Structure Of Strata Research Articles

Study of the Stability Control of Rock Surrounding Longwall Recovery Roadways in Shallow Seams

The rock pressure appearance of longwall faces in shallow seams is generally violent, and roofs and supports are susceptible to damage during equipment extraction. Stability control of the rock surrounding longwall recovery roadways allows safe and rapid equipment extraction. Herein, via theoretical analysis, numerical simulations, and field observations, the stability control of the rock surrounding recovery roadways is studied to ensure the release of the accumulated rock pressure on the roof, the working resistance of the supports and the reasonableness of the recovery roadway support design. Pressure-relief technology is introduced to release the accumulated rock pressure before equipment extraction, and a discriminative approach is proposed to determine the breaking and articulated forms of key strata and broken blocks, respectively. On this basis, mechanical models of roof instability are established based on four key stratum structures in the overburden of shallow seams. Methods for calculating a reasonable working resistance for supports are discussed. Finally, Liangshuijing Coal Mine and Fengjiata Coal Mine are taken as research objects to evaluate the roof stability of recovery roadways based on observations of weighting characteristics. The support working resistances and reasonable recovery roadway widths under three key stratum structures are determined. Considering the time effect of plastic zone development, the support design of recovery roadways is optimized. FLAC2D software simulates the surrounding rock control effect of two support designs, and roof subsidence curves are obtained. The results show that the key to equipment extraction in shallow seams is to ensure that supports have reasonable working resistances and to improve the support of recovery roadways. The results provide a reference for the selection and extraction of supports in shallow seam faces.

Descripción del estrato arbóreo en combinación con café rustico en una selva mediana subperennifolia, Jocotepec, Oaxaca

Los sistemas agroforestales (SAF) de café son consideradas áreas que incrementan la biodiversidad de especies tanto de flora y fauna, son fuentes de ingresos económicos para las comunidades que los trabajan, así como de múltiples servicios ambientales. Con el objetivo de conocer la influencia del manejo en los SAF de café en la diversidad de especies arbóreas, se describió la composición, estructura y diversidad del estrato arbóreo en dos cafetales rusticanos, bajo condiciones de manejo: cafetal activo (CA) y cafetal abandonado (CAb), en Jocotepec, región Costa de Oaxaca. En cada condición de manejo se situaron cuatro unidades de estudio de 20 × 30 m (0.06 ha). A todos los individuos arbóreos a partir de 1.30 m del suelo se les registró el diámetro normal (DN) ≥ 2.5 cm, altura total y cobertura de copa. Se evaluó la riqueza, estructura vertical, horizontal, Índices de Valor de Importancia y Forestal (IVI e IVF); diversidad con los Índices de Simpson modificado por Pielou (1-D) y Shannon-Weaver (H´) y la equidad (E), dominancia (D) y Similitud. Se obtuvo una riqueza de 35 especies para el CA y 31 en CAb; las principales familias taxonómicas fueron Fabaceae, Lauraceae y Moraceae. En ambas condiciones de manejo la categoría diamétrica 5 (2.5‑7.5 cm) superó en número de individuos arbóreos, con una distribución de alturas que reveló la existencia de dos estratos verticales. Las especies que presentaron un alto IVI e IVF en CA fueron: Cedrela odorata, Tabebuia rosea y Quercus crispifolia y para el CAb: Quercus sp., Ficus tecolutensis y Ocotea helicterifolia. Entre CA y CAb no se presentaron diferencias en las variables evaluadas, 1-D, H´, E y D. La similitud florística entre condiciones fue del 52%.

