Energies

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16 pages, 5197 KiB

Open AccessArticle

Experimental Study on the Effect of Temperature on the Mechanical Properties of Unconsolidated Silty Sandstones

by Juan Alejandro Arias-Buitrago, Guillermo A. Alzate-Espinosa, Alejandra Arbelaez-Londoño, Gonzalo Zambrano-Narvaez and Rick Chalaturnyk

Energies 2021, 14(21), 7007; https://doi.org/10.3390/en14217007 - 26 Oct 2021

Cited by 3 | Viewed by 1344

Abstract

Hydrocarbon reservoirs can be subjected to temperature changes due to different processes during production. Heat injection has become an advantageous method to produce heavy oils in Canada and Venezuela because it increases oil recovery. The heat reduces oil viscosity and oil flows easily. [...] Read more.

Hydrocarbon reservoirs can be subjected to temperature changes due to different processes during production. Heat injection has become an advantageous method to produce heavy oils in Canada and Venezuela because it increases oil recovery. The heat reduces oil viscosity and oil flows easily. Colombia has significant heavy oil reserves in unconsolidated silty sandstones. It is important to understand the mechanical behavior of these reservoirs in thermal recovery conditions (temperature and effective stress). The reconstituted samples from a Colombian heavy oil outcrop were evaluated using a high-temperature and high-pressure triaxial cell. Twelve isotropically consolidated drained triaxial tests were conducted at three different effective stresses (0.4, 4.0, and 8.2 MPa) and a temperature range from 50 to 230 °C to represent the initial and thermal recovery conditions, and obtain parameters, such as Young’s and Bulk moduli, internal friction angle, and cohesion. The samples at higher confining stress (4.0 and 8.2 MPa) were under contraction, while samples at lower confining stress (0.4 MPa) were under dilation. The stiffness increased as the confining stress increased and decreased as temperature increased, and the strength properties significantly decreased as temperature increased. Finally, the Colombian samples exhibited low friction angles when compared to clean sandstones as Canadian sands. Full article

(This article belongs to the Special Issue Geomechanics for Energy)

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18 pages, 2534 KiB

Open AccessArticle

An Attempt to Use Machine Learning Algorithms to Estimate the Rockburst Hazard in Underground Excavations of Hard Coal Mine

by Łukasz Wojtecki, Sebastian Iwaszenko, Derek B. Apel and Tomasz Cichy

Energies 2021, 14(21), 6928; https://doi.org/10.3390/en14216928 - 21 Oct 2021

Cited by 17 | Viewed by 2268

Abstract

Rockburst is a dynamic rock mass failure occurring during underground mining under unfavorable stress conditions. The rockburst phenomenon concerns openings in different rocks and is generally correlated with high stress in the rock mass. As a result of rockburst, underground excavations lose their [...] Read more.

Rockburst is a dynamic rock mass failure occurring during underground mining under unfavorable stress conditions. The rockburst phenomenon concerns openings in different rocks and is generally correlated with high stress in the rock mass. As a result of rockburst, underground excavations lose their functionality, the infrastructure is damaged, and the working conditions become unsafe. Assessing rockburst hazards in underground excavations becomes particularly important with the increasing mining depth and the mining-induced stresses. Nowadays, rockburst risk prediction is based mainly on various indicators. However, some attempts have been made to apply machine learning algorithms for this purpose. For this article, we employed an extensive range of machine learning algorithms, e.g., an artificial neural network, decision tree, random forest, and gradient boosting, to estimate the rockburst risk in galleries in one of the deep hard coal mines in the Upper Silesian Coal Basin, Poland. With the use of these algorithms, we proposed rockburst risk prediction models. Neural network and decision tree models were most effective in assessing whether a rockburst occurred in an analyzed case, taking into account the average value of the recall parameter. In three randomly selected datasets, the artificial neural network models were able to identify all of the rockbursts. Full article

(This article belongs to the Special Issue Geomechanics for Energy)

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19 pages, 5417 KiB

Open AccessArticle

Mining-Induced Seismicity during Development Works in Coalbeds in the Context of Forecasts of Geomechanical Conditions

by Dariusz Chlebowski and Zbigniew Burtan

Energies 2021, 14(20), 6675; https://doi.org/10.3390/en14206675 - 14 Oct 2021

Cited by 8 | Viewed by 1676

Abstract

Mining-induced seismicity in the area of development works and proper mining operations is one of the major determinants of the rockburst hazard level in underground mines. Rockburst hazard assessment in Polish collieries is performed by a variety of mining and geophysical methods, including [...] Read more.

