Search

As the main bearing structure of the reservoir in the goaf of the mine, the damage instability mechanism under the influence of multi-field coupling of water immersion directly restricts the long-term safe and stable operation of the reservoir in the goaf. In this paper, nuclear magnetic resonance (NMR)was used to study the T2 spectrum, pore throat, porosity change and nuclear magnetic image evolution of coal samples under different times of cyclic immersion under'unilateral' immersion conditions. With the increase of cyclic immersion times, the number of pores, pore throat ratio and porosity of coal samples maintained an increasing trend, which increased by 67.18%, 3.48% and 3.49% respectively. The nuclear magnetic resonance imaging further obtained the permeability and pore change law of water molecules in different times of unilateral cyclic immersion of coal samples: the water molecules in unilateral cyclic immersion of coal samples gradually flow from the immersion side to the internal of coal samples, and finally expand to the whole coal samples, further resulting in an increase in porosity. With the increase of cyclic soaking times, the uniaxial compressive strength and residual strength of coal samples decreased gradually. The average peak strength of coal samples decreased from 15.74 MPa to 11.76 MPa, 9.65 MPa and 8.41 MPa, respectively. The average uniaxial compressive strength of coal samples decreased by 46.56% compared with that of initial coal samples. The average residual strength decreased from 5.55 MPa to 3.08, 2.44 and 0 MPa, respectively. Long-term cyclic immersion has a significant softening effect on coal samples. Based on the experimental results, the evolution law of internal pores and the morphological characteristics of uniaxial compression failure of coal samples under the increasing number of unilateral cyclic immersion were analyzed, and the mechanism of water immersion damage and failure of coal samples was revealed. The experimental results provide a scientific basis for the stability control of reservoir spatial structure in goaf.

Coal is a porous material containing pore structures and mineral components, exhibiting pronounced anisotropy and size effects.In order to investigate the influence of coal anisotropy and size effects on its failure characteristics, this paper proposes a simulation method for characterizing and reconstructing three-dimensionally the internal pores and mineral components of coal samples based on CT scanning, nuclear magnetic resonance, and X-ray diffraction.Specifically, we obtained simulation parameters of three-dimensional reconstruction models of coal matrix and mineral components through inverse laboratory uniaxial compression experiments, while simulated and analyzed the strength damage characteristics of coal bodies with different aspect ratios.The simulation results show that: ① During the loading process, the plastic zone first gradually expands and connects outward around the pores and mineral components.In terms of spatial distribution, the plastic zone expands vertically from the loading end to the interior in the early stage, and in the later stage, it expands horizontally from the surroundings to the interior.After the model is damaged, a "double truncated cone structure" is formed in the non-plastic zone.② The increase of aspect ratio leads to an increase in the compressive strength(p) of coal samples, the strain(ζ) at yielding strength, and the elastic modulus(K), among which ζ and K increase linearly, while the margin of increase in p gradually decreases.③ The total energy and elastic energy of coal sample loading increase exponentially, while the dissipated energy increases linearly.The increase of aspect ratio leads to an increase both in the accumulated elastic energy in the coal body and in the released energy during failure, which easily induce dynamic impact-related disasters.This study provide references for the reasonable selection of coal pillar size in impact mine pressure area.

Research on the dissolution effect and the water purification mechanism of fractured coal and rock mass in the goaf area of underground reservoir is the key to realizing the safe and efficient operation of underground reservoir in mine.This paper takes the underground water reservoir formed by the mining of 31409 working face in Jinjie coal mine as example, and selects the broken coal rock mass in the mining area and deionized water for the experimental study of pollutant release law.We analyse the law of dissolution action of broken coal rock mass in the mining area, and explore the mechanism of the influence broken coal rock mass exerts on the characteristics of the water body.We discover the law of pollutant release of broken coal rock mass under different temperature and weathering degrees, and analyse precipitation and dissolution that occurs during the water purification process in underground water reservoir.The water-rock interaction of dissolution, the adsorption and precipitation of clay mineral surfaces and soluble organic matter in the rock body constitute the water purification characteristics of the groundwater reservoir, with dissolution, adsorption and precipitation each playing a dominant role in influencing mine water quality at different time scales.

