Mining Sequence Deformation and Failure Behaviour Analysis in the hangingwall and Orebody Rock Formations; A Continuum Approach

In this study based on practical geological setting of the hangingwall, orebody and footwall. Two comprehensive evaluation models for selecting the underground mining method to extract the Nchanga Upper Orebody were proposed which constituted of six key attributes of technical economic, rock substance strength, production, orebody dip and thickness. These evaluation models are analyzed by the multiple attribute decision making methods based on eigenvalues, eigenvectors and fuzzy mathematics. In addition two different continuum numerical methods Examine^2D and RS³ are employed to simulate the mining process of the Upper Orebody and finally the optimal mining scheme is determined. By using analytical hierarchy process, Yager’s method and numerical modeling some useful conclusions for mining the highly folded Upper Orebody have been drawn, which will be beneficial to the Nchanga mine.     

Characteristics of Coal Ashes in Yanzhou Mining District and Distribution of Trace Elements in Them

In the process of combustion of coal organic and inorganic materials in it will undergo a complex variation.Part of thew will become volatiles and,together with coal smoke,enter into atmosphere,some will remain in micro-particulates such as ash and dust and find their way into atmosphere in the form of solid particles,and the rest will be retained in ash and slag.Coal ashes are the residues of organic and inorganic substances in coal left after coal combustion and the compostition of coal ashes in dependent on that of minerals and organic matter in coal.This paper deals with the chemical composition of coal ashes,the distribution of trace elements in them and their petrological characteristics,and also studies the relationship between the yield of coal ashes and the distribution of trace elements.In addition,a preliminary study in also undertaken on the factors that affect the chemical composition of coal ashes.As viewed from the analyses of coal ash samples collected from the Yanzhou mining district,it can be seen clearly that coal ashes from the region studied are composed chiefly of crystalline materials,glassy materials and uncombusted organic matter and the major chemical compositions are SiO2,Al2O3,Fe2O3,and CaO,as well as minor amounts of SO3,PWO5,Na2O,K2O and TiO2.During the combustion of coal,its trace elements will be redistributed and most of them are enriched in coal ashes.At the same time,the concentrations of the trace elements in flying ash are much higher than those of bottom ash,i.e.,with decreasing particle-size of coal ashes their concentrations will become higher and higher.So the contents of trace elements are negatively proportional to the particle-size of coal ashes.There has been found a positive correlation between the trace elements Th.V.Zn,Cu and Pb and the yield of coal ashes while a negative correlation between Cl and the yield of coal ashes.     

Comparison Between Stress and Strain Quantities of the Failure–Deformation Process of Fennoscandian Hard Rocks Using Geological Information

The aim of this paper was to compare the stress and strain quantities that are related to the failure–deformation process of hard rock. The data used here was obtained from laboratory uniaxial compression tests performed on different types of Fennoscandian hard rocks. The failure–deformation process quantities were compared at each deformation stage and for each single specimen. Moreover, geological information such as the rock origin process and the rock characteristics of the specimens were studied and linked to the stress and strain quantities. The purpose was to investigate the influence of the rock origin process and rock characteristics on these quantities. The main results of this study showed that the normalized crack damage lateral strain (ε _3cd/ε _3p ) and the volumetric strain (ε _crv?ci and ε _v?cd) quantities were strongly affected by the grain size. The normalized and volumetric quantities are weakly dependent on the mineral composition.     

Deformation and Compression Behaviour of a Cement–Bentonite Slurry for Groundwater Control Applications

Cement bentonite (CB) barriers are self-supporting, low permeability, structures used to retard groundwater flow and as such strength and hydraulic conductivity parameters are often stipulated when developing the mixtures. This paper reports an investigation into the deformation and compression behaviour of a CB containing ground granulated blastfurnace slag using the unconfined compressive strength apparatus, triaxial (undrained, unconsolidated) and oedometer. Samples were also exposed to drying and rewetting to investigate possible response to changes in environmental conditions. Cracking was observed prior to peak stress suggesting that the hydraulic conductivity of a barrier may be adversely affected before the shear strength is reached in undrained conditions. The compression response of CB indicates the presence of a threshold stress; once exceeded the magnitude of settlements are significantly greater than those encountered below this threshold. If a barrier experiences localised changes in loading conditions then there is the potential for damage from induced differential settlements; thus it is recommended that the threshold stress should also be considered at the design stage in addition to strength and hydraulic conductivity requirements. The response of the material exposed to drying-rewetting was unexpected and requires further investigation to determine how a barrier will respond to changing environmental conditions.     

