Jixiong Zhang

Impact law of the bulk ratio of backfilling body to overlying strata movement in fully mechanized backfilling mining

Fully mechanized backfilling mining technology with waste, fly ash, and loess, etc. provides advantages of safety and high efficiency to the extraction of coal under buildings, railways and water bodies. In this paper, the bulk ratios of backfilling bodies with different waste and fly ash mixture ratio was analyzed with MTS815.02 electro-hydraulic servo rock mechanical testing system and compacting device, the optimal mixture ratio of waste and fly ash was determined, and it proposed that the backfilling body should be firstly compacted after being backfilled into the goaf. With numerical simulation, the impacts of bulk ratio of waste and fly ash backfilling body to overlying strata movement law and surface subsidence controlling in backfilling mining were analyzed, and it figured out the bulk ratio of backfilling body that could ensure a reasonable range of surface subsidence. Finally, the engineering application confirmed that the strata movement controlling in fully mechanized backfilling mining was more effective, the surface buildings and facilities were not severely influenced. The above achievements could provide technical reference for the successful implementation of fully mechanized backfilling mining.

Test on mechanical properties of solid backfill materials

Abstract In this paper, characteristics that the overlying strata movement is controlled by solid backfill materials are illustrated in the coal mining with solid backfilling method. In addition, the mineral and chemical composition, density and moisture content of waste rock and fly ash are tested and analysed by physical–chemical treatment. By investigating the compaction deformation and time-dependence characteristics under different ratios of waste rock to fly ash, the optimal ratio of the mixture is obtained to achieve the smallest deformation, and results show that deformation mainly occurs in the initial period of loading. Combining the results of density test on site backfill materials, it indicates that the mass ratio of backfill materials to coal mining is 0·83 in order to ensure the effective of controlling the overlying strata in the coal mining with solid backfill method. The findings of the research provide references for the selection of solid backfill materials in coal mining.

Effect of Particle Size on the Energy Evolution of Crushed Waste Rock in Coal Mines

List of symbols U Total energy U Dissipated energy U Released elastic energy U Dissipated energy for particle breakage and extrusion U Dissipated energy for friction between the samples and the compaction device r Axial compaction stress ea Corresponding strain of the axial stress r eb Remnant strain after stress unloading from the axial stress r to zero k Coefficient of lateral pressure l Frictional coefficient between the waste rock and the chamber wall D Diameter of the compaction device H Loading height of the waste rock H1 Height of the steel chamber H2 Length of the dowel bar H3 Thickness of the loading platen H4 Distance between the top surface of the dowel bar and the steel chamber

Measurement and numerical analysis of water-conducting fractured zone in solid backfill mining under an aquifer: a case study in China

Solid backfill mining has been applied to excavate coal seams under aquifers in China; however, the control effects of the water-conducting fractured zone (WCFZ) require further study. Therefore, based on the mechanical properties of the compacted backfill materials, a method for simulating these materials has been proposed, and the compaction of backfill materials subject to the effects of overlying strata has been simulated. Boreholes were used in the test area to measure the height of the WCFZ in the CT101 panel of the Wugou Coal Mine in Suixi Town, Anhui Province. The results indicate that the numerical simulation is basically consistent with measured data, which verifies the feasibility of the simulation method. Moreover, the backfill materials were placed into the gob to restrict the movement of rock strata, which helps reduce the mining impact and the height of the WCFZ. The research results provide a basis for the design of backfill mining under aquifers.

