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1.
Deformation and stability of an elasto-plastic softening pillar 总被引：6，自引：0，他引：6
Summary A model of rock pillar or coal seam is considered assuming linear elastic behaviour before reaching the maximum strength and post-peak behaviour characterized by the residual strength. The deformation and stress across the pillar height are assumed to be uniform and the interaction with overlying rock strata is treated assuming beam model of the strata. The elasto-plastic stress distribution within pillar and the onset of instability occurring for the critical opening span are determined. Comparison with a solution for a simplified spring model of pillar is also presented. 相似文献
2.
V. Palchik 《Geotechnical and Geological Engineering》2000,18(1):39-51
Composite statistical analysis of the lithological composition of the rock mass above underground workings in coal seams and experimental work (laboratory mechanical tests and boring for the determination of hollows) in Donetsk city (Ukraine) have been used to develop a method for predicting the presence of hollows. The empirical criteria K1–K2>0 and K32.5 which relate to the physical characteristics of the overlying strata were found to predict the existence of such hollows in abandoned underground workings at shallow depth. The values of K1–K2 and K3 depend on the thicknesses of the different rock layers and the uniaxial compressive strength of the immediate roof over underground openings. The different layers e.g. sandstones, argillites, aleurolites and alluvium in the rock mass are shown to influence the existence of hollows in abandoned workings. Large thicknesses of sandstones in the rock mass or relatively high uniaxial compressive strength rock in the immediate roof contribute to the existence of hollows in abandoned workings. On the other hand, sandstones of small thickness, weak alluvium, argillites and aleurolites only give additional weight on immediate roof of the opening and allow collapse of the rock mass. The method of prediction for hollows was developed from the back-analysis of data from 41 boreholes which were drilled from the ground surface above underground openings. 相似文献
3.
The evaluation of the bearing strength characteristics of floor strata during an excavation process while under heavy loads from an overlying rock mass is one of the important factors in strata control of any underground mine. Plate loading tests on simulated floor strata were carried out for varying geotechnical conditions of weak floor strata. The physico-mechanical properties of weak floor strata evaluated in the experiments include unconfined compressive strength (c), elastic modulus (E), Poissons ratio () angle of friction (), and the moisture content (MC). The paper summarizes the results of (1) bearing strength tests using different sizes of circular loading plate (2) influence of various physico-mechanical parameters of weak floor strata on its floor bearing strength and (3) bearing strength analysis of weak floor in jointed rock mass. The outcome of the results show that the ultimate bearing strength decreases considerably with increase of footing plate size. The experimental results strongly support the earlier field investigation findings depicted by Zhanjing et al. (1992). Thus the contradictions about the plate size effect on bearing strength (Katsutoshi et al., 1998) are further eliminated. It was further investigated that apart from the plate size, ultimate bearing strength is strongly correlated with uniaxial compressive strength. A better correlation between moisture content and ultimate bearing strength with a regression coef.cient of 0.91 was also achieved. An excellent correlation between angle of friction () and ultimate bearing strength was found. 相似文献
4.
Summary The influence of rock discontinuities on mining-induced subsidence is addressed in this paper. A two-dimensional rigid block computer model was used to simulate discontinuities within strata overlying a longwall coal mine. Input for the model was available from a previous field study and numerical experiments were performed by varying the simulated joint stiffness, joint roughness, and vertical joint density. A comparison of simulated and measured displacements both within the overburden and on the surface provides insight into the influence of rock discontinuities. For the case in which all contacts had a relatively low stiffness, the maximum simulated subsidence was 293 mm whereas the case involving variable, but higher contact stiffness produced a maximum subsidence of only 73 mm reflecting the influence of increased overall stiffness. By comparison, the maximum measured subsidence was 580 mm. Consequently, the model behaved more stiffly than the actual rock mass but still provided a reliable simulation of block caving and strata separation. A comparison of simulated and observed displacements within the overburden suggests that horizontal discontinuities not included in the rigid block mesh above the zone of caving controlled rock mass compliance.List of Symbols
c
joint stiffness ratio [dimensionless]
-
d
strata thickness ratio [dimensionless]
-
e
strata modulus ratio [dimensionless]
-
E
a
modulus of stratum a [MPa]
-
E
b
modulus of stratum b [MPa]
-
E
equiv
equivalent rock mass modulus [MPa]
-
E
u
unconfined compression modulus of intact rock [MPa]
-
F
n
contact normal force [N]
-
h
overburden thickness [m]
-
k
a
normal spring stiffness of stratum a [N/m]
-
k
b
normal spring stiffness of stratum b [N/m]
-
k
equiv
equivalent rock mass spring stiffness [N/m]
-
K
n
normal material stiffness of joint [MPa/m]
-
K
s
shear material stiffness of joint [MPa/m]
-
m
mined thickness of coal seam [m]
-
q
u
unconfined compressive strength of intact rock [MPa]
- Sh
shale
- Ss
sandstone
- Sh/Ss
shale/sandstone interbeds
-
S
max
maximum subsidence [m]
- SLEX
Slope Indicator inclinometer/Sondex extensometer
-
T
a
thickness of stratum a [m]
-
T
b
thickness of stratum b [m]
-
T
j
joint thickness [m]
-
u
a
compression of stratum a [m]
-
u
b
compression of stratum b [m]
-
u
j
compression of joint [m]
-
u
total
total compression of strata and included joint [m]
-
w
width of longwall panel [m]
-
n
normal stress [MPa] 相似文献
5.
