INFLUENCE OF TECTONIC DISTURBANCES OF COAL LAYER ON HIS GAS DYNAMIC STATE

Problem Statement and Purpose. At one of the coal mines of the Donetsk basin, there was a sudden release of coal and gas. The peculiarity of this case is that the accident happened in the place of the alleged development of a geological disturbance, but without any visible signs of this. Inspection of the ejection site and adjacent horizons made it possible to conclude that the emergency site is located in the place of the plicative disturbance development. Thus, it is necessary to study in more detail the influence of disturbed zones hidden nature on the gas-dynamic state of the reservoir, as well as to develop and implement methods for determining such zones. Data & Methods. To achieve this goal, a new method was tested, based on the property of structureless substances to form crystal-like units. This phenomenon has been studied for decades; therefore, such new formations have long been given the name quasicrystals. It was noted that the increase in the concentration of such forms is associated with the presence of geological disturbances. Consequently, the increase in quasicrystals in the rock is an indicator of its disturbance due to the influence of tectonic pressure. Thus, in order to test the technique and reveal the hidden geological disturbance of the coal seam, coal samples were taken, microstructural features were studied, and the strength of the coal seam was measured at 56 points. Result. As a result the values of the concentration of quasicrystals, data on the strength of the formation were obtained, a schematic map of the development of the disturbance in this area was built, its contours were determined, the center of the disturbed zone was identified and the role of such disturbances in the outburst hazard of the formation was substantiated. It has been established that geological disturbances, even of plicative nature, have a high degree of fracturing. Such pores and cracks in coal reduce the strength properties and are able to concentrate sufficient volumes of gas for manifestation of GDP.

Reaction and Alteration of Mudstone with Ordinary Portland Cement and Low Alkali Cement Pore Fluids

The construction of a repository for the geological disposal of radioactive waste will utilize cement-based materials. Following closure, resaturation will result in the development of a highly alkaline porewater. The alkaline fluid will migrate and react with host rock, producing a chemically disturbed zone (CDZ) around the repository. To understand how these conditions may evolve, a series of batch and flow experiments were conducted with Horonobe mudstone and fluids representative of the alkaline leachates expected from a cementitious repository. Both ordinary Portland cement (OPC) and low alkali cement (LAC) leachates were examined. The impact of the LAC leachates was more limited than the OPC leachates, with experiments using the LAC leachate showing the least reaction and lowest long-term pH of the different leachate types. The reaction was dominated by primary mineral dissolution, and in the case of OPC leachates, precipitation of secondary calcium-silicate-hydrate (C-S-H) phases. Flow experiments revealed that precipitation of the secondary phases was restricted to close to the initial contact zone of the fluids and mudstone. The experimental results demonstrate that a combination of both batch and flow-through experiments can provide the insights required for the understanding of the key geochemical interactions and the impact of transport.

Understanding dilatancy in rocksalt: a microphysical model of rocksalt at the grain-scale

<p>The use of underground repositories excavated in low-permeability formations, such as rock salt, to store high-level, radioactive waste requires the analysis of its isolation properties. Underground excavation disturbs the original stress state of the rocksalt, resulting in a deviatoric stress distribution around the walls of excavated galleries and boreholes. At high deviatoric stresses and low confinement, dense rocksalt produces an increase in porosity and permeability. The extent of dilatancy in this disturbed zone, as well as the impact of dilatancy on the transport properties, are important for assessing the safety of radio-active waste disposal as well as the integrity of salt caverns and boreholes in the context of energy storage, brine cavern abandonment and gas well abandonment.  </p><p>The stress conditions at which dilatancy occurs have been measured experimentally, and are typically determined on the basis of macroscopic (sample-scale) measurements of volumetric strain and permeability, and/or acoustic velocity changes or emissions. However, the detailed mechanisms causing dilatancy at the grain-scale are poorly understood. We have developed a microphysical model for dilatancy in rocksalt, both under dry and wet conditions, including mechanisms such as slip and opening of grain boundaries. This model enables us to describe and predict the dilatancy behaviour of rocksalt based on physical, mechanical and chemical processes. The model is presently being independently verified through comparison with existing literature data, and new experiments.</p>

New Records of Polymita venusta (Gmelin, 1792) Populations in Northern Foothills of Sierra de Boniato, Santiago de Cuba Province

Three new localities of Polymita venusta are uncovered from the northern foothills of Sierra de Boniato in the Santiago de Cuba province. In those, five new populations inhabiting fragmented forests over karstic substratum were found between 238-405 meters above sea level. The rediscovery of a unique color form took place in one colony from the La Luz vicinity. These populations occupy a highly deforested area where the main activities are cattle grazing and agriculture, combined with other anthropic threats. Protected Areas planning for this human highly disturbed zone is nonexistent.

Calculation Method of Underground Cavern Loosening Pressure Based on Limit Analysis Using Upper-Bound Theory and Its Engineering Application

From the point of view of the failure mechanism of the disturbed zone, this paper uses the limit analysis upper-bound theory to analyze the calculation formula of the loosening pressure, distinguish the difference between the vertical pressure and the horizontal pressure in the underground cavern, combine the loosening characteristics of the disturbed zone with the open-type disturbed zone and the annular disturbed zone, and construct the multirigidity slider translation and rotation failure mode to discuss the calculation method of surrounding rock loosening pressure of underground caverns in upper soft and hard rock stratum. The relevant calculation examples are given, and the application of the upper-bound theory of limit analysis is demonstrated in detail. Based on the actual engineering background, the calculation results of the calculation method of the loosening pressure of the cavity based on the upper-bound theory of the limit analysis are analyzed and compared for the different depths and different types of caverns. The difference, rationality, and applicability of the calculation results of this method are analyzed and discussed.

Prediction of Damage Level of Slab-Column Joints under Blast Load

The behavior of a slab-column joint subjected to blast loads was studied by numerical analysis using a general-purpose finite element analysis program, LS-DYNA. Under the explosive load, the joint region known as the stress disturbed zone was defined as a region with a scaled distance of 0.1 m/kg1/3 or less through comparison with ConWep’s empirical formula. Displacement and support rotation according to Trinitrotoluene (TNT) weight and scaled distance were investigated by dividing in and out of the joint region. In addition, fracture volume was newly proposed as an evaluation factor for blast-resistant performance, and it was confirmed that the degree of damage to a member due to blast loads was well represented by the fracture volume. Finally, a prediction equation for the blast-resistant performance of the slab-column joint was proposed, and the reliability and accuracy of the equation were verified through additional numerical analysis.