Stress and Deformation Analysis of Concrete-Facing Sand–Gravel Dam Based on Inversion Parameters

With the long-term operation of the project, the material parameters of concrete-facing sand–gravel dam will change, which brings great difficulty to the scientific and effective stress and deformation analysis. Combining with the measured displacement data, the finite element analysis model of the concrete-facing sand–gravel dam of Heiquan reservoir was established, and the modulus of elasticity and internal friction angle of the dam body were inverted by the measured displacement of the dam, then the simulation analysis of the filling construction process and the reservoir storage process of dam was carried out, and the stress and deformation values of the dam during the construction period and the impoundment period were calculated. The results showed that the parameters obtained from the inversion are smaller than the original parameters, but there is little difference between them. The displacement calculated by finite element inversion was close to the measured displacement value, the overall displacement and stress distribution of the dam body and panel were in line with the general law, and the calculated displacement and stress values were at the normal level. This study provides a reference for parameter inversion and stress and deformation analysis of concrete slab dam through monitoring data analysis.

     

Evolutionary Stages of the Earliest Skeletal Fauna and Division and Correlation of the Precambrian-Cambrian Boundary Strata

Through an analysis of the earliest fossils in the Precambrian-Cambrian boundary beds in various parts ofthe world, especially in the Yangtze and Siberia platforms, the author has found that the evolution of the ea-rliest skeletal animals may be divided from older to younger into three stages. The first stage (theAnabarites-Protohertzina fauna) is represented by the Anabarites-Protohertzina zone of the Meishucunian Stagein the Yangtze platform and the A. trisulcatus and P. cristata zones of the Manykayn Stage in Siberia. The sec-ond stage (the earliest orthothecimorphid and mollusc fauna) is represented by the Paragloborilus-Siphogonuchites zone of the Meishucunian Stage and the Aldanocyathus sunnaginicus zone of the TommotianStage. The third stage (the earliest hyolithimorphid and lapworthellid fauna) is represented by the Sinosachiteszone of the Meishucunian Stage and the D.regularis and D.lenaicus zones of the Tommotian Stage. The threeevolutionary stages can be used as a criterion for worldwide correlation.     

Deformation,metamorphism, and mobilization of Ni–Cu–PGE sulfide ores at Garson Mine,Sudbury

The Garson Ni–Cu–platinum group element deposit is a deformed, overturned, low Ni tenor contact-type deposit along the contact between the Sudbury Igneous Complex (SIC) and stratigraphically underlying rocks of the Huronian Supergroup in the South Range of the 1.85-Ga Sudbury structure. The ore bodies are coincident with steeply south-dipping, north-over-south D₁ shear zones, which imbricated the SIC, its ore zones, and underlying Huronian rocks during mid-amphibolite facies metamorphism. The shear zones were reactivated as south-over-north, reverse shear zones during D₂ at mid-greenschist facies metamorphism. Syn-D₂ metamorphic titanite yields an age of 1,849?±?6 Ma, suggesting that D₁ and D₂ occurred immediately after crystallization of the SIC during the Penokean Orogeny. The ore bodies plunge steeply to the south parallel to colinear L₁ and L₂ mineral lineations, indicating that the geometry of the ore bodies are strongly controlled by D₁ and D₂. Sulfide mineralization consists of breccia ores, with minor disseminated sulfides hosted in norite, and syn-D₂ quartz–calcite–sulfide veins. Mobilization by ductile plastic flow was the dominant mechanism of sulfide/metal mobilization during D₁ and D₂, with additional minor hydrothermal mobilization of Cu, Fe, and Ni by hydrothermal fluids during D₂. Metamorphic pentlandite overgrows a S₁ ferrotschermakite foliation in D₁ deformed ore zones. Pentlandite was exsolved from recrystallized polygonal pyrrhotite grains after cessation of D₁, which resulted in randomly distributed large pentlandite grains and randomly oriented pentlandite loops along the grain boundaries of polygonal pyrrhotite within the breccia ore. It also overgrows a S₂ chlorite foliation in D₂ shear zones. Pyrrhotite recrystallized and was flattened during D₂ deformation of breccia ore along narrow shear zones. Exsolution of pentlandite loops along the grain boundaries of these flattened grains produced a pyrrhotite–pentlandite layering that is not observed in D₁ deformed ore zones. The overprinting of the two foliations by pentlandite and exsolution of pentlandite along the grain boundaries of flattened pyrrhotite grains suggest that the Garson ores reverted to a metamorphic monosulfide solid solution at temperatures ranging between 550 and 600 °C during D₁ and continued to deform as a monosulfide solid solution during D₂.     

