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The maximum diving depth of modern submarines has always been increasing. Although this has been useful and in some cases necessary, it usually comes with some risks. For instance, when a submarine encounters an emergency situation that requires immediate ascent from great depths, the situation becomes more dangerous, especially due to its rolling characteristics. To investigate the effect of unsteady forces during free ascent motion of submarines at great depths on submarine rolling, in this study, the SST-DDES model combined with the overset grid technique was used for the numerical simulation of a submarine free ascent. Water tank experiments for free ascent were conducted to validate the numerical approach, which confirmed the reliability of the numerical method. Following this, the CFD method was employed to conduct an initial exploratory investigation into the free ascent motion of deep-submergence submarines. The free ascent motion of submarines at great depths under five different degrees of freedom combinations was studied. The computational results indicated that submarines are more prone to roll over during free ascent at great depths. At a depth six times the length of the submarine, the maximum roll angle underwater reaches 22.8°. In addition, unsteady rolling moments, lateral forces, and yawing moments have a significant effect on submarine rolling, intensifying the tendency to roll. Furthermore, it was observed that the vertical hydrodynamic attack angle β is related to the rolling stability of the submarine, such that a moderate decrease in β is beneficial for the rolling stability. The numerical calculation method and preliminary research findings can provide theoretical support for controlling the ascent motion of real submarines. [ABSTRACT FROM AUTHOR]

The article addresses the problem on thermal stresses and stress–strain behavior of rock mass during deep-level mining. The author proposes an approach to determining the stationary field of temperatures in the zone of mining with cemented paste backfill with single formation of stiffness matrix in the calculation. It is found that inclusion of the temperature change depthward rock mass in the analysis results in the increase in the initial horizontal stresses while the initial vertical stresses remain unaltered. The calculation method of stress redistribution in the course of mining with backfill, with the same stiffness matrix used at all calculation stages, is modified for taking into account the thermal stresses. The calculation of the thermal stress state of surrounding rocks and backfill is carried out for a case of mining with backfill in a gently dipping ore body. [ABSTRACT FROM AUTHOR]

A variety of coal room and pillar mining methods have been efficiently practiced at depths of up to 500 m with least strata mechanics issues. However, for the first time, this method was trialled at depths of 850–900 m in CSM mine of Czech Republic. The rhomboid-shaped coal pillars with acute corners of 70°, surrounded with 5.2 m wide and 3.5–4.5 m high mine roadways, were used. Pillars were developed in a staggered manner with their size variation in the Panel II from 83 m × 25 m to 24 m × 20 m (corner to corner) and Panel V from 35 m × 30 m to 26 m × 16 m. Coal seam inclined at 12° was affected by the unusual slippery slickenside roof bands and sometimes in the floor levels with high vertical stress below strong and massive sandstone roof. In order to ensure safety, pillars in both the panels were continuously monitored using various geotechnical instruments measuring the induced stresses, side spalling and roof sagging. Both panels suffered high amounts of mining induced stress and pillar failure with side-spalling up to 5 m from all sides. Heavy fracturing of coal pillar sides was controlled by fully encapsulated steel bolts. Mining induced stress kept increasing with the progress of development of pillars and galleries. Instruments installed in the pillar failed to monitor actual induced stress due to fracturing of coal mass around it which created an apprehension of pillar failure up to its core due to high vertical mining induced stress. This risk was reduced by carrying out scientific studies including the three-dimensional numerical models calibrated with data from the instrumented pillar. An attempt has been made to study the behavior of coal pillars and their yielding characteristics at deeper cover based on field and simulation results.

