In China's northwest coal mining area, the excavation of shallow buried thick coal seams has caused serious damage to the phreatic water layer and induced deterioration of the ecological environment. ...Backfilling is a basic method of controlling the loss of groundwater and reducing surface subsidence. In order to reduce the porosity of the backfill material and control the compression ratio of the backfill body, the grain gradation of the local aeolian sand was studied based on the geological conditions of the shallow buried coal seam in the Yulin mining area, Shaanxi province. Subsequently, aeolian sand was selected as the backfilling aggregate, and tests were implemented. The optimum proportion and slurry concentration of the backfill material were then obtained. The engineering application shows that the strength and stability of the backfill body based on the close packing theory can satisfy the requirements of supporting the overlying strata, and the integrity of overburden strata is competent. The maximum accumulated surface subsidence was measured to be 38mm, indicating that the aeolian sand-based backfill material in shallow and thick underground coal seam mining is able to protect the eco-environment and control the geo-environmental hazards, which are critical for the sustainable development of the mining industry and economic growth.
Violent movement of the roof rock and severe damage to the overlying strata occur in the large mined-out space left by rapidly advancing, high-intensity longwall coal mine extraction, as the goaf ...forms. Knowing the height of the fractured water-conducting zone (FWCZ) above the goaf is vital in the safety analysis of coal mining, particularly under a water body. The processes of overburden failure transfer (OFT) were analyzed for such high-intensity mining, divided into two stages: transmission development, and transmission termination. Rock failure criteria were used in theoretical calculations of the maximum lengths of ‘suspended’ (i.e., unsupported) rock strata, and of the maximum ‘overhang’ (i.e., cantilever) length of each stratum. Based on this, mechanical models of the unsupported strata and the overhanging strata were established. A new theoretical method of predicting the height of the FWCZ in this form of coal mining is put forward, based on OFT processes. A high-intensity mining panel (the 8100 longwall face at the Tongxin Coal Mine, Datong Coal Mining Group) was taken as an example. The proposed theoretical method, a numerical simulation method and an engineering analogy method were used to predict the height of the FWCZ. Comparison with in situ measurements at the Tongxin mine showed that the theoretical and numerical simulation results were in close agreement with measured data, verifying the rationality of the proposed approach.
Summary
Root system architecture responds plastically to some abiotic stresses, including phosphorus (P), iron (Fe) and water deficiency, but its response mechanism is still unclear. We cloned and ...characterized a vegetative β‐expansin gene, GmEXPB2, from a Pi starvation‐induced soybean cDNA library. Transient expression of 35S::GmEXPB2‐GFP in onion epidermal cells verified that GmEXPB2 is a secretory protein located on the cell wall. GmEXPB2 was found to be primarily expressed in roots, and was highly induced by Pi starvation, and the induction pattern was confirmed by GUS staining in transgenic soybean hairy roots. Results from intact soybean composite plants either over‐expressing GmEXPB2 or containing knockdown constructs, showed that GmEXPB2 is involved in hairy root elongation, and subsequently affects plant growth and P uptake, especially at low P levels. The results from a heterogeneous transformation system indicated that over‐expressing GmEXPB2 in Arabidopsis increased root cell division and elongation, and enhanced plant growth and P uptake at both low and high P levels. Furthermore, we found that, in addition to Pi starvation, GmEXPB2 was also induced by Fe and mild water deficiencies. Taken together, our results suggest that GmEXPB2 is a critical root β‐expansin gene that is intrinsically involved in root system architecture responses to some abiotic stresses, including P, Fe and water deficiency. In the case of Pi starvation responses, GmEXPB2 may enhance both P efficiency and P responsiveness by regulating adaptive changes of the root system architecture. This finding has great agricultural potential for improving crop P uptake on both low‐P and P‐fertilized soils.