This paper presents an analytical model of a floor failure at a longwall coal mining face based on the multiple sliding block model. During longwall mining, stresses and displacements of strata are constantly changing. High stress concentrations at the coal face can exceed the rock strength and initiate fractures in the strata that can, under unfavourable conditions, lead to large floor displacements and disruption of mining operations. Underground observations of the rock floor and the computational modelling of the longwall face indicate that two types of fracture dominate floor failure. Extensive lateral fracturing often develops along the numerous weak bedding planes that are typically present in the sedimentary strata while sub-vertical fractures form in response to changing stress abutments ahead of the longwall coal face. The fractures that initially develop ahead of the longwall face are subject to a secondary movement when exposed ahead of the longwall supports. In response to the stress relief as the coal is mined from above, strata move towards the opening and bending of the floor occurs. If fractures in the floor exist, the floor blocks will displace in response to the floor movement and interact at the fractured surfaces. This analysis attempts to explain how the stress distribution develops within the broken floor during an active movement of floor strata leading to high stress concentrations at the floor level. The analytical formulation in this paper is supplemented by numerical modelling, and results are presented to verify that the analytical solutions are in accordance with the numerical predictions. 相似文献
6.
Arka Jyoti Das Prabhat Kumar Mandal Satya Prakash Sahu Angad Kushwaha Rana Bhattacharjee Subhashish Tewari 《Journal of the Geological Society of India》2018,92(6):732-742
The rock mass around an excavation is generally traversed by different geological discontinuities such as faults, folds, slips, joints, etc. Fault is one of the major geological discontinuities which creates lot of difficulties during underground winning of coal. Entire stress regime and ground conditions in the formation are altered in and around the faults. Faults also impose detrimental effects by introducing impurities, including clay and various forms of mineral matter into the coal seams; opening of pathways for the influx of water and gas into the underground workings; displacing the coal seams upward/downwards making the coal seams difficult or sometimes impractical to mine. Appropriate evaluation of the effect of the fault on the stability of the underground workings is a requisite for safe design of the underground mining structures. In this paper, a study has been carried out to assess the effect of the fault on the stability of underground coal mines by numerical simulation with distinct element method (DEM). On the calibrated DEM model, parametric study has been performed by varying the selected parameters, the dip and the friction angles of the fault. The analysis of variance (ANOVA) shows that both the factors have statistically significant effect on the strength of the coal pillar. Similarly, the displacement of the immediate roof and the height of the disturbed strata are evaluated by the DEM modelling and statistical analysis when the fault passes through the middle of the gallery. The results of ANOVA for both cases indicate that the both factors have significant effect on the displacement of the immediate roof and the height of the disturbed strata. It is obtained from the study that the low angle fault causes high instability in the immediate roof. The paper has been supplemented with the field observations where instability in underground roadways of a coal mine in India is caused by the fault. It was observed in VK-7 incline mine of Singareni Collieries Company Limited, India that there was sudden failure of immediate roof of a roadway where a low angle fault crosses the middle of the roadway. The findings of the paper help to understand the behaviour of the coal pillar and the surrounding rock mass in the presence of the fault. The study would also help to take appropriate decisions about the unstable regions of the working safeguarding safety in underground coal mines. 相似文献
7.