Instantaneous Friction Angle and Cohesion of 2-D and 3-D Hoek–Brown Rock Failure Criteria in Terms of Stress Invariants

The Mohr–Coulomb (M–C) failure criterion is one of the most widely used failure criteria in rock mechanics, although it has a number of shortcomings such as neglecting the nonlinear strength observed in rock or the effect of the intermediate principal stress σ ₂. Other failure criteria have been proposed to effectively include in the predictions of failure the non-linear response of rock to confinement or the effects of the intermediate principal stress. The M–C criterion is still widely used, and it is arguably the criterion most used in practice. For example, stability evaluations of shallow rock structures such as slopes and foundations are routinely carried out by estimating a friction angle and a cohesion of the rock mass. To include the dependency of cohesion and friction angle on stresses, efforts are being made to estimate equivalent values of the M–C parameters for the range of stresses applicable to a particular design. The paper suggests a new and convenient approach to find the equivalent friction angle and cohesion from any failure criterion that can be expressed in terms of the Nayak and Zienkiewicz’s stress invariants. To demonstrate the capabilities and application of the methodology, the new approach is applied to two failure criteria: the Hoek–Brown (H–B) criterion and the Hoek–Brown and Willam–Warnke (HB–WW) criterion, 2-D and 3-D failure criteria, respectively. Results from the new method, in terms of equivalent friction and cohesion for the H–B criterion, are exactly the same as the results obtained from Balmer’s theory, which confirms the validity of the new method. The predicted equivalent friction and cohesion for the HB–WW criterion show a dependency on σ ₂, which does not occur for a 2-D failure criterion.     

Prediction of Large Deformation Behavior in Tunnels Based on AHP–FUZZY Method and Numerical Simulation Method

In this paper, two different research methods are applied to predict large deformation behavior in tunnels and take Tianjiashan tunnel as the case study which is located in Xindianping town, Zhejiang city, Hunan province. The paper introduces the basic principle of the analytic hierarchy process and the fuzzy mathematics method, and classifies the influence factors of the large deformation in tunnels into eight kinds (C1–C8). Basing on the AHP–FUZZY method, this paper applies the results into the large deformation prediction analysis of Tianjiashan tunnel. In order to verify the accuracy of the evaluation results of AHP–FUZZY method, a numerical simulation model of DK394 + 625–DK394 + 650 section of Tianjiashan tunnel is established. The results show that the tunnel deformation is very large, and the tunnel excavation is sure to cause large deformation. The numerical simulation result is in accordance with the AHP–FUZZY method. Finally, we track record of occurrence of large deformation during the actual construction in tunnel, and the actual results are coincide with AHP–FUZZY method and numerical simulation results, which reflects the effectiveness of AHP–FUZZY method and numerical simulation method in predicting the large deformation behavior in tunnels.     

Risk Assessment of Coal Floor Water Inrush from Underlying Aquifers Based on GRA–AHP and Its Application

Ground water inrush from underlying coal seam aquifers is a serious geohazard during coal mining in China. In order to effectively predict coal floor water inrush, the evaluation index system and evaluation standard for coal floor water inrush, containing quantitative indexes and qualitative indexes, is established on the base of conditions of aquifer and aquiclude, geologic structure and mining disturbance. Simultaneously, grey relational analysis and analytic hierarchy process are used to establish an evaluation model which efficiently overcomes the uncertainty between indexes of water inrush effects and really reflects the degree of importance for each index of water inrush effects. The model is applied to the typical working face of Yuzhou coalfield in the north of China to demonstrate the evaluation process. Compared to the water inrush coefficient method which is widely used for evaluating coal floor water inrush, the presented evaluation model in this paper accords more with the susceptibility of coal floor water inrush by multi-factor and is of nonlinear dynamic characteristics of highly complicated formation mechanism. This method offers a new tool in the assessment of ground water inrush in mine.     

Statistical Models of Temperature in the Sacramento–San Joaquin Delta Under Climate-Change Scenarios and Ecological Implications

Changes in water temperatures caused by climate change in California’s Sacramento–San Joaquin Delta will affect the ecosystem through physiological rates of fishes and invertebrates. This study presents statistical models that can be used to forecast water temperature within the Delta as a response to atmospheric conditions. The daily average model performed well (R ² values greater than 0.93 during verification periods) for all stations within the Delta and San Francisco Bay provided there was at least 1 year of calibration data. To provide long-term projections of Delta water temperature, we forced the model with downscaled data from climate scenarios. Based on these projections, the ecological implications for the delta smelt, a key species, were assessed based on temperature thresholds. The model forecasts increases in the number of days above temperatures causing high mortality (especially along the Sacramento River) and a shift in thermal conditions for spawning to earlier in the year.     

