The shale in Doushantuo Formation is the main source rock of the Ediacaran in Sichuan Basin and the major hydrocarbon source layer of the ancient marine strata for natural gas exploration in recent years. Forty-six samples were collected from two outcrops(Baibaoxi and Shiping)in Chengkou county in northeastern Sichuan Basin.We analyzed the change of the sedimentary environment of the Member Ⅱ and Ⅳ of Doushantuo Formation in terms of their organic geochemical characteristics(total organic carbon, rock pyrolysis, kerogen carbon isotopes)and element geochemical characteristics(major elements, trace elements and rare earth elements).Results show that the shale of Doushantuo Formation in northeastern Sichuan Basin exhibit a high abundance of organic matter, with TOC content ranging from 0.19 % to 20.38 % (mean value is 4.76 %). The dominant type of organic matter is type Ⅰ kerogen, and it has reached over-maturity stage. High δEu anomalies and abnormally richness in V, Mn, Mo, Ba and U elements of the black shale revealed strong hydrothermal action during this period. The distribution pattern of rare earth elements and various redox indexes indicated that the redox fluctuates repeatedly under the conditions of anaerobic-anoxic-sulfidic environment during the depositional period of the Member Ⅱ. The water environment of Member Ⅳ changed from anoxic to anaerobic-sulfidic environment. In general, the water connectivity of the basin is strong, the depositional rate is relative high. The nutrients carried by upwelling from hydrothermal sources proliferate productivity, which promotes the formation of organic shale.

Natural fractures are important storage spaces and seepage channels in tight carbonate reservoirs. It is therefore of practical significance to quantitatively predicting their development and distribution patterns and revealing the dominant geological factors that control the development of gas reservoirs. This study looks at the fractures in the tight carbonate reservoir of Dengying Formation in Gaoshiti block of Leshan-Longnusi ancient uplift in the central Sichuan Basin. Based on the characterization of fracture parameters, we established a calculation model of stress field-energy-fracture parameters, and carried out quantitative prediction of fracture development and distribution patterns by combining multi-phase fracture superimposition algorithms. We then analyzed the influence of lithology, faults, and structural morphology on fracture development. The results show that: (1)The fractures in Dengying Formation of Gaoshiti block are mainly tension-shear fractures, high-angle fractures, and semi-filled fractures. The preferential fracture strike is NW-SE and near N-S directions. The fracture density is between 0 and 2 fractures per meter, and the high-value areas are mainly distributed in the fault zones and central regions; (2)There is a negative exponential power relationship between the length and density of natural fractures in the Gaoshiti block. Fracture development exhibits interlayer differences: The limestone reservoir has a high degree of fracture development, and mudstone has a blocking effect on fracture propagation; (3)Fracture development scale and occurrence are significantly affected by faults and folds: fracture around faults shows high density, large aperture and short length. Shear fractures are nearly parallel or at a low angle to strike-slip faults, and tensile fractures are at a high angle to the main strike-slip faults; folds mainly affect fracture aperture through structural curvature, with larger fracture apertures in high-degree deformation structural positions, and smaller values in the wings. The results could provide references for efficient exploration and profitable development of gas reservoirs in the study area and other regions with similar geological conditions.

This study conducted the CO₂-PTF coal experiment to further reveal the fracturing transformation mechanism of CO₂ phase transition fracturing(CO₂-PTF)coal. According to the CT scanning and 3D fracture reconstruction, we analyzed the fracture structure parameters of coal before and after CO₂-PTF, and clarified the evolution characteristics of the three-dimensional fracture structure of coal induced by CO₂-PTF. The research results indicated that after CO₂-PTF, the total number of fractures in the coal sample decreased, while the total volume and surface area of fractures increased. The CO₂-PTF generated fracture expansion and transformation effects where the small-scale fractures were expanded and transformed into larger scale fractures under the CO₂-PTF pressure. The number, volume, and surface area of fractures of less than 1 000 μm in length were significantly reduced, while the volume and surface area of fractures of longer than 1 000 μm in length were significantly increased. The expansion and connection between fractures caused a decrease in their quantity. CO₂-PTF improves the connectivity of the three-dimensional fracture in coal and is conducive to gas migration and production. This study offers new insights into and evaluation method for the effect of CO₂-PTF, and could provide references for the research on fracture evolution characteristics in other unconventional natural gas reservoirs and their modifications.

