En la actualidad, son cada vez mas las canteras de roca ornamental ?explotadas tradicionalmente a cielo abierto? que, debido a condicionantes de tipo tecnico, ambiental, social o economico, estan planteando la posibilidad de ser explotadas mediante labores de interior. Este es el caso de Pizarras Gallegas, S.A. que, en colaboracion con el grupo de Ingenieria del Terreno de la Universidad de Oviedo, esta llevando a cabo una serie de proyectos de investigacion para determinar la idoneidad de explotar su yacimiento de pizarra del Barco de Valedoras (Orense) mediante laboreo subterraneo. En este articulo se describen las caracteristicas del proyecto.
Cracking due to desiccation can compromise the behaviour of earth structures built with compacted clayey soils by promoting water access and consequent volume changes on further wetting. Tensile strength therefore is important to be considered when studying the behaviour of such structures, and in particular its dependence on the degree of saturation or water content. The influence of water content in tensile behaviour of compacted marls was investigated by performing diametral compression tests (Brazilian splitting tests), where axial deformations were measured besides strength. The samples were prepared by compaction at optimum point using standard compaction energy (optimum water content 16%) and then dried by vapour equilibrium to reach water contents between 5% and 16%. The correspondence between water content and suction was done by using the drying branch of the water retention curve, measured using WP4 equipment (Water Dewpoint Potentiometer). Good relationships were found between tensile strength and the water content (and suction). In addition, the study was completed with the analysis of other parameters such as the semi-contact angle created in the loaded area and the stiffness of the material, which also showed changes with water content.
This paper shows the possibility that the mineral coal existing in the mining basins of northern Spain have a high added value.This would facilitate its future use in different fields such as new materials, nanotechnology, energy use in situ, coal bed methane, enhanced coal bed methane and coalmine methane.An analytical study of mineral coal samples is carried out.The samples come from two deposits located in coal basins of the Cantabrian Mountains.The duly prepared samples are subjected to an activation process.Within this transformation, different treatments are applied to different sub-samples.Some of the sub-samples suffer a previous demineralization by successive attacks with acids, followed by oxidation and pyrolysis.Finally, all of them are activated with CO 2 and H 2 O (steam) .The carbonaceous products resulting from each treatment are characterised.The results show that all the pre-treatments used were positive for the textural development of the materials.Likewise, proper management of the processes and of the different operating variables allows the procurement of carbonaceous materials with a "tailor-made" structural development of the coal type.This material receives the name "activated" and can be employed in specific processes.
Being thermal coal such an abundant resource in Spain, we are looking for alternative uses for it. This would enable its future use in different fields, same of them already classic, such as: new materials (graphene, activated carbon, molecular sieves, etc.), nano-technology, in situ energy use (gasification and liquefaction), CBM (coal bed methane), ECBM (coal bed methane with CO2 injection) and CMM (coal mine methane). It could also be used in other innovative areas with high added value, such as gastronomy and biomedicine.
In the present research a new non-lineal failure criterion in rocks called GIT criterion is established. The new criterion has been developed by the Ground Engineering Group from the University of Oviedo (Spain), and it can be expressed in terms of both normal and shear stresses (σn,τ), and principal stresses (σ3, σ1 ). Three characteristic parameters define the criterion, which are estimated applying nonlinear least squares regression methods, using the Levenberg-Marquardt (LM) algorithm. The novelty of this new criterion is that its determination can be carried out only by using uniaxial compression tests, which are more economic and easier to implement than triaxial tests. The theoretical formulation is accompanied by set laboratory tests, and the results obtained are compared with the classical criteria employed in rock mechanics, such as those of Mohr-Coulomb and Hoek-Brown.
Due to the heterogeneity of rocks, their tensile strength is around 10% of their compressive strength, which means that breakage is mainly caused by tensile stress. The measure of tensile stress is very difficult due to rock fragility, so it has usually been measured by indirect measurement methods , including the Brazilian test. However, recent works indicate that the tensile strength values obtained through the Brazilian test must be increased by almost 26%. To understand this divergence, indirect tensile tests have been monitored. The aim is to know the material deformation and load increase by means of stepwise regression. Stress fields in slightly deformed samples are analyzed and modeled (3D finite differences) with loads applied on flat and curved plates and different Young's modulus. Finally, the results are analyzed and compared with strength values reported using Timoshenko theory and Hondros' approximation.
