damage,of either intact or notched,marble,beams,under bending is studied with both destructive and non-destructive techniques, in an effort to assess the reliability of the non-destructive methods,in the case of rock-type materials. The specimens are made from Dionysos marble, the material used for the restoration of the Parthenon Temple of the Acropolis of Athens. The experimental,results for the intact specimens,are
Coupled Systems Mechanics, 2013
This document describes the “INSPIRE data specification on Natural Risk Zones – Guidelines” versi... more This document describes the “INSPIRE data specification on Natural Risk Zones – Guidelines” version 2.0 as developed by the Thematic Working Group (TWG) Natural Risk Zones using both natural and a conceptual schema language. This version is now available for the public consultation. Based on the results of the consultation (received comments and the testing reports), the final version 3.0 will be prepared by the TWGs. The data specification is based on a common template used for all data specifications and has been harmonised using the experience from the development of the Annex I data specifications. This document provides guidelines for the implementation of the provisions laid down in the draft Implementing Rule for spatial data sets and services of the INSPIRE Directive. This document includes two executive summaries that provide a quick overview of the INSPIRE data specification process in general, and the content of the data specification on Natural Risk Zones in particular. ...
286 Abstract— Aiming at developing a flexible IT tool that will enable someone to have fast acces... more 286 Abstract— Aiming at developing a flexible IT tool that will enable someone to have fast access to strength and other useful properties of structural damageable materials by using appropriate queries through the internet, we have developed a relational web driven database accompanied by a modeling tool that is developed n Mathworks Matlab. The database and the accompanying matlab tool aims at fast approximate calculations of the behavior of a certain structural material element under a given hazard intensity or under repeated cycles of loading.
GML «FeatureType» feature::AbstractFeature + boundedBy :GM_Envelope [0..1] NOTE : If the exposed ... more GML «FeatureType» feature::AbstractFeature + boundedBy :GM_Envelope [0..1] NOTE : If the exposed element spatial object is provided with a spatial representation, then the object does not have to be linked to any other spatial object defined in another INSPIRE theme. If the exposed element spatial object is NOT provided with a spatial representation, then it shall reference another object defined in another INSPIRE theme by using this association. /*If the "source of spatial representation" is empty, the geometry AbstractExposedElement spatial object shall be provided.*/ inv: AbstractExposedElement.sourceOfSpatialRepresentation. isEmpty() implies ExposedElements.geometry.notEmpty() +isMonitoredBy «voidable»
ABSTRACT Complex variable representations for Dirichlet and Neumann boundary value problems of fa... more ABSTRACT Complex variable representations for Dirichlet and Neumann boundary value problems of faulting in poroelastic geologic media that may be analytically or numerically solved in space domain (steady state), have been developed. The benefits of this complex variable formulation is first that stress equilibrium and compatibility relations are automatically satisfied, secondly we may use the results already developed in classical elasticity theory, thirdly we may effectively take into account singularities such as fault tips, and finally we reduce the considerably the computing time and memory. This semi analytical model will be used as a tool for back-analysis and understanding of the underlying basic mechanisms in (i) downhole hydraulic fracturing stress measurements (back-analysis of hydrofracturing results in order to evaluate the in situ stresses and stress variation with depth in regions exhibiting normal faulting), and (ii) for the study of interaction and activation of normal faults and pore pressure changes in faulted regions such as the Gulf of Corinth. Numerical results for the distribution of stresses and pore pressure around curved poroelastic faults will be presented.
Le Journal de Physique IV, 1998
ABSTRACT
Mining, Metallurgy & Exploration
International Journal for Numerical and Analytical Methods in Geomechanics
International Journal of Rock Mechanics and Mining Sciences
International Journal of Solids and Structures
ABSTRACT This document describes the “INSPIRE data specification on Natural Risk Zones – Technica... more ABSTRACT This document describes the “INSPIRE data specification on Natural Risk Zones – Technical Guidelines” version 3.0 as developed by the Thematic Working Group (TWG) Natural Risk Zones using both natural and a conceptual schema language.
Sustainable development in the mineral industry requires a paradigm shift from purely economic to... more Sustainable development in the mineral industry requires a paradigm shift from purely economic to multi-objective decision-making, considering economic, social, environmental and governance criteria. The commonly accepted aim is responsible stewardship of non-renewable re-sources. State-of-the-art 3D geological and mine modeling software technology can contribute to meet this objective as reliable and accurate geological models form the basis for an optimum management. The benefits obtained by the application of computerized modeling are illustrated at hand of three studies. The examples cover global and local producers of industrial minerals in fully developed as well as development countries. They refer to different levels of planning, from initial resource assessment over long-term planning to the generation of rolling forecast for operative planning in a running mine.
Bifurcations, Instabilities, Degradation in Geomechanics, 2007
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Papers by George Exadaktylos