Construction of Ti3C2 MXene@C@SnS with layered rock stratum structure for high-performance lithium storage

Tin sulfide (SnS) possesses high theoretical capacity and make it a very potential anode material for lithium-ion batteries. Nevertheless, the poor electrical conductivity of SnS is prone to collapse during lithiation/de-lithiation. Herein, Ti3C2 MXene@C@SnS hybrids with layered rock stratum structure are prepared as an anode electrode for lithium ion batteries through hydrothermal and subsequent annealing. The hybrids integrate large specific surface area and porosity, and accelerate electron/ion transfer. The Ti3C2 MXene@C@SnS anode exhibits a superior capacity (1473 mA h g−1 at 0.1 A g−1), outstanding rate capability (640 mA h g−1 at 5 A g−1 and keeps 1142.2 mA h g−1 for 70 cycles returning to 0.5 A g−1 again) and excellent long-cycle stability (1050 mA h g−1 at 1 A g−1 over 350 cycles). Kinetic analysis reveals that the excellent rate capability is controlled by surface pseudocapacitance behavior at high current. This result indicates that Ti3C2 MXene@C@SnS can be potentially applied in the field of lithium storage.

Study on the structural forms of the key strata in the overburden of a stope during periodic weighting and the reasonable working resistance of the support

AbstractMany mines often passively select supports with a higher yield load to avoid the occurrence of support crushing and roof falling during periodic weighting. This method is not conducive to improving production efficiency or reducing mining costs, but it can ensure safe mining. An effective method for overcoming these problems is to determine the reasonable working resistance of the support according to the structural forms of the key strata in the overburden of the stope during periodic weighting. In this paper, comprehensive theoretical analysis, numerical simulation, and field observation were applied to study the discrimination of the key stratum structure (KSS) during periodic weighting and the calculation method of the support load. First, the KSS that affects the periodic weighting of the stope was classified. The “twice discrimination method” was proposed for determining the breaking form of the key strata and the articulated form of the broken blocks. On this basis, the spacing condition that determines whether adjacent key strata interact was analyzed. The discriminant conditions for synergistic breaking between the first subordinate key stratum (SKS1) and the upper key stratum were derived for the cases in which the SKS1 periodically breaks in the form of a cantilever beam, a voussoir beam, and a step beam. These conditions provide the basis for distinguishing the KSS in the overburden of the stope. In addition, mechanical models of the roof structure during periodic weighting were established, and general formulas for calculating the support loads of stopes with a single‐key‐stratum influence structure and a multikey‐stratum influence structure were presented. Finally, five fully mechanized coal faces with various mining conditions in China were considered for engineering verification. The results of this study demonstrate that the proposed method for determining the reasonable working resistance of the support is consistent with the field practice. The research results can provide a reference for roof control and support selection of stopes.

Statistical inference using stratified judgment post-stratified samples from finite populations

This paper develops statistical inference for population mean and total using stratified judgment post-stratified (SJPS) samples. The SJPS design selects a judgment post-stratified sample from each stratum. Hence, in addition to stratum structure, it induces additional ranking structure within stratum samples. SJPS is constructed from a finite population using either a with or without replacement sampling design. Inference is constructed under both randomization theory and a super population model. In both approaches, the paper shows that the estimators of population mean and total are unbiased. The paper also constructs unbiased estimators for the variance (mean square prediction error) of the sample mean (predictor of population mean), and develops confidence and prediction intervals for the population mean. The empirical evidence shows that the proposed estimators perform better than their competitors in the literature.

Key Stratum Structure and Support Working Resistance of Longwall Face with Large Mining Height in the Shallow Coal Seams, China

The fully mechanized mining with large mining height is the main method for high yield and efficient coal mining in China. The key stratum structure (KSS) is the basis of revealing the mechanism of roof weighting and determination of support working resistance of the longwall face with large mining height (LFLMH) in the shallow coal seam. The height of the caving zone at LFLMH is large, the thick immediate roof forms the “short cantilever beam” structure commonly, and the hinge layer of the overlying key stratum will move upward to the higher position. The “high position oblique step voussoir beam” structure of single‐key stratum (SKS) and “oblique step voussoir beam and voussoir beam” structure of double‐key stratum (DKS) in the shallow coal seam were proposed with physical simulation and Universal Distinct Element Code (UDEC). The analysis of the KSS and numerical simulation reveals the mechanism of strong roof weighting at the SKS longwall face and large‐small alternate periodic weighting at the DKS longwall. It is concluded that the large static load caused by the “equivalent immediate roof (EIR)” is the basic load, and the instability load of the KSS is the additional dynamic load of support. Besides, the calculation methods of the reasonable support working resistance at LFLMH were obtained and verified with engineering applications.