Coal seam mining causes deformation, fracture and migration of overlying rock, further leading to the surface subsidence and ecological damage, which are the main manifestations of mining damage.Quantitatively characterize mining damage is the key to analyzing the stability of surrounding rock, designing mining parameters, and the premising of roadway support parameters.According to the finite element and discrete element simulation methods commonly used at this stage, this paper proposes a quantitative index(damage degree)to characterize mining damage: the proportion of zone plastic volume and the proportion of contact fracture length(number).On this basis, this study carried out the optimization of high-intensity mining parameters of the western mining area, the stability analysis of the coal pillar under the condition of mining and water immersion, and the progressive damage characteristics analysis of the roadway surrounding rock in the water-filled fault structure area by using the damage degree index.The quantitative relationship between the damage degree of the overlying rock and the mining parameters is obtained, which can realize the reasonable optimization of the mining parameters.This paper revealed the progressive damage characteristics of mining water immersion in coal pillars.We deemed that there is a danger of water seepage in the mined-out area as a water storage area under the existing coal pillar conditions.This study quantified the damage distribution characteristics of the surrounding rock in the roadway in the water-filled fault structure area, and proposed the corresponding? solution of dredging the fault through the roof aquifer, grouting reinforcement of the original fault fracture and strengthening the support.By comparing with common indicators such as the height of the water-conducting fracture zone and the width of the plastic development of the coal pillar, this research found that the damage degree indicators are more sensitive to the characterization of mining damage, and could realize continuous mining damage characterization.

The age-related decline in T-cell function among elderly individuals remains unclear. We thus investigated the interrelationship between T-cell subsets and age to identify the changes in T-cell phenotypes and develop an age prediction model for the elderly population. A total of 127 individuals aged >60 years were divided into three groups (youngest-old group, 61–70 years, n = 34; middle-old group, 71–80 years, n = 53; and oldest-old group, ≥ 81 years, n = 40). The percentage of CD8+CD28− cells (P = 0.001) was highest in the oldest-old group and then followed by the middle-old group, while the youngest-old group was the lowest. Both females and males demonstrated significant decreases in the absolute counts of CD4+CD45RA+ cells (P = 0.020; P = 0.002) and CD8+CD28+ cells (P = 0.015; P = 0.005) with age. Multivariate linear regression showed that the percentage of CD8+CD28− cells (P < 0.001) was an independent predictor of aging after adjusting for sex, body mass index, hospitalization duration, smoking, drinking, chronic medical illness, and medications at admission. In conclusion, our results suggest that aging in elderly individuals is accompanied by a decrease in the counts of T-cell subpopulations. CD8+CD28− cells may be potential targets for elderly individuals in antiaging-related immunosenescence.

In order to obtain the fracture development characteristics of the working face with extra-large mining height under the condition of thick overburden and medium mining depth in mining areas in China's western regions, this paper adopted a comparative study by combining empirical equations, numerical simulation and field measurement in the panel 12401 of the Shangwan coal mine.The results show that the empirical equations drawn from data from the typical geological conditions of mining areas in eastern and western China are difficult to apply to this panel with extra-large mining height, thick overburden and medium buried depth.The prediction values of the empirical equations based on data from the geological condition in the western mining regions are generally higher, which are significantly smaller in the eastern mining regions.The value predicted by the numerical simulation based on the damage constitutive model is closer to the measured value than those derived from using empirical equations, with a relative error of less than 5 %.The paper obtained the characteristics of the water-conducting fracture zone development: due to the existence of soft and hard rock in the overburden, the water-conducting fracture zone develops upward as a step, and the shape changes from "arch"(three-dimensional "shell") to "saddle"(three-dimensional "basin shape") with the variation of mining degree.