The high geothermal environments encountered in deep mineral mining induce thermal damage to rocks, which can trigger geotechnical disasters in deep engineering projects. Therefore, exploring the degradation characteristics of rock mechanical properties and the damage evolution laws after high-temperature exposure is of significant importance for rock engineering in deep high-geothermal environments. By subjecting granite to the temperature range from ambient to 1200 ℃ and conducting macro-microscopic studies using optical microscopy, the degradation characteristics of Young's modulus and compressive strength in granite samples post various high-temperature treatments were investigated. Additionally, an analysis was performed on the internal cracks and damage evolution in thermally damaged granite from a microscopic perspective. The experimental results demonstrate that high-temperature treatments significantly reduce the mechanical properties of granite. The granite's compressive strength and Young's modulus decrease with increasing treatment temperatures, and the extent of crack development increases with temperature. The mechanic cal properties of granite are highly correlated with the development of internal crack structures. There is a power function relationship between the crack density and compressive strength in granite after different temperature treatments, indicating that crack density can effectively reflect the extent of thermal damage in granite.

In light of the significant presence of liquefiable sandy silt layers in the foundation of the airfield area at the Beijing Daxing airport, this study employed a low-energy, small spacing, and low blow count dynamic compaction method to treat it.To assess the compaction effects and determin the parameters of the compaction process, two energy levels of 1 000 kN·m and 2 000 kN·m were selected, with each energy level tested at 4, 6, 8, 10, and 12 blow counts. Additionally, the effect of the surface frozen soil layer on compaction was investigated using 1 000 kN·m energy level with 4, 6, and 8 blow counts. The full depth standard penetration, surface wave and dry density tests were carried out in the dynamic compaction test area. The experimental results revealed that the sandy silt soil foundation exhibited increased compaction, propagation wave velocity, and enhanced liquefaction resistance after dynamic compaction. Optimal blow counts were determined as 10 and 8 for energy levels of 1 000 kN·m and 2 000 kN·m, the corresponding dynamic consolidation depth is 4.5m and 5.5m, and the eliminating liquefaction depth is 4.3m and 5.3m, respectively. Besides, the standard penetration test requires a minimum of 10 and 12 blows in the depth range of 4.5 m and 5.5 m for energy levels of 1 000 kN·m and 2 000 kN·m. At the optimal blow counts, the dry density of the surface layer of the original foundation should not be less than 1.45 g/cm³. The experimental results suggest that, for foundation treatment in the runway area, the dynamic compaction level of 2 000 kN·m is suitable, and 1 000 kN·m dynamic compaction level is used for foundation treatment in the apron and taxiway area.

The use of prestressing anchor active support technology in tunnel engineering is becoming morecommon.However, the support characteristics and mechanism of action have not been fully understood for shallow, large-span rocky tunnels.In order to investigate the bearing characteristics of the surrounding rock under the prestressed anchor support system, a concealed excavation station of Qingdao Metro Line 6 was used as the engineering background, and based on the similarity principle of formulating experimental materials for stratum and support structure modelling, the bearing characteristics of the anchors under the prestressed anchor and ordinary anchor support were investigated by hydraulic loading tests.The results indicate that: ① The interaction between prestressed anchors and the surrounding rock creates a load-bearing anchor solid that can effectively support most of the overlying loads.The application of prestressed anchors during the overburden loading process increased the warning load value of tunnel instability damage by 42.8% and the ultimate load value by 41.2%.② The overburden loading process involved the prestressing anchors going through the tight anchorage load holding stage and the de-anchorage unloading stage.Simultaneously, the lining underwent the strain accumulation stage, strain surge stage, and strain release stage during the overlay loading process.③ The prestressed anchor under active support has better force synergy with the rock body than an ordinary anchor, without the axial force mutation phenomenon.This allows the support performance of the anchor to be fully utilized.Additionally, the prestressed active support effectively inhibits the development of fissures and significantly improves the overall stability of the tunnel.

Aiming at the corrosion problem of steel bars in concrete in subtropical marine environment, the full immersion corrosion experiments of reinforced concrete specimens with different strength grades and rust inhibitor contents were carried out by simulating the subtropical marine environment.The macroscopic indexes such as chloride ion content were tested by electrochemical non-destructive testing, and the experimental results were verified by microscopic detection methods.The corrosion degradation patterns of reinforced concrete was analyzed.The results show that the improvement of concrete strength grade and the increase of rust inhibitor content can significantly improve the corrosion resistance of reinforced concrete.Among them, the corrosion resistance of C30 concrete is the worst.At 120 d, the corrosion current density is 0.118 μA/cm², the polarization resistance is 220 kΩ cm², the concrete resistance is 87.3 kΩ cm², and the transfer resistance of the steel-concrete interface area is 77.3 kΩ cm², reaching the passivation state.When the concrete strength grade is increased to C50, the corrosion current density is reduced by 58.47%, the polarization resistance is increased by 3.82 times, and the concrete resistance is increased by 44.56%;when the amount of rust inhibitors is 6 kg/m3, the corrosion current density is reduced by 47.45%, the polarization resistance is increased by 2.81 times, and the transfer resistance at the reinforcement-concrete interface is increased by 72.43%.