Study on the generalized model of the lateral frictional resistance distribution under the ultimate state of the bored piles based on stratum structure

Based on the results of the ultimate load distribution of the part of the bored piles in the vertical static load field test of single pile, combined with the analysis of the relevant piles and soil data, found that the lateral friction resistance distribution of the bored pile in the ultimate load state was mainly related to structure of the soil layer on the pile side. Based on this, the side resistance distribution mode of the pile under the ultimate load conditions is generalized into a trapezoid, wing-shaped, micro-arc, and “R” shaped. The lateral friction resistance of the pile is positively correlated with the hardness of the soil, and the depth, thickness can influence the pattern of distribution of lateral friction resistance.

НЕФОРМАЛЬНАЯ ЗАНЯТОСТЬ КАК ИСТОЧНИК ФОРМИРОВАНИЯ ПРЕКАРИАТА В РОССИИ: МЕТОДОЛОГИЯ ИССЛЕДОВАНИЯ И ОЦЕНКА ПОТЕНЦИАЛА

The article presents the results of studies of the content, structure of sources and conditions for the emergence, growth and development of a new social stratum – the precariat – in Russia. The essential content of this layer, its main characteristics, forms of manifestation, possible consequences of its development are described. The fact is noted that this new social stratum, claiming to be a class, carries a protest potential, which, for the time being, can be weakened. For this, it is necessary to know the structure and content of the sources of formation of this layer in Russia, the conditions for its growth and development. In this regard, a methodology for researching the precariat in Russia has been developed and proposed, the results of researching the potential of one of the sources of its formation and replenishment, namely informal employment, are presented. The results of a survey carried out by the method of expert interviews of one of the groups of informally employed workers, which make it possible to judge about the formation of the structure of this social stratum, are also presented. The results of the study allow concluding that, in Russia, the precariat, as a new socially dangerous stratum, has a material base for its formation, growth and development in the form of informal employment. It is necessary to take appropriate measures to limit this base in order to reduce the protest potential in society. The development of these measures requires further in-depth research, which can be based on the proposed methodology.

Increased 1-Deoxysphingolipids and Skin Barrier Dysfunction in the Skin of X-ray or Ultraviolet B Irradiation and Atopic Dermatitis Lesion Could Be Prevented by Moisturizer with Physiological Lipid Mixture.

BackgroundSkin diseases characterized by epithelial barrier dysfunction show altered sphingolipid metabolism, which results in changes in the stratum corneum intercellular lipid components and structure. Under pathological conditions, 1-deoxysphingolipids form as atypical sphingolipids from de novo sphingolipid biosynthesis.ObjectiveThis study investigated the potential role of 1-deoxysphingolipids in skin barrier dysfunction secondary to X-ray and ultraviolet B (UVB) irradiation in vitro and in vivo. It was also evaluated changes in the expression of 1-deoxysphingolipids in lesional human skin of atopic dermatitis.MethodsIn this study, the changes in these 1-deoxysphingolipids levels of skin and serum samples were investigated in skin barrier dysfunction associated with X-ray and UVB irradiation in vitro and in vivo.ResultsIncreased 1-deoxysphingolipids were observed in cultured normal human epidermal keratinocytes after X-ray irradiation. X-ray or UVB irradiation increased the production of 1-deoxysphingosine in a reconstituted 3-dimensional (3D) skin model. Interestingly, treatment with a physiological lipid mixture (multi-lamellar emulsion contained pseudoceramide), which can strengthen the epidermal permeability barrier function, resulted in decreased 1-deoxysphingosine formation in a reconstituted 3D skin model. Further investigation using a hairless mouse model showed similar preventive effects of physiological lipid mixture against 1-deoxysphingosine formation after X-ray irradiation. An increased level of 1-dexoysphingosine in the stratum corneum was also observed in lesional skin of atopic dermatitis.Conclusion1-deoxysphingosine might be a novel biomarker of skin barrier dysfunction and a physiological lipid mixture treatment could prevent 1-deoxysphingosine production and consequent skin barrier dysfunction.