Mining-induced seismicity in the area of development works and proper mining operations is one of the major determinants of the rockburst hazard level in underground mines. Rockburst hazard assessment in Polish collieries is performed by a variety of mining and geophysical methods, including seismic and seismoacoustic techniques, borehole surveys, small diameter drilling, rock strata profiling and analyses of geomechanical properties of rocks, geological structure and geological mining conditions. In the case of zones particularly exposed to potential hazards, it is recommended that analytical or numerical forecasts of the state of stress in the vicinity of workings should be used already at the stage of planning of mining operations. This study summarises the comparative analysis of seismic test data and analytical forecasts of the state of stress in five selected headings in one of the burst-prone collieries within the Upper Silesia Coal Basin in Poland (USCB). As regards the seismic data, duly defined quantitative indicators and energy criteria of the registered seismic activity are recalled in the assessment of rockburst hazard level during the roadheading operations. Analytical simulations utilise a developed geomechanical model and stress–strain relationships stemming from the principles of elastic media mechanics. From the standpoint of mining engineering practice, interpretation of results obtained by the two methods reveals how effective analytical models will be in prognosticating or verification of rockburst hazard conditions. Full article

(This article belongs to the Special Issue Geomechanics for Energy)

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25 pages, 8541 KiB

Open AccessArticle

A Modified Resonant Column Device for In-Depth Analysis of Vibration in Cohesive and Cohesionless Soils

by Piotr E. Srokosz, Ireneusz Dyka, Marcin Bujko and Marta Bocheńska

Energies 2021, 14(20), 6647; https://doi.org/10.3390/en14206647 - 14 Oct 2021

Cited by 4 | Viewed by 1394

Abstract

With the accelerating progression of global climate change, switching to renewable energy sources is inevitable. Wind energy is a fast-growing branch of this industry, and according to the 2021 Global Wind Report, this trend must continue in order to limit the increase in [...] Read more.

With the accelerating progression of global climate change, switching to renewable energy sources is inevitable. Wind energy is a fast-growing branch of this industry, and according to the 2021 Global Wind Report, this trend must continue in order to limit the increase in global average temperature. While onshore wind turbines still dominate and account for most recent growth, offshore wind turbines are becoming a promising alternative for geographical, power density-related or even aesthetic reasons. Offshore wind turbines are subjected to more complex loading conditions and proper foundation design is very challenging, however, this is crucial for ensuring and maintaining the structure’s reliability. Soil dynamic tests are one of the bases for wind turbine foundation design. Technical regulations in many countries require such tests to be carried out in a Resonant Column (RC). In this study, a modification of the RC sensors and data acquisition system was introduced in order to conduct in-depth analysis of vibrating soil specimens. The new set of sensors contained five additional accelerometers (Analog Devices ADXL345) attached to the surface of a soil specimen that was subjected to dynamic loading. These accelerometers sent the data to a new data acquisition system, an ARM microcontroller with software developed by authors. The software was able to process test results synchronously with the original software of the RC device. Additionally, the load control system was supplemented with a current pulse generator, which makes it possible to observe the propagation of high-frequency mechanical waves in the tested materials. The modified dynamic testing equipment allowed for the measuring of accelerations and displacements at specific selected points located along the height of the sample, with sampling frequency more than three times higher than that offered by the sensors originally built into the RC device. As a result, some additional dynamic phenomena (i.e., disturbances in the uniformity of vibrations of non-cohesive materials, specimen–device contact imperfections) were observed in the tested soil specimens which remained undetected in standard RC test. Full article

(This article belongs to the Special Issue Geomechanics for Energy)

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28 pages, 4890 KiB

Open AccessArticle

Influence of the Variability of Compressed Air Temperature on Selected Parameters of the Deformation-Stress State of the Rock Mass Around a CAES Salt Cavern

by Krzysztof Polański

Energies 2021, 14(19), 6197; https://doi.org/10.3390/en14196197 - 28 Sep 2021

Cited by 5 | Viewed by 1525

Abstract

The article presents the results of a numerical simulation of the deformation-stress state in the rock mass around a salt cavern which is a part of a CAES installation (Compressed Air Energy Storage). The model is based on the parameters of the Huntorf [...] Read more.