Roadway Backfill Coal Mining to Preserve Surface Water in Western China

In China’s western eco-environmental area, water resources are very valuable. Longwall mining can cause these shallow water resources to leak, so most mines in this area use room-and pillar mining to prevent water inrush and protect water resources. However, over time, coal pillars can become unstable and collapse. To protect water resources and improve coal recovery, roadway backfill coal mining was proposed for the Ershike Coal Mine. The mechanical properties of backfill materials with different ratios of aeolian sand, fly ash, and Portland cement were studied in the laboratory to obtain an optimal ratio. Also, a 2-D physical simulation model was established to explore the development of mining-induced fractures and to conduct a stability analysis of aquiclude strata. The results can be used to guide coal mining in the study area and to protect local water resources.抽象中国西部半干旱区水资源宝贵。长壁回采会引起浅部水资源渗漏,因此西部矿区多采用房柱式开采防止煤矿突水和保护水资源。为保护水资源和提高煤炭回采率,在Ershike矿提出掘巷充填回采法。采用室内试验研究了风积沙、粉煤灰和硅酸盐水泥不同配比充填材料的力学性质,以获得最优配比。同时,利用二维物理模拟模型研究了采矿裂隙发育特征和隔水层稳定性。研究结果可指导区内煤炭开采 和水资源保护。ZusammenfassungIn Westchinas Naturschutzreservat sind die Wasserressourcen sehr kostbar. Der Streckenbergbau kann zur Versickerung dieser wertvollen Wasserressourcen führen. Daher verwenden die meisten Bergwerke in diesem Gebiet die Pfeilerbruchbauweise, um das Eindringen des Wassers zu verhindern und die Wasserressourcen zu schonen. Mit der Zeit können die Pfeiler allerdings instabil werden und zusammenbrechen. Für die Ershike Kohlemine wurde die Rückverfüllung der Strecken empfohlen, um die Wasserressourcen zu schonen und die Kohleausbeute zu erhöhen. Zur Bestimmung der optimalen Zusammensetzung des Versatzmaterials, bestehend aus unterschiedlichen Anteilen von äolischem Sand, Flugasche und Portlandzement, wurden die mechanischen Eigenschaften im Labor untersucht. Zusätzlich wurde ein physikalisches zweidimensionales Modell entwickelt, um die bergbauinduzierten Brüche zu untersuchen und eine Festigkeitsanalyse der Grundwasserstauer durchzuführen. Die Ergebnisse können genutzt werden, um den Kohleabbau im Untersuchungsgebiet zu begleiten und lokale Wasserressourcen zu schützen.ResumenEn el área eco-ambiental occidental de China, los recursos hídricos son muy valiosos. La minería puede hacer que estos recursos de agua poco profundos tengan fugas, por lo que la mayoría de las minas en esta área usan la minería de cuartos y pilares para prevenir la entrada de agua y proteger los recursos hídricos. Sin embargo, con el tiempo los pilares de carbón pueden volverse inestable y colapsar. Para proteger los recursos de agua y mejorar la recuperación de carbón, se propuso minería de carbón de relleno del camino para la mina de carbón de Ershike. Se obtuvieron las propiedades mecánicas de los materiales de relleno con diferentes relaciones de arena eólica, cenizas y cemento Portland para obtener una relación óptima. También, se estableció un modelo físico de simulación en 2-D para explorar el desarrollo de las fracturas inducidas por la minería y permitir un análisis de estabilidad del estrato acuicludo. Los resultados pueden ser usados para guiar la minería de carbón en el área de estudio para proteger los recursos locales de agua.

A case study of mining-induced impacts on the stability of multi-tunnels with the backfill mining method and controlling strategies

Deep mining practices are jeopardized by the recurrent instability and failure of roadways/multi-tunnels. This paper describes a case study of the mining-induced impacts on the stability and control strategy of overlying multi-tunnels with backfill mining in the Ping Dingshan No. 10 Coal Mine in Henan Province, China. To reveal the dynamic impacts of coal mining on the stability of overlying multi-tunnels, particularly in the process of mining cycle and after the overlying strata long-term stability period, a 3D finite element model was applied to explore the effect of longwall panel width, advancing distance, and backfill material’s compaction ratio (BMCR) on the multi-tunnels’ deformation characteristics. The results obtained demonstrate that failure and deformation of the overlying multi-tunnels become more pronounced with the increased longwall panel width and advancing distance, as well as with BMCR reduction. The ranking of deformation degree in the overlying multi-tunnels is as follows: main haulage roadway > auxiliary haulage roadway > main inclined shaft > rock crosscut > auxiliary inclined shaft. Using a 2D physical simulation experiment, a comprehensive analysis method and engineering design concept for the stability control of overlying multi-tunnels with backfill mining are put forward based on further research of the deformation characteristics of multi-tunnels using caving and backfilling method. The results obtained are instrumental to the stability control of overlying tunnels in deep mining practices with similar conditions.