In the current study, a series of laboratory triaxial loading and unloading experiments were conducted for the purpose of comprehensively understanding the effects on sandstone of loading processes ...under axial stress conditions and unloading processes under confining pressure conditions. The mechanical properties and crack propagation behaviors of sandstone specimens were analyzed. In addition, a new damage variable based on crack evolution was proposed. The experimental results showed that the strain-softening modulus of the sandstone specimens under triaxial loading and unloading compression conditions decreased with the increases in the loading rate. Meanwhile, the elastic modulus was only observed to undergo small changes. This study found that with the increases in the loading rates of axial stress, the deformation and strength levels of the sandstone specimens also increased. In addition, the crack initiation stress showed a linear increasing trend with the increases in the loading rates of axial stress. The peak crack volumetric strain displayed a slight increase with the loading rate of axial stress, which indicated that the larger the loading rate of axial stress on the sandstone specimens was, the smaller crack propagation strain levels at the peak stress levels would be. The crack propagation velocities were observed to be larger when the loading rates of axial stress were higher. Also, at the same loading rate of axial stress, the crack propagation velocity corresponding to the peak stress of the volumetric cracks was the largest, followed by radial cracks. The crack propagation velocity of the axial cracks was determined to be the smallest. In this study, a new crack damage variable based on crack volumetric strain was proposed. According to the evolution of the crack damage variables of the sandstone specimens, the following four stages of the failure process were obtained: original damage stage; elastic stage; linear damage stage; and accelerated damage stage. The results obtained in this research study provided an important scientific basis for the support of future designs and safety protection measures in underground mining operations.
The compression deformation and particle breakage of gangue filling materials are significantly affected by different particle size gradations. To study the mechanical behavior of mixed size gangue ...backfilling materials in-depth, a physical compression experiment of mixed size gangue was carried out by designing a scheme based on Talbot's theory and fractal theory was used to quantify the breakage degree of mixed size gangue particles. Then, a discrete element numerical simulation was used to study the particle breakage mechanism of mixed size gangue in the compaction process. The results show that under the same vertical load, the settlement decreases monotonically with the increase in the Talbot's exponent (n), and the filling effect is significantly enhanced. The particle size distribution of mixed size gangue sample after compression has extremely good fractal characteristics. The fractal dimension has superior linear function regression relationship with n and crushing ratio. The fractal dimension decreases with increasing n. and the crushing ratio declines with increasing fractal dimension. Large-particle-size gangue is mainly broken at the initial stage of loading, while the crushing ratio of small-particle-size gangue gradually increases after the compaction stage. Large-particle-size gangue is the main bearing structure of the strong force chain, thus forming a strong skeletal structure. In the process of axial loading, cracks are mainly distributed near the “force chain skeleton”, and the contact forces around the skeleton are the first to be broken. This phenomenon causes the breakage of gangue particles, the rearrangement of particle positions and greater subsidence to fill the pores.
Traditional cemented paste backfilling continues to face the shortcomings such as paste leakage, poor adaptability to geological structures and insufficient roof-contact. To solve the limitations, a ...novel L-shaped cemented paste backfilling (LCPB) technology was proposed in this study. It is to set L-shaped filling zones and partition zones in the goaf to perform interval and multiple filling. A mechanical model was established to calculate backfilling body strength, widths of L-shaped filling zones and partition zones and backfilled ratio and etc. The results of a case study showed that: (1) The LCPB mining has a high backfilled ratio, without prominent ground pressure. The maximum values of roof-to-floor convergence of the working face and roadway were 58 mm and 259 mm, respectively. It could effectively control the deformation of surrounding rock and achieve roadway retention. (2) When the floor strata were intact, the maximum floor damage depth was less than 4 m, and the floor near the fault was 10–12 m. The secondary lift height of the confined water was about 5 m near the fault. The LCPB mining allows for safety mining above a confined aquifer. (3) The maximum surface inclination and curvature were 1.75 mm/m and 0.06 mm/m
2
, respectively. The draw angle was 11.3°, and the subsidence factor was 0.085. The ground surface deformation was reduced to be less than that allowed in the first level of the building damage (inclination and curvature of 3 mm/m and 0.2 mm/m
2
, respectively).
Article Highlights
L-shaped interval cemented paste backfilling (LCPB) technology was proposed.