The article presents the results of a numerical simulation of the deformation-stress state in the rock mass around a salt cavern which is a part of a CAES installation (Compressed Air Energy Storage). The model is based on the parameters of the Huntorf power plant installation. The influence of temperature and salt-creep speed on the stability of the storage cavern was determined on the basis of the three different stress criteria and the effort of the rock mass in three points of the cavern at different time intervals. The analysis includes two creep speeds, which represent two different types of salt. The solutions showed that the influence of temperature on the deformation-stress state around the CAES cavern is of importance when considering the stress state at a distance of less than 60 m from the cavern axis (at cavern diameter 30–35 m). With an increase in cavern diameter, it is possible that the impact range will be proportionately larger, but each case requires individual modeling that includes the shape of the cavern and the cavern working cycle. Full article

(This article belongs to the Special Issue Geomechanics for Energy)

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42 pages, 5782 KiB

Open AccessArticle

A Method to Increase the Leaching Progress of Salt Caverns with the Use of the Hydro-Jet Technique

by Mariusz Chromik and Waldemar Korzeniowski

Energies 2021, 14(18), 5833; https://doi.org/10.3390/en14185833 - 15 Sep 2021

Cited by 3 | Viewed by 2147

Abstract

For the storage of hydrocarbons, hydrogen, or other products, underground caverns left over from the exploitation of salt deposits, or made specifically for this purpose, are successfully used. This article analyses the effectiveness of currently used well-leaching technologies in terms of the possibility [...] Read more.

For the storage of hydrocarbons, hydrogen, or other products, underground caverns left over from the exploitation of salt deposits, or made specifically for this purpose, are successfully used. This article analyses the effectiveness of currently used well-leaching technologies in terms of the possibility of increasing the speed of obtaining industrial brine, better control of the shape of the created cavern, and, as a result, a shorter production time. An innovative solution was proposed, which consisted of creating appropriate niches in the walls of the leach well using the high-pressure hydrojet technique, just before the start of the sump leaching. A series of numerical simulations of the technologies were performed for various combinations of niche locations along the well, determining the successive phases of the formation of the cavern space at individual stages and the brine concentration increments for the two assumed technology scenarios. As a result of the modified technology, the possibility of creating a sump with a volume greater than 17%, compared to the classical method carried out at the same time, was indicated. The resulting sump also had a better shape to partially eliminate the reduction in leaching efficiency due to the accumulation of insoluble matter at the bottom. In addition, the brine obtained according to the modified technology had a 15% higher concentration than in the classical method. Full article

(This article belongs to the Special Issue Geomechanics for Energy)

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16 pages, 5433 KiB

Open AccessArticle

Non-Destructive Acoustical Rock Bolt Testing System with Intelligent Filtering in Salt Mine ‘Wieliczka’

by Krzysztof Lalik, Ireneusz Dominik, Paweł Gut, Krzysztof Skrzypkowski, Waldemar Korzeniowski and Krzysztof Zagórski

Energies 2021, 14(17), 5522; https://doi.org/10.3390/en14175522 - 3 Sep 2021

Cited by 5 | Viewed by 1940

Abstract

This article presents the application of a self-excited acoustic SAS system for non-destructive testing (NDT) for roof-bolt housings in laboratory and real mine conditions. The proposed system with a filtering mechanism was applied to the J64-27 composite anchors. The conducted tests allowed successful [...] Read more.