Joachim Jarke 《International Journal of Earth Sciences》1958,47(1):234-249
Zusammenfassung Der Begriff der Grenzschwellen ozeanischer Räume wird definiert und zunächst ihre Bedeutung für die Ausbildung der Beckenfazies dargelegt. Anschließend wird an Hand eines Schnittes über die Färöer-Island-Schwelle gezeigt, daß unter bestimmten hydrographischen Bedingungen auch die Faziesverhältnisse in Schwellenbereichen durch den durch die Dichteunterschiede bedingten Wasseraustausch zwischen zwei ozeanischen Räumen nachhaltig beeinflußt werden können. Es ergibt sich, daß sogar in Wassertiefen von 2000 m und mehr — lediglich als Folge von Überströmungsvorgängen — die Möglichkeit zur Bildung von sandigen Ablagerungen gegeben ist. Nicht jeder Sand des tiefen Wassers braucht demnach durch turbidity currents zu seinem Absatzort verfrachtet zu sein.Der mikrofaunistische Inhalt der Sedimente wird angegeben und in Verbindung mit den hydrographischen Verhältnissen — insbesondere den Temperatur-schwankungen im Grenzbereich zwischen dem kalten subarktischen und dem warmen nordatlantischen Wasser — betrachtet. 相似文献
8.
Summary This paper presents field observations on distribution of vertical stress during an experimental trial of extraction of pillars in four panels in 6.0–8.0m thick coal seam, as a part of a Science and Technology project funded by the Ministry of Coal, Govt of India. Variation of induced stress based on continuous monitoring data for the first time in Indian coal mining scenario showed distinct anomalies and potential for better understanding of strata mechanics and warning of major roof falls during pillar extraction. Numerical model studies based on finite difference code – FLAC were also conducted for stress analysis in idealized pillar mining sequence so that the influence of each stage of extraction could be identified. The numerical model results on stress concentration over the pillars, stooks and ribs showed variation of 3.6%, 8.3% and 6.1%, respectively as compared to the field observations for 7m thick coal seam at a depth cover of 60m from the surface. This indicates validity of the numerical models for stress analysis in the simulated conditions of the present field experiments. 相似文献
9.
针对煤矿井下水平井钻探中顶底板界面探测精度差、效率低等问题,进行煤矿井下防爆型随钻方位电磁波测井仪方案设计。为适合井下煤层工作环境,通过正演模拟获得源距、发射频率、线圈安装角度等仪器参数对信号响应影响的变化规律。研究结果表明:随钻方位电磁波仪器接收信号强度随发射频率、线圈距、地层电阻率对比度的增大而增强;线圈安装倾角约为45°时,既满足接收信号灵敏性,也满足信号的强度;仪器最佳工作频段为100 kHz~1 MHz。通过随钻方位电磁波测井仪响应模拟研究,为适用于煤矿井下仪器的参数优化设计提供选择依据,掌握了煤岩顶底板界面响应变化规律,该仪器的应用将提高顶底板探测精度和探测效率。 相似文献
10.
Multiple Failure State and Strain Controlled Triaxial tests 总被引：1，自引：0，他引：1
SummaryMultiple Failure State and Strain Controlled Triaxial Tests In this paper new methods are reported for the determination of the triaxial compressive strength of rocks. The Multiple Failure State Test with several single failure states in the same specimen, represents an extension of the classical testing procedure. The Strain Controlled Test is based, however, on a new concept and permits the determination of the failure envelope for a single test specimen. This type of test yields in addition useful information concerning the influence of changing lateral pressures and the influence of plastic deformations on the ultimate strength. A large number of tests with the different experimental methods and on several types of rock show good agreement in the results for the peak strength of intact rock as well as for the residual strength in the broken condition.
Study supported by the Swiss National Foundation for Scientific Research.