The Key Stratum Structure Morphology of Longwall Mechanized Top Coal Caving Mining in Extra‐Thick Coal Seams: A Typical Case Study

Longwall mechanized top coal caving mining (LMTCCM) in extra‐thick coal seams has its own characteristics. The law of mining pressure and overlying strata failure height in extra‐thick coal seams are much larger than those of medium‐thick and thick coal seams. The key stratum structure morphology also has an important influence on the law of overlying strata movement and stability of surrounding rock. Based on the engineering geological conditions, this paper used the method of theoretical analysis and numerical simulation to study the key stratum structure morphology of LMTCCM in extra‐thick coal seams. The results show that under the condition of LMTCCM in extra‐thick coal seams, the key stratum forms the structure of low cantilever beam and high hinged rock beam. With the increase of coal seam thickness, the breaking position of cantilever beam is closer to the coal wall. Through theoretical calculation, it is obtained that the breaking length of cantilever beam is 31.5 m and the breaking position of cantilever beam is 15.4 m away from coal wall. With the increase of cycle, key strata will undergo the evolution law from the generation of longitudinal cracks to the hinged structure and then to the cantilever beam structure. The breakage of key strata will cause the expansion of longitudinal cracks and the overall synchronous movement of overlying strata. With the increase of coal seam thickness, the distribution of longitudinal cracks will gradually transfer from the upper part of goaf to the deep part of coal body in space and increase in quantity. This research is of great significance for improving the stability of overlying strata and ensuring the safe and efficient mining of extra‐thick coal seams.

Numerical Simulation and Model of Deformation Features of Destabilized Mining Slope Under Fault-Controlled Conditions

This paper took the Fengmaoding slope, typically found in the mountainous areas of central Shanxi province, as its research area. The stratum structure of the Fengmaoding slope is a typical coal measures stratum covered by a layer of loess. There are communication towers on the slope mass and top of the slope; railways, roads, and rivers at the foot of the slope. There are many villages across from the slope, therefore, the buildings and structures nearby, even the lives of the villagers are threatened by the damages caused by the deformation of the slope. Tectonic development and mining activities have very profound effects on the stability of the slope. Considering the above, this paper analyzed the effects of the fault in controlling the deformation features of the destabilized slope during underground mining by adopting the method of numerical simulation from these perspectives including displacement, stress, strain, among others. under different circumstances (the faulted and unfaulted) so as to provide guidance for future studies about landslides of the same type and give preventive proposals for reference.

Study on hydrocyclone used for natural gas hydrate mining

Nowadays, energy shortages and global environmental pollution problems are becoming increasingly prominent, and the exploration of clean and renewable energy has become an important direction of energy research. Natural gas hydrates have become the most promising alternative energy source in the future due to its advantages of high calorific value, small environmental hazards and abundant mineral deposits. About 99% of natural gas hydrates are stored in the seabed formation. In 2014, China proposed solid-state fluidized mining technology for marine natural gas hydrates. One of its key technologies is to remove sand from hydrates in real time and backfill the sand on the seabed. Therefore, a downhole axial hydrocyclone suitable for the exploitation of marine natural gas hydrates is proposed in this paper. The purpose of this study is to achieve real-time sand removal and backfilling of downhole hydrate mixed slurry, reduce the sand content of produced fluid, protect the seabed stratum structure, and at the same time reduce the energy consumption of pipeline transportation. In this study, the experimental method was used to evaluate the separation performance of the cyclone with a nominal diameter of 100 mm under different working conditions.

Sliding instability characteristics and re-stabilization mechanism of key stratum in thin-topsoil SCS mining: a computer-aided case study from the Niushan Coal Mine, China

Roof step subsidence and support crushing accidents caused by the sliding instability of fractured single key stratum often occur in shallow coal seam (SCS). For this reason, the exploration of fracture displacement laws and control mechanism of key stratum in thin-topsoil SCS is of great significance for both roof control and safety production. From this perspective, in this study, numerical simulation and theoretical analysis were conducted to establish a mechanical model of the key stratum structure after sliding instability in thin-topsoil SCS. Moreover, its instability characteristics and re-stabilization control mechanism were analyzed. The results revealed that the fractured key stratum block could reach re-stabilization without any support crushing after sliding instability in thin-topsoil SCS depending on the significant unloading effect of the topsoil. The mechanical model of the key stratum structure after sliding instability was also analyzed to obtain the criterion for the re-stabilization of the sliding instable rock block. The computational analysis corroborated that increasing the support intensity could promote the re-stabilization of fractured key stratum block after sliding instability, and the required support working resistance could be obtained for preventing support crushing incidents.