The height of overburden fissure zone is an important index to study the deformation and failure of overburden, but the existing single index can not reflect the fracture degree of surrounding rock in different space parts of stope. Based on 81505 working face of Baode Mine with typical shallow burial conditions in Shendong, the unification of coal sample damage degree and index RFD (Rock Failure Degree) is completed by laboratory experiments, and a similar model and a numerical model are constructed. Based on the index RFD, the maximum destructive depth in numerical simulation is extracted, and the law of development height of overburden mining fissure zone and its variation with mining height are studied by comparing similar simulation results. The results show that the index RFD can well assess the development characteristics of mining fissure zone under typical shallow burial conditions in Shendong. And the development height of fissure zone continuously with the increase of mining height but the growth rate decreases gradually. The research in this paper provides theoretical support and technical basis for distribution and destruction characteristics of fractured zones, occurrence of rock pressure and safe mining.

When the coal-seams are multi-layered, the stress and permeability of the caving zone are disturbed again during the following coal seam mining. Repeated unloading and compaction cause caved coal and rock to break further in the caving zone, which in turn affects the migration of gas in goaf. This paper briefly summarizes prior research on caving zone internal stress, porosity, permeability and other parameters of the process of longwall face advancing. The forecast methods for calculating the stress and permeability of the caved zone during its compaction are listed. On the basis, this paper describes a laboratory experiment of the broken coal and rock in the caving zone of the gob in Huainan coal mine. The laboratory test results imply that the re-crushing, re-arrangement, and compressional deformation of particles in the loading process lead to a drastic drop in the caving zone porosity, which causes the permeability reduction. The permeability sensitivity to stress of broken rock (broken coal) samples was determined by their strength. The greater the proportion of coal samples in the combined coal and rock samples, the higher the permeability stress sensitivity and the smaller the permeability.With the increase of the cyclic times, the stress sensitivity gradually weakened. Based on laboratory experiments, the stress-permeability fitting model of the broken coal and rock in the caving zone during the group coal seam mining is proposed in this paper.

The coupling characteristics of coal seam stress,fracture and seepage directly affect the migration characteristics of pressure relief gas during the protective seam mining.In this paper,combined with cubic law,the method for the selection of the fluid solid coupling parameters of elastic joints and persistent fracture was proposed based on the experimental data of the elastic and persistent fracture coal samples.Meanwhile,the simulation modeling of fluid solid coupling for triaxial flow test of coal samples was built.On the basis of this simulation method,the coupling characteristics of the coal sample stress,fracture and flow were simulated and analyzed during uniaxial and triaxial loading.The simulation results show that the permeability of coal samples changes as S type with the increase of axial strain.The permeability of coal sample decreases gradually with the increase of axial pressure before the fracture of coal sample development.The permeability of the coal samples increases with the development of the fractures,and the faster the fracture expansion rate is,the higher the permeability increases.The increase of confining pressure resulted in the decrease of internal fracture generation and propagation,and the permeability reduction stage was extended.The initial permeability and yielding permeability of the coal samples decreased gradually.

C43H35CuINP2S2, triclinic, P1¯ (no. 2), a = 10.6136(8) Å, b = 12.406(1) Å, c = 16.729(1) Å, α = 96.807(1)°, β = 98.279(1)°, γ = 113.245(2)°, V = 1965.3 Å3, Z = 2, Rgt(F) = 0.0314, wRref(F2) = 0.0828, T = 298 K.

C62H74Ag2O8P4, monoclinic, P21/n (no. 14), a = 10.024(1) Å, b = 17.888(1) Å, c = 17.730(2) Å, β = 106.233(2)°, V = 3052.3 Å3, Z = 2, Rgt(F) = 0.0531, wRref(F2) = 0.1483, T = 298 K.