This article presents the application of a self-excited acoustic SAS system for non-destructive testing (NDT) for roof-bolt housings in laboratory and real mine conditions. The proposed system with a filtering mechanism was applied to the J64-27 composite anchors. The conducted tests allowed successful confirmation of the usefulness of the system in the detection of rod defects, damage of the mechanism coupling the anchor to the rock mass and testing of the stress state of the anchor itself. The proposed filtering system allowed eliminating the effect of jump change of frequency in the limit cycle of self-excited system. The proposed method is a novel solution for safety diagnostics of bolt housings in mining applications. Full article

(This article belongs to the Special Issue Geomechanics for Energy)

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18 pages, 2629 KiB

Open AccessArticle

The Influence of Rate of Change in Confining and Pore Pressure on Values of the Modulus of Compressibility of the Rock Skeleton and Biot’s Coefficient

by Andrzej Nowakowski

Energies 2021, 14(11), 3056; https://doi.org/10.3390/en14113056 - 25 May 2021

Cited by 8 | Viewed by 1932

Abstract

This work discusses the results of a study of the influence of rates of change of confining pressure on the result of a drained compressibility tests intended to determine the modulus of compressibility of a rock skeleton K_s. A series of [...] Read more.

This work discusses the results of a study of the influence of rates of change of confining pressure on the result of a drained compressibility tests intended to determine the modulus of compressibility of a rock skeleton K_s. A series of cyclical compressibility tests was performed on samples of sandstone soaked in kerosene, for various rates of compression and decompression of the pressure liquid filling the cell and the pore volume of the sample. The studies showed that the deformability of the tested sample was directly proportional to the rate of change of the confining pressure. As a consequence, the value of the K_s modulus and Biot coefficient α decreased with increasing sample load rate. This phenomenon should be attributed primarily to equilibration of the liquid pressure inside the high-pressure cell with the liquid pressure in the sample pore space, caused by filtration of the pore liquid. These phenomena prove that the filtration process impacts the values of the modulus of compressibility of the rock skeleton K_s and of Biot coefficient α determined on the basis of the experiment. This is significant in the context of the use of Biot equations as constitutive equations for a porous rock medium. Full article

(This article belongs to the Special Issue Geomechanics for Energy)

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21 pages, 4736 KiB

Open AccessArticle

Identification of Rock Mass Critical Discontinuities While Borehole Drilling

by Radosław Waloski, Waldemar Korzeniowski, Łukasz Bołoz and Waldemar Rączka

Energies 2021, 14(10), 2748; https://doi.org/10.3390/en14102748 - 11 May 2021

Cited by 10 | Viewed by 2555

Abstract

Modern technologies need more mineral resources for energy generation, metallurgical products, chemicals, and many other uses. These resources are usually extracted from the Earth’s crust. Many engineering underground-space infrastructures are left after mining activity, with their very interesting features such as very large [...] Read more.

Modern technologies need more mineral resources for energy generation, metallurgical products, chemicals, and many other uses. These resources are usually extracted from the Earth’s crust. Many engineering underground-space infrastructures are left after mining activity, with their very interesting features such as very large storage capacities (e.g., for hydrocarbons, hydrogen, radioactive, or other waste), and long-term geomechanical stability. Our original experiments were carried out in the conditions of an underground metal ore mine where typical mobile drilling rigs, additionally equipped with a set of sensors for recording signals as effects of rock–drill interaction were used for the research testing. A series of boreholes with diameters of Ø38 and lengths of up to 9 m in the rock medium were drilled in the “weak” and “strong” rock masses, and the frequency spectra of their signals were analyzed with the use of the fast Fourier transform (FFT) and short-time Fourier transform (STFT) algorithms. According to the proposed idealized theoretical model of the disturbance and the distinctive acceleration value of the drilling characteristic, the location of the critical discontinuities in the roof of the excavation were recognized. The most important advantage of the proposed method is the quantity and objective monitoring method for detection of a critical rock mass defect (discontinuity) that is significant for the potential functionality of underground workings as a potential energy storage room and their reinforcement. Full article

(This article belongs to the Special Issue Geomechanics for Energy)

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21 pages, 9025 KiB

Open AccessArticle

Hard Rock Mining Using Disk Tools Supported by High-Pressure Water Jets in the Aspect of Reducing Energy Consumption

by Krzysztof Kotwica

Energies 2021, 14(9), 2595; https://doi.org/10.3390/en14092595 - 1 May 2021

Cited by 5 | Viewed by 1584

Abstract

The mining of hard rocks by mechanical methods, using cutting tools, is associated with problems such as sparking, dust generation and increased wear. The application of disk tools allows limiting these problems but requires constructing a machine with large dimensions and weight. To [...] Read more.