Research on Tunnel Lining Cavity Treatment Technology of a Metro Tunnel in Chongqing

The hollowing problem of tunnel lining structure is like a suspended bomb, which may affect the safety of vehicles and the safety of passengers at any time. Therefore, the study of tunnel lining structure cavity management technology has great social significance for ensuring tunnel safety. Taking a metro tunnel in Chongqing as an example, this paper proposes a reasonable lining structure reinforcement scheme of changing partial arches and reinforcing by steel strips after analyzing the environment, the bearing requirements, and the size and location of cavities. Based on the calculation formula of flexural members given by Code for Design of Concrete Structure Reinforcement, reduction system is introduced to calculate safety coefficient of flexural and compression members. The minimum value of structural bearing after treatment is 4.4, which meets the requirement of bearing capacity. Stratum structure method is used to calculate surrounding rock deformation during reinforcement. The maximum horizontal displacement is 1.9 mm, and the vertical displacement is 6 mm. The surrounding rock could be stable when treating defects, and the treatment scheme meets the requirements of bearing capacity and inner clearance. Therefore, the tunnel lining structure cavity can be reinforced by means of shotcrete and steel strips, without interrupting traffic and ensuring driving safety. The success of the treatment provides a useful reference for other similar projects.

Survey on roof movement of the gangue backfill working face

This paper studied the roof movement characteristics of LW1302N-1 with gangue backfill mining in Shandong Xinjulong Company of China. The monitoring of roof subsidence of the gob and bearing stress of filled gangue was carried out by using the roof subsidence and gangue loading monitoring system. From data analysis, the result shows that: (1) Gob roof subsidence can be divided into six stages including slow subsidence, fast subsidence, very fast subsidence, subsidence slowing down, subsidence speeding up and subsidence becoming slow. (2) Filled gangue loading period can be divided into four stages including slow increasing resistance, fast increasing strength, strengthening and continuing increasing resistance, Similarly, the gob roof movement consists of four steps such as immediate roof caving, central roof flexure, main roof fracturing, and high strata flexure. (3) The immediate roof is 3.1 times the thickness of equal mining height, and the main roof is 2.7 times the thickness of equal mining height. The research results provide a reference to the analysis of the characteristics of overlying strata structure and roof movement for gangue backfill mining in deep coal mines.

Numerical simulation of the short- and long-term production behavior of the first offshore gas hydrate production test in the South China Sea

Gas hydrate-bearing sediments at the first offshore gas hydrate production test site in the Shenhu area, South China Sea, have the characteristics of high irreducible water saturation and low permeability. The stratum structure of this production test site is complex, its gas hydrate-bearing layer (GHBL), three-phase layer (TPL) and free gas layer (FGL) all contain methane gas or gas hydrates, that make the production more complicated. According to the available geological data at the first offshore gas hydrate production test site in the Shenhu area, a 2D numerical simulation model is built to study the short- and the long-term production behavior of the gas hydrates in the Shenhu area. In the short-term, the total gas production from hydrates, when the TPL gas saturation is 0.078, is determined to be 2.75 × 105 m3, which is close to the actual total gas production of 3.09 × 105 m3. When the irreducible water saturation varies from 0.40 to 0.63, the total gas production changes from 1.41 × 105 to 2.75 × 105 m3, and the total water production decreases from 1.04 × 104 to 8.7 × 103 m3, which indicates that irreducible water is a favorable factor for gas production from hydrates in clayey silt sediments. In the long-term gas production from hydrates, the gas production rate first decreases, then increases, and finally decreases again. Gas hydrate reformation occurs at the interface between the TPL and the FGL, which will adversely affect the gas production from hydrates.