Improving the positioning accuracy of underground personnel can not only strengthen mine safety monitoring, but also increase the speed of rescue, thus ensuring the life safety of underground personnel to the maximum extent.This paper proposes a positioning model based on IPSO-LSTM for position prediction of underground moving targets in response to the problem of existing ranging algorithms which are affected by the on-site environment, resulting in insufficient positioning accuracy.This article uses LSTM to build a fingerprint positioning model.It collects distance information through the UWB wireless module to build a distance-position fingerprint relationship database, which is used to train the PSO-LSTM model.Then we use the trained model to predict target trajectories.We compared four improvement strategies on PSO including random initialization of population position by chaotic mapping, nonlinear inertia weight reduction and fitness function optimization.Experiments show that the improved PSO optimization algorithm in this paper exhibit fast convergence speed and good robustness.In order to verify the positioning effect of IPSO-LSTM, we compared the IPSO-LSTM model with the Chan algorithm, PSO-LSTM model, LSTM neural network, SSA-LSTM model and GWO-LSTM.The average positioning error is used as the evaluation index.The results show that the average positioning error of the IPSO-LSTM positioning model proposed in this study is 30mm, which is 76% higher than the traditional Chan algorithm, 49% higher than the LSTM, and 24% higher than the PSO-LSTM model.In order to reduce large local errors, we used median filtering to process input information, further improving positioning accuracy.This study offers references for improving the accuracy and stability of the existing underground moving target positioning system.

To reduce the pollution of the roadway environment and the damage caused by the personnel and equipment by the dust escaping from the fully mechanized driving face, a chemical and environmentally friendly dust suppressant with strong wettability and strong adhesion was developed based on the engineering background of the west-wing track roadway of Jining Jinqiao coal mine, and inhalable dust as the research object, with surfactants as the key skeleton and inorganic salts and polymer adhesives as auxiliary materials.The results of field verification show that the chemical dust suppressant has a better ability to lithological particles and can effectively reduce the concentration of respirable dust in the roadway.

As the core unit of backfill mining method, the strength of backfill is an important indicator to ensure safe mining. Na-based bentonite features a high methylene blue adsorption capacity and green compressive strength, making it a high-quality additive for preparing filling materials. However, there are few studies probing into the relationship between the dosage and the strength of the filling materials. This paper analyzes the changes in shear wave velocity, dominant frequency amplitude, amplitude attenuation coefficient, and waveform fractal dimension of filling materials with different Na-based bentonite dosages at different ages through ultrasonic testing technology and uniaxial compression tests. Combined with sensitivity analysis, we selected the most sensitive acoustic parameters to changes in compressive strength. Furthermore, this study establishes a strength prediction model for backfill with different Na-bentonite contents and combining significance testing and comparative analysis. The research findings can serve as a valuable reference for theoretical research and engineering applications related to predicting the uniaxial compressive strength of backfill materials.

The evolution of fractures in mining overburden plays a pivotal role in interlayer gas migration. Therefore, a comprehensive study of crack development and distribution improve the efficiency of gas extraction. This study the west 2107 fully mechanized mining face in Weijia Mine of Gansu Province as the engineering background, Specifically, this study established numerical models of different mining heights by using the UDEC simulation software, and analyzed the relationship between the evolution of near-field fractures in the overburden of the working face and different mining based on fractal geometry theory. The optimal working face height for gas extraction was determined and validated through theoretical empirical formulas, field observations of overburden fractures, and gas extraction results. The results show that the total number of mining fractures increases with the increase of mining height, but the amplitude of increase is different at different stages, and the overburden fractures continue to develop in an "umbrella" shape around the overburden. The near-field fractures of the overburden rock at different mining heights have undergone three stages: generation, expansion and penetration, and compaction stability. Increasing mining height, smaller compaction zones. When the mining height is 4 m, the development density and range of roof fractures at 10 m and 40 m are significantly higher than those in other areas, which is consistent with the optimal position of the collaborative extraction roadway with high and low roadways.