With 15 Figures 相似文献
ZusammenfassungTriaxialversuche mit mehrfachen Bruchzuständen und Versuche mit gesteuerter Dehnung Es wird über eine neue Methode zur Ermittlung der triaxialen Druckfestigkeit der Gesteine berichtet. Die Versuche mit mehrfachen Bruchzuständen am gleichen Prüfkörper stellen eine Erweiterung der klassischen Versuchstechnik dar. Die Dehnungsgesteuerten Triaxialversuche gehen jedoch von einem neuen Konzept aus und erlauben die Bestimmung der Mohrschen Umhüllenden am gleichen Prüfkörper. Diese Versuche vermitteln außerdem wertvolle Hinweise über den Einfluß veränderlicher Seitendrücke bzw. über den Einfluß der plastischen Deformationen im Bruchprozeß. Eine größere Anzahl von Versuchen mit den verschiedenen Methoden an mehreren Gesteinsarten zeigen übereinstimmende Resultate für die Höchstfestigkeit des intakten Gesteines als auch für die Restfestigkeit im gebrochenen Zustand.
RésuméEssais triaxiaux avec états de rupture multiples et essais avec déformation imposée Cet article décrit de nouvelles méthodes pour la détermination de la résistance des roches à la compression triaxiale. Les essais avec plusieurs états de rupture pour une même épouvette représentent une extension de la technique expérimentale classique. Les essais triaxiaux avec déformation imposée, par contre, sont d'une autre nature et permettent la détermination de l'enveloppe de Mohr avec une même éprouvette. De plus, les essais nous fournissent de précieuses indications sur l'influence de pressions latérales variables, resp. sur l'influence des déformations plastiques lors du processus de rupture. Le grand nombre d'essais effectués selon les différentes méthodes sur plusieurs types de roches montrent que les résultats concordent aussi bien pour la résistance maximale de la roche intacte que pour la résistance résiduelle de la roche fracturée.
Study supported by the Swiss National Foundation for Scientific Research.
With 15 Figures 相似文献
11.
Jane A. Gilotti 《Contributions to Mineralogy and Petrology》1989,101(1):30-45
The mylonite zone at the base of the Särv thrust sheet, Swedish Caledonides, contains diabase dikes which record intense deformation and syntectonic greenschist facies metamorphism. An angular shear strain of 100 is calculated for a single dike which can be followed for 50 m in the mylonite zone and abundant centimeter thick greenschist layers imply shear strains in excess of 1000. This extraordinary amount of deformation is comparable to the largest strains attained during experimental superplastic deformation of metals and alloys and, by analogy, suggests that dike deformation was macroscopically superplastic. The progress of five syntectonic reactions was measured as a function of increasing strain for the continuously exposed dike in order to assess the contribution of reactionenhanced ductility and fluid-rock interactions to strain localization along the thrust. Reaction progress calculations suggest that the breakdown of amphibole to form weaker phyllosilicates (which are added to the incompetent matrix fraction) is the important strain softening mechanism below 100. The ultimate tectonite is a stable biotite-epidote schist comprised of a uniformly fine grain size (< 200 m), constant grain shapes and strain free grains. Below 40, metamorphism was isochemical and shear strain was independent of H2O in the reactions. Petrologic fluid:rock ratios are low and suggest that deformation could have occurred under relatively dry conditions.Deformation micromechanisms were probably dominated by diffusive mass transfer processes throughout the life of the shear zone. The absence of cataclasis and the fine grain size of the protolith basalt suggest that fluids were introduced via grain boundary diffusion. Incongruent pressure solution at low strains and K-metasomatism above 40 also support diffusional flow. Diffusion-accomodated grain boundary sliding is thought to be the dominant micromechanism once the stable biotite-epidote tectonite forms. 相似文献
12.
The genesis of local compact segregations of iron sulfide (pyrite) in mudstones at the roof of some coal seams in the Donets Basin (Donbas) is examined. Arguments presented in the work show that sulfides were formed as a result of bacterial sulfate reduction and hydrogen sulfide generation in zones of organic matter concentration. The lack of any signs of influx of alien components testifies to in situ sulfide accumulations at the syngenetic or early diagenetic stage in bottom sediments of the basin. The shape and structure of pyrite segregations suggest that they could be sulfide bioherms occasionally subjected to mechanical deformation in a liquid mud under the influence of gravitational force or external mechanical (possibly seismic) loads. The obtained data can serve as an additional source of information pertaining to the formation conditions of sulfide ore deposits. 相似文献
13.