The critical parameters of LCPB were theoretically determined.
LCPB in ground control was verified through an engineering application.
It is important to study the mining technology under structures for raising the coal resources recovery ratio. Based on the geological and mining conditions, the top coal caving harmonic mining ...technique in thick coal seam beneath the earth dam was put forward and studied. The 5 factors such as the panel mining direction, panel size, panel location, panel mining sequertce and panel advance velocity were taken into account in this technique. The dam movement and deformation were predicted after the thick coal seam mining and the effects of mining on the dam were studied. By setting up the surveying stations on the dam, the movement and deformation of the dam were observed during mining. By taking some protective measures on the dam, the top coal caving mining technique in thick coal seam beneath the earth dam was carried out successfully. The study demonstrates that harmonic mining in thick coal seam is feasible under the dam. The safety of the earth dam after mining was ensured and the coal resources recovery ratio was improved.
The height of fractured zone (HFZ) at the high-intensity longwall mining panel plays a vital role in the safety analysis of coal mining under bodies of water. This paper described definitions of the ...high-intensity mining. The processes of overburden failure transfer (OFT) were analyzed, which were divided into the development stage and the termination stage. Through theoretical analysis, the limited suspension-distance and the limited overhanging distance were proposed to judge the damage of each stratum. Mechanical models of strata suspended integrity and overhanging stability were established. A theoretical method to predict the HFZ at the high-intensity longwall mining panel was put forward based on the processes of OFT. Taking a high-intensity longwall mining panel (No. 11915 panel) as an example, the theoretical method proposed, the engineering analogy and the empirical formulas in the Regulation were used to predict the HFZ. The results show that the theoretical result is consistent with the engineering analogies’ result and empirical formulas’ result. The rationality and reliability of the theoretical method proposed is verified.
The contradiction between efficient coal mining and arable land capacity enhancement in the coal–grain production overlapping area has constrained grain output and threatened food security. In this ...study, DInSAR was used to extract the mining subsidence areas (SAs). Multiple red-edged vegetation indices were introduced to explore the growth differences between winter wheat in the SAs and Check Areas (CKs). A crop health index (SACHI) was proposed to comprehensively evaluate the health of winter wheat in SAs. The results showed that: (1) Compared with the CKs, the onset of over wintering season (OWS), start of growing season (SOS), and end of growing season (EOS) of winter wheat lagged behind in the SAs. (2) The winter wheat growths were slower in the SAs and their decline rates were faster than that in the CKs. (3) The SACHI could effectively synthesize the information contained in each component and was highly correlated with them. (4) Mining subsidence had a significant impact on the winter wheat health in the length of growing season (LOS), while the impact was weakened during the OWS. Based on the multi-vegetation indices and the SACHI, the impact of mining subsidence on the winter wheat health can be effectively diagnosed and estimated.
In the ecologically fragile mining area of northwest China, high-intensity mining has seriously affected the aquifer and surface eco-environment. In order to better implement water-preserved mining ...in ecologically fragile areas, the aquifer failure characteristics should be first detected accurately; therefore, it is necessary to find a convenient and fast detection method. Based on the analysis of the basic principles and influencing factors of the magnetotelluric (MT) method, the feasibility of using the MT method to detect aquifer failure is verified by testing the mined area with MT detection and field borehole measurement. Subsequently, the failure characteristics of overburden and unconsolidated aquifers under high-intensity mining are studied by MT detection and physical simulation. By comparing the physical simulation with the field measurement from the aspects of the maximum surface subsidence, interval of periodic weighting and step cracks, the reliability of the height of the water flowing fracture zone and caving zone obtained from physical simulation is verified. The analysis from MT detection and physical simulation shows that the results of the two methods are in accord with each other, which further confirms that the MT method can be used to detect the failure of overburdened structures and aquifers. The penetrating fractures are the main channel for the downward seepage of water resources, which is caused by the “two-zone” of overburden model and located in the “dimple” shape in the apparent resistivity (AR) isogram. It can provide a reference and technical support for the corresponding new water-preserved mining technology and the construction of digital mines.
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