A LANDSLIDE PREDICTION MODEL BASED ON LOAD-UNLOAD RESPONSE RATIO THEORY AND ITS APPLICATION

Landslide is one of the most common geological disasters that seriously threatens human production and life. Hence it is of great significance to accurately predict landslide disasters. However, the process of landslide is accompanied by a series of extremely complex mechanical reactions, which are determined by various factors, such as the strength of rock and soil, the attitude and structure of stratum, the external disturbances and so on, and these factors are difficult to accurately capture. To predict the landslide accurately, a comprehensive landslide forecast model was proposed based on the load-unload response ratio (LURR) theory. In this model, sliding force inside the slope and displacement of the slope surface as the key parameters were measured. The sliding force, as the load-unload parameter, was obtained by a sliding perturbation remote monitoring (SPRM) system. While the displacement, as the load-unload response parameter, was measured by total station. Besides, the velocity and acceleration of displacement were also used as parameters to improve the accuracy of landslide hazard prediction. The LURR landslide prediction model was applied in Antaibao and Pingzhuang west open-pit slopes. Results show that the proposed model is accurate and reliable for landslide prediction. The force-displacement coupling model is more efficient in landslide prediction and early-warning, which is helpful to track the causes of landslide. Keywords: Landslide prediction, Load-unload response ratio, Sliding force, Remote monitoring

Structural Slip Model for Coal Bumps and the Effect of Coal Weakening Under Three-Hard Condition

Coal bump refers to a sudden catastrophic failure of coal seam and coal burst into underground mining roadway, while typical shallow-focus coal bumps in China generally happened under a three-hard strata structure. In order to clarify the mechanism of coal bumps caused by mining effect under the condition of hard coal-rock strata structure, a modified structural slip model is built considering coordinated deformation of roof and floor. The practical parameters of the Xinzhouyao coal mine are used to prove the validity of the model, then the vertical stress and the state of plastic zone under high stress are discussed with different strength reduction coefficients. The results show that the length of plastic zone is 1.5 m, 1.8 m, 2.3 m, 2.9 m respectively when the lateral pressure coefficient is 0.6, 0.9, 1.2, 1.5, with vertical peak stress ranging from 21.5 to 14.1 MPa, and that the model could well reflect the stress distribution and bump risk with stress status. By discussing the effect of weakening of coal seam, the structural slip mode of coal seam induced by mining effect are evaluated, the model can provide support for following risk evaluation and control.

Application of the Fisher Optimal Segmentation Method in MT Interpretation: A Case Study from Qiangtang Basin, Qinghai -Tibet Plateau

The development and construction of thrust faults in mountain front areas are quite complicated, causing interpretation difficulties with electrical resistivity. To address these difficulties, an optimal stratification method involving magnetotellurics (MT) was applied, based on Fisher's clustering method for continuous data. The feasibility and effectiveness of this method are verified by applying it to the MT exploration data in Qiangtang Basin, Qinghai-Tibet Plateau, China. The results show that the optimal stratification method can improve the resolution of the resistivity model effectively in areas with complex structures. The MT inversion section after optimal stratification reflects the stratum interface, fault and structure style more directly and can be used for comparison with seismic data. The Fisher segmentation method can be applied to the interpretation of the MT data as a supplementary method, especially in the complicated structural belts, areas in which the geological structure and deformation information cannot be recognized effectively by conventional methods.

Study on Influence of Soil Hardness Change on Pile Bearing Capacity and Settlement in Single Bearing Layer of Pile End

The bearing capacity and settlement of the pile are indispensable in the calculation and verification of the pile footing, and the diverse bearing layers of the pile foundation will have different effects on the ultimate strength of the pile and the pile’s settlement. Because of the selectivity and transformability of stratum structure, how to optimize the selection and reinforcement of stratum structure is of great significance to the economy and safety of engineering. Therefore the FEM is used to analyze the Sutong Bridge (large-diameter super-long bored pile) as an example, and then the influence of soil hardness change on pile bearing capacity and settlement is studied.