Ewa GłOwacka 《Natural Hazards》1993,7(2):121-132
Stress concentrations produced by rock deformation due to extraction in underground mines induce seismicity that can take the shape of violent and quite dangerous rockbursts.The hazard evaluation presented in this paper is based on a Bayesian probabilistic synthesis of information determined from mining situations during excavation, with previous and present data from microseismicity and seismoacustics.The method proposed in this study is an example of time-dependent on-line seismic hazard evaluation. All results presented were obtained retrospectiely for different underground coal mines in Poland and Czechoslovakia.On leave from Institute of Geophysics, Polish Academy of Sciences 01-452 Warszawa, ul. Ksiecia Janusza 64, Poland. 相似文献
14.
E. Althaus A. Friz-Töpfer Dr. rer. nat. Ch. Lempp O. Natau 《Rock Mechanics and Rock Engineering》1994,27(1):1-21
Summary Deformation experiments have been performed in a triaxial compression cell at a temperature of 300°C and confining pressures up to 65 MPa using samples of homogeneous, fresh two-mica-granite (RM) and monzogranite (CM). The cylindrical specimens (d=70 mm, h=140 mm, V=540 cm3) were tested undrained under dry (105°C), as received, and water saturated conditions at deformation rates between
and
. The mechanical behaviour of the two types of coarse-grained, crystalloblastic granites is critically influenced by mineralogical composition, porosity, and the amount of intergranular water present in the samples. The failure stress of the CM granite is at about 65% of that of the RM granite; in both rocks strength decreases with increasing porosity and water content.The presence of interstitial water causes a failure mode of non-localized, homogeneously distributed microcracking in the central parts of the samples, whereas, in runs with dry granites, strain localization along a single shear fracture was observed. When aqueous fluids are present, the macroscopic style of deformation of granites appears to be ductile even at lowP andT conditions. Strength and angle of internal friction are reduced to very low values. The style of deformation, as well as the reduction of strength of the water-saturated rock samples, is due to mechanical and chemical effects of intergranular water at elevated temperatures.The maximum differential stresses measured for these coarse-grained granites are much lower than the strength commonly reported for other granites, e. g. Westerly and Charcoal granites. Our data suggest that the strength of the granitic crust under differential stress is lower than currently deduced from laboratory experiments. 相似文献
15.
The introduction of roofbolting in the UK coal mining industry has been well documented and is an example of reinforcement design utilizing a design by measurement or observational approach. This has involved detailed monitoring of rock strata movements and rockbolt loads at a large number of sites. Analysis of roadway deformation monitoring information from across the Selby coalfield provided an ideal opportunity of assessing how geological and stress variations affect the stability of reinforced coal mine roadways. Statistical analysis of this data has confirmed the detrimental effects of maximum horizontal stress direction and relatively weak roof geology on the magnitude of roof deformation. Further analysis has led to the development of a roof lithology index for assessing the quality of the immediate roof geology and the use of geological hazard analysis for providing useful information for the development of a stability index for assessing support requirements of existing and future roadways. This investigation has also verified previous observations regarding mechanisms controlling roadway deformational behaviour and highlights the importance of the site-specific nature of reinforcement design. 相似文献
16.
The shear strength of rock joints in theory and practice 总被引：62，自引：10，他引：62
SummaryThe Shear Strength of Rock Joints in Theory and Practice The paper describes an empirical law of friction for rock joints which can be used both for extrapolating and predicting shear strength data. The equation is based on three index parameters; the joint roughness coefficientJRC, the joint wall compressive strengthJCS, and the residual friction angle
r
. All these index values can be measured in the laboratory. They can also be measured in the field. Index tests and subsequent shear box tests on more than 100 joint samples have demonstrated that
r
can be estimated to within ± 1° for any one of the eight rock types investigated. The mean value of the peak shear strength angle (arctan/
n
) for the same 100 joints was estimated to within 1/2°. The exceptionally close prediction of peak strength is made possible by performing self-weight (low stress) sliding tests on blocks with throughgoing joints. The total friction angle (arctan/
n
) at which sliding occurs provides an estimate of the joint roughness coefficientJRC. The latter is constant over a range of effective normal stress of at least four orders of magnitude. However, it is found that bothJRC andJCS reduce with increasing joint length. Increasing the length of joint therefore reduces not only the peak shear strength, but also the peak dilation angle and the peak shear stiffness. These important scale effects can be predicted at a fraction of the cost of performing large scale in situ direct shear tests.With 20 Figures 相似文献
17.