This study aims to address existing problems of complex stress conditions and difficulties in retaining roadway so as to achieve long-term stability of roadway surrounding rock in gob-side entry in thin coal seam. Specifically, we investigated the 4301 working face of Liangshuijing Coal Mine in Huisen Coal Industry of Shaanxi Province through theoretical analysis, numerical simulation and engineering practice, with an aim to study the failure characteristics and control countermeasures of surrounding rock of gob-side entry retaining in shallow buried "triple hard" thin coal seam, and analyse the influence of structural parameters of roadside support on roadway stability. The results show that 1)maintaining the roadway through roadside filling body requires sufficient support strength and appropriate shrinkage to the roof and ensuring the overall stability of the roadway; 2)the mechanical behaviour of high water filling material under uniaxial compression can be divided into four stages: "uniform compaction, elastic deformation, dynamic instability and deterioration failure". The numerical simulation results show that in increasing the width of the filling body, the maximum stress first increases, then decreases and then increases, and a stable bearing stress core appears at 1.6 m. Theoretical calculation shows that the optimal height of roof cutting is 10.7 m, and it offers the roof cutting scheme and parameters of shaped blasting. Engineering practice shows that there is no large deformation and no obvious stress concentration in the 60 m range behind the working face. The surrounding rock exhibits good overall control effect and stable structure, and the effect of retaining roadway meets the design requirements.

Sprayed fireproofing materials in underground coal mine roadways are limited due to their poor adhesion, easy-to-crack, easy-to-fall off and poor sealing effect. This study therefore develops a fireproofing spraying material with fly ash as aggregate, ordinary silicate cement, sulphur-aluminate cement and gypsum as base material, and re-dispersible latex powder(VAE)as additive. Specifically, we conducted the uniaxial compressive strength test and used coal rock multiphase multi-field triaxial dynamic seepage experimental system, and scanning electron microscopy to study the effects of dispersible latex powder on the adhesive, cementation, mechanical, and blocking properties of the spray material. The results show that adding dispersible latex powder could promote the formation of filamentary bonding bridges in the hydration product, and realize the riveting and bridging of the binder bridges with the hydration products to form a dense network structure. This improves the cracking resistance of the spray material and enhances the material's adhesion, sealing and cementing properties when combined with coal. Adding 1 % VAE spraying material can fully encapsulate the coal body, forming a dense coating on the surface of the coal body, effectively isolating the air from contact with the coal body, thus preventing spontaneous combustion of coal. The proposed materials are useful in preventing spontaneous combustion of coal at the top of the roadway.

Coal production enterprises at present are facing immediate urgency to reduce their high carbon emissions so as to meet the "dual carbon" targets. This study therefore analyzed their potential in carbon emission reduction from the perspective of their coal products, mining processes and emission types. Specifically, this study proposed pathways for 1)upgrading coal production equipments, including the application of advanced clean technologies, upgrading and retrofitting production equipments, and implementing energy efficiency management strategies; 2)technology updates for coal exploration, mining, beneficiation and monitoring; 3)upgrading new energy vehicles and intelligent platforms for logistics management, and improving energy-consuming equipments for personnel in mining areas, all targeting at the major factors causing high carbon emissions; 4)upgrading coal and gas co-capture technologies and carbon sequestration methods during coal mining and beneficiation processes, based on which specific suggestions are offered for coal production enterprises. A comprehensive pathway for carbon emission reduction is thus constructed for coal production enterprises to achieve carbon peak and carbon neutrality.

Multistage fracturing is a commonly-used method to improve gas production in tight hydrocarbon reservoirs. Stress shadowing effect among multi-fractures is crucial in effectively connecting the pre-existing natural fracture of reservoir and forming a complex fracture network that facilitates gas flow. Challenges remain in accurately characterizing the fracture structure and propogation patterns of naturally fractured reservoirs. In this study, we adopt an adaptive finite-discrete element method to simulate the multistage fracturing of a naturally fractured reservoir by improving the mesh auto-refinement and identification of multiple fracture propagation. The numerical model covers interactions among hydraulic fractures, pre-existing fractures, and microscale pores, while integrates the nonlinear Carter leak-off criterion to describe fluid leak-off and hydromechanical coupling effects during multistage fracturing. We introduce the proppant transport equation for idealised parallel plate flow in fractures, and Darcy's law is adopted to analyse the seepage flow in the fracture network and determine gas recovery. We then compare the fracture network and consequent fluid flow induced by the hydrofracturing of unfractured and naturally fractured models to assess the influence of pre-existing fractures on multistage fracturing behaviour and gas production. This study provides a new approach to determine and optimize fracturing cluster spacing in tight gas reservoirs.