The maximum diving depth of modern submarines has always been increasing. Although this has been useful and in some cases necessary, it usually comes with some risks. For instance, when a submarine encounters an emergency situation that requires immediate ascent from great depths, the situation becomes more dangerous, especially due to its rolling characteristics. To investigate the effect of unsteady forces during free ascent motion of submarines at great depths on submarine rolling, in this study, the SST-DDES model combined with the overset grid technique was used for the numerical simulation of a submarine free ascent. Water tank experiments for free ascent were conducted to validate the numerical approach, which confirmed the reliability of the numerical method. Following this, the CFD method was employed to conduct an initial exploratory investigation into the free ascent motion of deep-submergence submarines. The free ascent motion of submarines at great depths under five different degrees of freedom combinations was studied. The computational results indicated that submarines are more prone to roll over during free ascent at great depths. At a depth six times the length of the submarine, the maximum roll angle underwater reaches 22.8°. In addition, unsteady rolling moments, lateral forces, and yawing moments have a significant effect on submarine rolling, intensifying the tendency to roll. Furthermore, it was observed that the vertical hydrodynamic attack angle β is related to the rolling stability of the submarine, such that a moderate decrease in β is beneficial for the rolling stability. The numerical calculation method and preliminary research findings can provide theoretical support for controlling the ascent motion of real submarines.

Back in the early 1980s, coal deposits occurring at depths of ~700 m below surface were already regarded as large-depth deposits. Meanwhile, today the borderline depth of large-depth mining has extended to >1,000 m. Design, excavation and maintenance of mining roadways at the depth of >1,000 m have, therefore, become crucial issues in a practical perspective in recent years. Hence, it is now extremely important to intensify research studies on the influence of large depths on the behaviour of rock mass and deformation of support in underground excavations. The paper presents the results of the study carried out in five mining excavations at depths ranging from 950 to 1,290 m, where monitoring stations with measurement equipment were built. The analysis of data from laboratory and coal mine tests, as well as in situ monitoring, helped to formulate a set of criteria for stability assessment of underground excavations situated at large depths. The proposed methodology of load and deformation prediction in support systems of the excavations unaffected by exploitation is based on the criteria referring to the depth of excavation and the quality of rock mass. The depth parameter is determined by checking whether the analysed excavation lies below the critical depth, whereas the rock mass quality is determined on the basis of the roof lithology index (WL) and the crack intensity factor (n)

This case study presents the verification of two surface subsidence prediction models for longwall mining at depths greater than 400 m. The surface subsidence points were surveyed and compared for both models. The first model uses empirical calculations to predict the surface subsidence. This method is reliable for predicting surface subsidence at shallower depths. At present, however, coal mining has progressed to great depths. The second model is the 2-dimensional finite element method to predict surface subsidence. In contrast to the first method, this method is based on the regional parameters and uses the rock mass properties to evaluate surface subsidence for multiseams at any depth. Results show that the finite element method gives a better approximation of the measured surface subsidence than the Knothe method. The maximum surface subsidence, which was determined by the FEM method, was used to adjust the extraction coefficient in the Knothe's method. The predicted value differs from the measured value by 8%. The slope of the predicted subsidence trough was within the range of 2'8% from the surveyed subsidence. This case study proposes a procedure for using both models to successfully predict the surface subsidence. [ABSTRACT FROM AUTHOR]

• Visco-elastic solutions for tunnel excavation considering supporting delay are presented. • Three-dimensional effect of tunnel faces is considered. • The interaction between liner and geomaterial is considered. • Different visco-elastic models are applied to simulate geomaterial. This paper proposes complex variable solutions for stress and displacement fields for tunnel excavation at great depth in a visco-elastic geomaterial, considering the equivalent three-dimensional effect, liner installation, supporting delay, and the interaction between liner and geomaterial. The geomaterial is simulated by three typical visco-elastic models: the three-parameter solid model, the Poyting–Thomson model and the Burgers model. The proposed solutions can simulate both tunnel excavation and liner installation stages, which are continuous in the time dimension. In the derivation, the variable substitution, the Laplace transform, and their inverse computations are applied. The proposed solutions are verified in detail by comparing to a numerical solution and a set of field data. Good agreements between the analytical solution and the numerical solution/field data are observed, indicating the validity of the proposed solutions. Subsequently, a parametric study is performed to investigate the influences of tunnel geometry (including tunnel size and liner thickness), material parameters of liner and geomaterial (including Poisson's ratio, shear modulus and viscosity of both elements), tunnel advance rate, and liner installation time moment (denoting supporting delay) on the stress and displacement fields in liner and geomaterial. The proposed solutions may serve as an alternative method for the conceptual and preliminary designs in tunnel engineering. [ABSTRACT FROM AUTHOR]