A 3D model of a jointed rock mass and its deformation properties 总被引：1，自引：0，他引：1
Faquan Wu 《Geotechnical and Geological Engineering》1988,6(2):169-176
Conclusion A geometric model of a jointed rock mass and some formulae of strain and deformation parametersE, G and were given. They may be useful for evaluating the deformation parameters of rock masses and classifying the rock mass quatitatively. 相似文献
18.
The transformation from blueschist to greenschist facies forms a major part of the Alpine regional geodynamic evolution of the Cyclades. The transition in metabasic rocks on Sifnos involves the retrogression of eclogites, blueschists and actinolite-bearing rocks from high-pressure conditions which have been estimated at 460±30° C and 15±3 kb. Petrographically observed parageneses are interpreted by a sequence of hydration and carbonation reactions involving the breakdown of omphacite and glaucophane-bearing assemblages to albite+chlorite±actinolite±calcite assemblages. The retrograde processes are calculated to occur at pressures of 10 to 8 kb during the isothermal uplift of the Sifnos units. Oxygen isotope analyses of different rock types show that interlayered lithologies have experienced a large degree of isotopic equilibration during both metamorphic phases. However, chemically equivalent rocks show systematic increases in
18O from lowest values (8 to 11 in metabasics) in the unaltered blueschists in the upper stratigraphic levels to higher values (>15 in metabasics) associated with greenschists in the deepest stratigraphic levels. Relict eclogites enclosed within greenschists have the lower
18O values typical of unaltered blueschist facies rocks. These isotopic gradients and the
13C and
18O compositions of carbonates demonstrate an infiltration mechanism involving the upward movement of 18O-enriched fluids whose compositions were buffered by exchange with marble units. Calculated minimum fluid/rock ratios for the blueschist-to-greenschist transition decrease from 0.4 in the deepest studied level (Central Sifnos) and 0.2 in the intermediate level (Kamares Bay samples) to an assumed value of zero in unaltered blueschists. These ratios may be lower if recycling of fluids occurred between schists and marbles. Infiltration of fluids became inhibited as the transformation advanced as a consequence of sealing effect of the hydration and carbonation reactions. Although infiltration most probably was a pre-requisite for the regional occurrence of the blueschist-to-greenschist transformation in the Cyclades, the evidence on Sifnos does not suggest the introduction of large quantities of fluid. 相似文献
19.
Manuel Rocha Medal Recipient Rock Fracture and Collapse Under Low Confinement Conditions 总被引：6，自引：4，他引：2
M. S. Diederichs 《Rock Mechanics and Rock Engineering》2003,36(5):339-381
Summary The primary objective of this work was an examination of the complimentary roles of tensile damage and confinement reduction (or stress relaxation) on excavation response of hard rockmasses. Tensile damage and relaxation are examined with respect to structurally controlled or gravity driven failure modes as well as to strength controlled or stress driven rockmass damage and yield. In conventional analysis of both structurally controlled and stress driven failure, the effects of tensile damage and tensile resistance as well as the elevated sensitivity to low confinement are typically neglected, leading to erroneous predictions of groundfall potential or rock yield. The important role of these two elements in underground excavation stability in hard rock environments is examined in detail through a review of testing data, case study examination and a number of analytical and numerical analogues including discrete element simulation, statistical theory and fracture mechanics. This rigorous theoretical treatment updates, validates and constrains the current use of semi-empirical design guidelines based on these mechanisms. 相似文献
20.
不同岩性顶板回采工作面矿压分布规律 总被引：4，自引：0，他引：4
采用数值模拟技术和现场矿压观测系统,研究了不同岩性顶板回采工作面矿压分布规律及其显现特征。结果表明,在煤炭开采过程中,不同岩性顶板回采工作面最大支承应力存在一定差异,在强度较高的砂岩顶板岩体中,支承压力大,工作面前方支承压力峰值距工作面距离小,初次来压步距和周期来压步距大,矿压显现强烈;而在强度较低的泥岩顶板区,顶板岩体不能和砂岩骨架层一样抵抗覆岩压力,且支承压力小,支承压力的峰值向回采工作面前方岩体内部推移,初次来压步距和周期来压步距小,矿压显现不明显。 相似文献