Seismotectonic Deformation of Active Segments of the Junction Zone of the Kolyma–Omolon Superterrane and South Anui Suture (Southeastern Russia)

Geotectonics - Our seismotectonic studies focus on active segments of the junction zone of the Kolyma–Omolon superterrane and the South Anui suture. The aim of our research is to identify...     

Interpretation of Soil–Cement Properties and Application in Numerical Studies of Ground Settlement Due to Tunneling Under Existing Metro Line

Uncertainty of properties of improved soft ground with chemical grouting often results in discrepancy between simulated results and observed data and makes prediction for ground subsidence difficult. It also made practice usually adopts unconfined compressive strength of soil–cement mixtures as design control criterion. This paper presents a methodology to interpret the strength and deformation parameters from unconfined compressive strength of soil–cement mixtures for advanced numerical analysis which is widely used in reinforcing the soft ground and pre-supporting excavation. Observed data are used to compare with the simulated results and validate the interpretations. Numerical experiments with two-dimensional finite element model for covered undercutting of large cross-sectional twin tunnel under an existing subway station are presented. Issues with respect to design and construction of excavation that potentially affect the ground surface subsidence are explored. It was found that the ground subsidence caused by tunneling in soil–cement medium under existing subway station is similar to that in a greenfield site but with flatter settlement trough. Unconfined compressive strength of soil–cement mixtures ranging from 1.5 to 2.0 MPa can significantly reduce the settlement to an acceptable control criterion. Settlement magnitude is influenced by pillar width but not obviously by the location of umbrella arch installed in twin tunnels.     

Structural Setting and Heterogeneous Deformation of the Mesoproterozoic Granite–Gneisses of North Tianshan with the Example of the Karadjilga Massif (Kyrgyzstan)

Doklady Earth Sciences - A detailed structural study showed that the Mesoproterozoic Karadjilga granite–gneiss massif of the Kyrgyz North Tianshan represents a sheet intrusion, concordant to...     

Coal pore characteristics at different freezing temperatures under conditions of freezing–thawing cycles

Most coal reservoirs in China have low permeability, which causes gas drainage to be inefficient. The method of cyclic cryogenic fracturing basing on freezing–thawing (F–T) fracturing effects is proposed to break coal to increase its permeability. An F–T experiment was carried out at different freezing temperatures using a nuclear magnetic resonance (NMR) test and an ultrasonic test. We investigated the evolution of coal pore structure under different freezing temperature F–T cycles and the mechanism of F–T fracturing. The results indicate that the frost force and the thermal stress in the cyclical process of F–T work together to cause fracture formation and fatigue damage. When the freezing temperature decreases, the network of pores and fissures becomes more developed and the number of mesopores, macropores and micro-fractures increases. This suggests that the network of pore-fractures in coal will be more interconnected and the space available for gas seepage will be larger. Ultimately, this significantly increases the efficiency of gas drainage.     

Effects of Coal Rank and High Organic Sulfur on the Structure and Optical Properties of Coal-based Graphene Quantum Dots

Coal‐based graphene quantum dots (GQDs) were successfully produced via a one‐step chemical synthesis from six different coal ranks, from which two superhigh organic sulfur (SHOS) coals were selected as natural S‐doped carbon sources for the preparation of S‐doped GQDs. The effects of coal properties on coal‐based GQDs were analyzed by means of high‐resolution transmission electron microscopy (HRTEM), X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X‐ray photoelectron spectroscopy (XPS), ultraviolet‐visible (UV‐Vis) absorption spectroscopy, and fluorescence emission spectra. It was shown that all coal samples can be used to prepare GQDs, which emit blue‐green and blue fluorescence under ultraviolet light. Anthracite‐based GQDs have a hexagonal crystal structure without defects, the largest size, and densely arranged carbon rings in their lamellae; the high‐rank bituminous coal‐based GQDs are relatively reduced in size, with their hexagonal crystal structure being only faintly visible; the low‐rank bituminous coal‐based GQDs are the smallest, with sparse lattice fringes and visible internal defects. As the metamorphism of raw coals increases, the yield decreases and the fluorescence quantum yield (QY) initially increases and then decreases. Additionally, the surface of GQDs that were prepared using high‐rank SHOS coal (high‐rank bituminous coal) preserves rich sulfur content even after strong oxidation, which effectively adjusts the bandgap and improves the fluorescence QY. Thus, high‐rank bituminous coal with SHOS content can be used as a natural S‐doped carbon source to prepare S‐doped GQDs, extending the clean utilization of low‐grade coal.