• Analytical solutions for twin tunneling are presented. • Solutions are valid for (1) newly constructed twin tunneling; (2) single tunneling influencing an existing tunnel. • Solutions are valid for the whole twin tunneling process (4 stages). • Twin tunnels with arbitrary geometry and arbitrary liner properties are considered. Analytic solutions for stress and displacement of twin tunneling at great depth considering liner installation and mutual interaction between geomaterial and liners are the key context in this paper. Twin tunneling is a continuous procedure, in which after one tunnel is excavated and lined, the other one is hysteretically excavated and lined. The presented solutions mainly focus on stress and displacement in geomaterial and liners for the hysteretical phases through an iterative combination of the complex variable method and the Fourier transform via the Schwarz alternating method. The presented solutions are verified by comparing to a corresponding numerical solution of a general case, in which a good agreement is observed after three iterations. Subsequently, a dimensionless parametric investigation is performed to investigate the influence of tunnel geometry (including twin tunnel spacing, relative angle of twin tunnels and relative size of twin tunnels), liner properties (including liner thickness and liner installation), and lateral stress coefficient on stress and displacement in both liners and geomaterial. [ABSTRACT FROM AUTHOR]

Problematics. Due to the ambiguous understanding of the nature and void space distribution within reservoir rocks, prediction of prospective deep buried and low permeable reservoirs becomes more uncertain. There are many factors influencing on the pore space, such as primary rock composition, hydrogeological regime, tectonic processes, geological time, epigenetic processes etc. Moreover, in explanation of different factors the influence of secondary reservoirs formation, systematization problems become more essential. Either, it is important to identify ‘working’ conditions of influencing factors to make the prediction of hydrocarbon deposits at great depth more certain. Finding universal criteria of prospective secondary reservoir rocks identification will allow us to enhance the discovery rate of deep buried hydrocarbon deposits. Analysis of previous studies. Many researches were devoted to epigenetic processes in the second part of XXth century. There were described major secondary alterations which may occur at great depth. Recent publications showed the expansion of previous knowledge about epigenetic processes and their influence on the secondary deep buried reservoir formation. Some scientists state that major influencing factors on reservoir quality are tectonic and primary mineral composition, others bring epigenetic imposed processes to the top of influencing factors. Purpose. The purpose of the research is to study secondary alterations and find possible zonation based on the alteration intensity of Carboniferous (Viséan and Serpukhovian) rocks within Central part of the Dnieper-Donets basin. Methods. During this research we studied 43 thin sections of Carboniferous sandstones from cores of Central part of the Dnieper-Donets basin, using polarizing microscope. Alteration stage analyses were used for determination of mineral sequence transformations. Results. Carboniferous (Viséan and Serpukhovian) sandstones discovered by deep wells within Solokhivsko- Dykanskyi and Berezivsko-Kotelevskyi archs in Central part of the Dnieper-Donets depression have been studied. Microscopic studies have shown widespread development of imposed epigenetic alterations in terrigenous rocks. The involvement of laboratory evaluation of porosity and permeability, as well as the values of formation temperatures, allowed us to determine the main trends of secondary processes effect on reservoir properties of rocks. It is shown that the development of secondary microfracturing, kaolinitization and sideritization increases the value of porosity and permeability. Dissolution, regeneration and redeposition of quartz are accompanied by calcitization and lead to the significant decrease of the reservoir properties of terrigenous rocks and formation of secondary epigenetic seals. Sideritization facilitates the development of secondary reservoirs at great depth, meanwhile calcitization leads to decrease of the pore space. Bitumoids and pyrite presence may be the evidence of hydrocarbon migration process. Combination of the research results with thermobaric data retrieved directly from borehole measurements as well as theoretically calculated on Bilske gas condensate field shows that formation of epigenetic seal in the temperature interval of 110-120 °C is caused by quartz dissolution and intensive calcitization of terrigenous rocks. Consequently, secondary reservoir rocks below the epigenetic seal have local spreading caused by microfracturing, sideritization and calcitization. Specific secondary sandy reservoirs of Berezivske gas condensate field are located within 110 and 120 °C isotherm. They occurred in acid environment leading to dissolution of calcite cement and intense sandstone kaolinitization. Such favorable conditions for secondary porosity formation may occur as a result of possible tectonic movements inversion which triggered the development of regressive epigenesis. [ABSTRACT FROM AUTHOR]