The mining of hard rocks by mechanical methods, using cutting tools, is associated with problems such as sparking, dust generation and increased wear. The application of disk tools allows limiting these problems but requires constructing a machine with large dimensions and weight. To limit these problems, high-pressure water jets can be applied. The article presents the effects of using this solution in the field and stand tests when mining rocks with a symmetrical disk. The results of the bench tests of high-pressure water jets to support the process of mining with symmetrical disks, carried out at the AGH University of Science and Technology, performed on a unique test stand, which enabled the samples to be mined in a circular trajectory in conditions similar to real ones, are presented. With the use of a dimensional analysis, a theoretical-empirical model was developed to estimate the impact of slots cut by water jets on the tool load and the amount of output as a function of slots spacing and depth. Considering the similarity criteria for the mined rock sample (mechanical properties), it is possible, with the use of this model, to estimate the most advantageous working parameters while hydromechanical mining uses disks on a larger cutting radius. Full article

(This article belongs to the Special Issue Geomechanics for Energy)

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11 pages, 2851 KiB

Open AccessArticle

Surface Deformations Caused by the Convergence of Large Underground Gas Storage Facilities

by Krzysztof Tajduś, Anton Sroka, Rafał Misa, Antoni Tajduś and Stefan Meyer

Energies 2021, 14(2), 402; https://doi.org/10.3390/en14020402 - 12 Jan 2021

Cited by 12 | Viewed by 2398

Abstract

The article presents a method of forecasting the deformation of the land surface over large fields of underground gas storage facilities located in salt caverns. The solution allows for taking into account many parameters characterising the operation of underground gas storage facilities, such [...] Read more.

The article presents a method of forecasting the deformation of the land surface over large fields of underground gas storage facilities located in salt caverns. The solution allows for taking into account many parameters characterising the operation of underground gas storage facilities, such as cavern processes (leaching, enlargement, operational, etc.), their depth, distribution, diameter, shape, and many others. The advantage of the applied method over other available options is the possibility of using it for large fields of caverns while keeping the calculations simple. The effectiveness of the method has been proven for predicted surface subsidence for the EPE field with 114 underground caverns. The hypothesis was compared with the measurement outcomes. Full article

(This article belongs to the Special Issue Geomechanics for Energy)

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14 pages, 4228 KiB

Open AccessArticle

A New Method of Regulation of Loads Acting on the Shaft Lining in Sections Located in the Salt Rock Mass

by Paweł Kamiński

Energies 2021, 14(1), 42; https://doi.org/10.3390/en14010042 - 23 Dec 2020

Cited by 3 | Viewed by 1615

Abstract

Rock salt is characterized by specific geomechanical and rheological properties. Layers of rock salt at depths of over 900 m cause problems with shaft lining deformation. Methods of shaft lining protection used to date (e.g., in the Sieroszowice mine) have not been effective [...] Read more.

Rock salt is characterized by specific geomechanical and rheological properties. Layers of rock salt at depths of over 900 m cause problems with shaft lining deformation. Methods of shaft lining protection used to date (e.g., in the Sieroszowice mine) have not been effective enough. The research presents a patented and copyright protected concept of a shaft lining construction that can be used in rock masses with strong rheological properties and susceptibility to leaching. A high value of convergence in salt rock mass is a reason for serious problems with shaft lining stability. Numerous trials have been done to provide appropriate shaft lining for salt layers, especially to ensure proper geometry of shaft members and conveyance guidance. In the new shaft lining concept, the excessive rock creep into the outbreak inside the shaft diameter is removed by local and controlled leaching of the shaft cheeks by means of fresh water through a porous medium at the contact layer behind the watertight tubing lining. The article presents the methodology of performing tests on a special device and the test results. Full article

(This article belongs to the Special Issue Geomechanics for Energy)

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