Influence of pH values on WO3 nanomaterials during hydrothermal synthesis and its gas-sensing properties

Abstract As a promising gas-sensing material, tungsten tri-oxide with a wide band gap has attracted much attention. However, the preparation of tungsten tri-oxide nanomaterials in alkaline solution faces difficulties because of the weak solubility of the tungsten source. Here, the influence of pH values on the final products was investigated in detail. The results showed that pH value played no role in the phase for the final product. However, it had an obvious impact on the morphology evolution. Gas-sensing properties showed that the sensitivity increased with the increase of synthesised time because of improved crystallinity. Moreover, the sensitivity of the product synthesised in an alkaline environment was obviously higher than that of the product synthesised in an acid environment.

Mechanical Analysis of Roof Subsidence Based on Rheological Properties of Solid Backfill Materials

To study the influence of the rheological properties of backfill materials on strata movement during solid backfill mining, Poyting-Thomson model was selected as the rheological model for the backfill materials based on their experimentally derived rheological properties. By regarding the roof as a thin elastic plate, a rheological mechanical model of the roof when using solid backfill mining, was established. According to the elastic-viscoelastic correspondence principle, the deflection of the roof at different times was obtained by use of the energy method. By taking the 7203W backfill mining panel of a coalmine in Zhaizhen town as an example, the subsidence of the roof over time was calculated. Results showed that the maximum subsidence was 205 mm, which was close to that measured in situ. Meanwhile, the observation of boreholes drilled into the roof evinced its integrity. Therefore, these results can provide a theoretical basis for predicting strata movement and surface subsidence during solid backfill mining.

Pore pressure evolution and mass loss of broken gangue during the seepage

Broken gangue consists of different particles, and it has more complicated seepage characteristics than intact rock sample. Using the self-designed instrument, the permeability, mass loss and pore pressure of crushed gangue during the seepage are tested. The result shows that permeability parameter k of crushed rock has a polynomial relationship with effective stress σ′ in inverse proportion, and permeability parameter β of crushed gangue has power exponent relationship with effective stress σ′ increasing in direct proportion. The particle size of 8.0–10.0 mm has a good support effect. The inner pressure of crushed rock is mostly linear distribution along the tube wall. After the seepage, mass loss of broken gangue mainly increases with large particle size out of proportion.

Multi-fractal characteristics of particle size distribution of granular backfilling materials under different loads

Abstract This study is focused on the inhomogeneity and local heterogeneity of the particle size distributions (PSD) of granular backfilling materials (eolian sands and loess) from western mines of China under overburden strata loads. The multi-fractal spectrum and variations in corresponding parameters of PSD of granular backfilling materials were obtained under different loads using a laser particle size analyzer and an environmental scanning electron microscope (ESEM). The results indicated that the load had negligible effects on the multi-fractal characteristics of PSD of eolian sand. There were no significant variations in the capacity dimension D(0), the information entropy dimension D(1) and the bandwidth of the multi-fractal spectra (Δα) as a function of the load. In contrast, the load significantly affected the multi-fractal characteristics of the PSD of loess, and D(0), D(1) and Δα increased and then decreased (maximized at 2 MPa) as the load increased. Furthermore, there was a correlation between structural morphology parameters and multi-fractal parameters in the particle breakage process, which demonstrated that D(0), D(1) and Δα of PSD of granular backfilling materials could effectively reflect the particle breakage and the change of structural morphology parameters of backfilling materials under different loads.