Gestosc objetosciowa skał oraz predkosc fal sprezystych sa stosowane do identyfikacji własciwosci i litologii skał na duzych, niedostepnych dla bezposrednich obserwacji głebokosciach. Znaczne cisnienie (P) oraz wysoka temperatury (T) powoduja zmiany predkosci propagacji fali (Vp) oraz gestosci objetosciowej (ρs), co utrudnia zdalne rozpoznanie odmiennych litologicznie skał oraz prowadzi do znacznych błedów w ocenie inzynierskiej ich parametrów.

The 'Deep geothermal power station' project represents a new process for the exploitation of geothermal energy. District heating and heating for industrial purposes as well as electricity can be produced in a geothermal power station. The heat extraction will be controlled and continuous in a closed circulation system using drillings from a mined system of tunnels at a depth of 6,000 m. In order to overcome the high temperatures and rock pressures to be expected, interdisciplinary collaboration between several professions will be required. Das Projekt 'Geothermietiefenkraftwerk' stellt einen neuen Verfahrensansatz in der Nutzung geothermischer Energie dar. Fernund Prozesswärme sowie Elektrizität werden hierbei in einem geothermischen Großkraftwerk erschlossen. Die Wärmegewinnung erfolgt kontrolliert und kontinuierlich in einem geschlossenen Kreislauf mittels Bohrungen von einem bergmännisch aufgefahrenen Stollensystem in einer Teufe von 6.000 m. Zur Beherrschung der hohen Temperaturen und Gebirgsdrücke ist eine interdisziplinäre Zusammenarbeit mehrerer Fachdisziplinen erforderlich. [ABSTRACT FROM AUTHOR]

Abstract: In order to examine whether the anelastic strain recovery (ASR) method can be applied for determining the in situ stress in hard rocks at great depths, the anelastic strain recovery of oriented cores was measured in six independent directions. The core specimens were taken from four depths within the range of about 2400–4500 m MD at the METI Niitsu well in Japan; the rock materials were mudstone, dolerite, basalt and andesite. For all the rocks the expansional anelastic strains were obtained, the magnitude of the strains in various directions continuously measured for 1 or 2 weeks was of the order of 1000×10−6 in mudstone; in contrast, strains of the other cores did not exceed a few hundred microstrains. These strains were used for a three-dimensional analysis of the principal in situ stresses. At the third depth, the principal stress directions were considered to be affected by fractures pre-existing near the core, and showed the features of a very local stress state. With the exception of this data, the directions determined by the ASR method were in agreement with those determined using other in situ measurement methods. Based on two assumptions, i.e., (i) the rock stress in vertical direction is equal to density-related gravitational overburden stress, (ii) the ratio of anelastic strain recovery compliance of shear deformation mode and the compliance of volumetric deformation mode is equal to 2, the values of the three principal stresses were estimated. The values of the minimum principal stress in the plane perpendicular to the well axis determined in this study were in agreement with those determined based on extended leak-off tests (ELOT or XLOT) conducted at the same well. Therefore, it can be said that the ASR method is well suited for use in directly determining the directions of principal in situ stresses in three dimensions and in estimating the magnitude of the stresses in isotropic rocks at great depths, such as those encountered when drilling deep into a submarine seismogenic zone. [Copyright &y& Elsevier]

Pleistocene sediments deposited in Osaka Bay have been extensively investigated to depths of up to 400 m. Consolidation properties, especially preconsolidation pressure, are somewhat scattered with depth. The quality of samples retrieved from great depths has been evaluated based on the indices calculated from the volumetric strain or the void ratio changes in the recompression process. The study reveals that these indices do not simply increase with an increase in sampling depth. The potential for sample disturbance during sample setting in the constant rate of strain (CRS) oedometer was also investigated. These tests have revealed that the preconsolidation pressure, as measured in the laboratory, is not influenced significantly by swelling. In addition, preconsolidation pressures indicate that the sediments are slightly overconsolidated, with a departure from normally consolidated behaviour that could be explained by cementation.Key words: sampling, preconsolidation pressure, sample disturbance, oedometer test, Pleistocene clay, great depth.Les sédiments du pléistocène déposés dans la Baie d'Osaka ont fait l'objet d'études élaborées jusqu'à des profondeurs de 400 m. Les propriétés de consolidation, particulièrement la pression de préconsolidation, sont quelque peu dispersées en fonction de la profondeur. La qualité des échantillons prélevés à de grandes profondeurs a été évaluée sur la base des indices calculés en partant de la déformation volumétrique ou des changements d'indice de vide durant le processus de recompression. L'étude révèle que ces indices ne croissent pas simplement avec l'augmentation de la profondeur d'échantillonnage. L'étude considère aussi le potentiel du remaniement de l'échantillon durant sa mise en place dans l'oedomètre à taux constant de déformation (CRS). Ces essais ont révélé que la pression de préconsolidation telle que mesurée en laboratoire n'est pas influencée de façon significative par le gonflement. De plus, les valeurs de la pression de préconsolidation indiquent que les sédiments sont légèrement surconsolidés, avec un écart par rapport au comportement normalement consolidé qui pourrait être expliqué par la cimentation.Mots clés : échantillonnage, pression de préconsolidation, remaniement d'échantillon, essai oedométrique, argile du pléistocène, grande profondeur.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Runup on a slender cylindrical column exposed to long, steep waves, at finite and great depth is quantified by high speed camera technique in wave channel. Ratio between water depth (h) and cylinder diameter (D) is h / D = 10,4.16 , 2. 5. Breaking and non-breaking wave events are made by focusing technique. The trough-to-trough period (T T T ), crest height (η 0. m ), frequency (ω = 2 π / T T T ) and reference speed (g / ω) of each wave event are defined (g denotes acceleration of gravity). Wavenumber (k) is obtained from the dispersion relation. Experimental runup maximum (R u m) is presented in terms of variable Z = [ 2 ω 2 (R u m − η 0 , m ) / g ] 1 / 2 . Measurements at finite water depth collapse along a linear relationship k η 0 , m = a + b Z where coefficients are obtained from the experiments. Results from other studies including large scale measurements fit to this curve, for h / D < 5 , k h < 2 and k D < 0.52. Results at great water depth with h / D = 10 show, beyond a threshold wave slope, a similar relationship. Growth factor (1 / b) is then much stronger. Gradual transition between results at finite depth and great water depth occurs for 5 < h / D < 10 and k h > 2.5. Measured runup velocity along the column is up to 1.8 times the reference speed at great depth (h / D = 10) and up to 1.2 times the reference speed at finite depth. Wave slope k η 0 , m is up to 0.56. • Videoimages of wave runup on a column are digitized. • The runup is presented in nondimensional form. • There is collapse of the runup data at great depth and at finite depth. • Runup velocity relative to the wave propagation speed shows another collapse of the data. • Results are suitable for offshore windfarm developments. [ABSTRACT FROM AUTHOR]