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Longwall extraction of coal seam disturbs the whole overburden strata, from the coal seam to the surface, and forms a subsidence basin. This paper investigated the mechanism of the overburden strata bending deformation, the alluvium mechanical parameters, and their effect on surface subsidence by the theoretical analysis and numerical simulation analysis. The dynamic processes of overburden failure and surface subsidence due to longwall mining was analyzed by a novel two-dimensional trapezoidal-area method. A “π-shaped” model was first developed to reveal that surface subsidence consists of the overburden strata bending deformation and the subsidence of the alluvium. The process and mechanism of the overburden strata bending transfer were analyzed, and two mechanical models of the strata bending deformation were established, i.e., the strata suspended bending model and the strata overhanging bending model. The maximum subsidence equation of the overburden strata bending basin was derived based on the theoretical analysis. Also, the effect of the alluvium mechanical parameters on the surface subsidence was investigated by numerical simulation analysis. The rationalities of the numerical simulation were validated by the field measurements. The results show that surface subsidence increases logarithmically during increased alluvium thickness and decreases exponentially and logarithmically during increased internal friction angles and increased cohesions, respectively.

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A simple process of thermal oxidation and self-assembly modification was developed to fabricate a stable superhydrophobic film with controllable adhesion on titanium surface. Pure titanium plate was first heat treated in atmospheric environment at 900 °C, 1000 °C and 1100 °C respectively for a certain time, then air cooled. The subsequent air-cooling process separated the flaky yellow oxide layer formed on titanium plate during the oxidation from the substrate and a rough titanium oxide surface with micrometer and nanometer-scale hierarchical structures was obtained. The following immersion process in N-octadecyltrichlorosilane solution endowed the surface with excellent water repellence, raised its contact angle up to 166° and reduced its slide angle as low as 2°. What's more, by controlling heat temperature and time, the surface's superhydrophobicity switched from sticky state to sliding state. Field-emission scanning electron microscopy (FE-SEM) and contact angle measurement were used to characterize the morphological features and wettability of the as-prepared surface respectively. Immersion test in corrosive liquids and abrasion test with sandpaper have a further exhibition of its chemical stability and mechanical durability. The result is meaningful to a wider range of future applications of superhydrophobic titanium surface in industry and real life.

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 &ldquo, two-zone&rdquo, of overburden model and located in the &ldquo, dimple&rdquo, 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.

Ti and its alloys,due to their good stability and high strength-to-density ratio,have been widely used in many industry fields,such as aviation,navigation,biomedical devices,etc.It is quite necessary to improve their performance against corrosion of water pollution or other corrosive mediums in these fields.The process of thermal oxidation is an effective way to enhance their corrosion resistance while high-temperature oxidation is usually thought to have detrimental effects.However, the porous structure caused by high-temperature oxidation is found to be beneficial for preparation of superhydrophobic surface,which has gotten extensive application in improvement of metals' antcorrosion ability.In this study,a rough surface with hierarchical micro- and nano-structures was formed on Ti by a heat treatment process in atmospheric environment at 1000℃for 1 h.The following air-cooling process separated the flaky yellow oxide layer formed on Ti plate during the oxidation from the substrate and a grey porous substrate(TO) was obtained.Furthermore,TO was modified with n-octadecyltrichlorosilane(OTS),leading to the formation of superhydrophobic Ti surface(TO-OTS).The TO-OTS film exhibited a static contact angle of 166.0°and a rolling angle of 2.0°for 5μL water droplets.The as-prepared film was characterized by XRD,FE-SEM,XPS and contact angle measurements.The results indicated that dual-scale roughness leaved by thermal oxidation endowed TO-OTS with excellent non-sticking superhydrophobicity and durability,even for some corrosive liquids including salt solution and acidic and alkali solutions at different pH values. By means of immersion test,TO-OTS displayed great non corrodibility against HF solution,with a protective mirror-like air film formed above it.Moreover,based on potentiodynamic polarization measurement in 3.5%NaCl solution,the corrosion resistance of TO-OTS was proved to have a significant enhancement with a protection efficiency of 99.1%.This is a facile method for preparation of large-scale or complex shaped superhydrophobic surfaces without requirement of expensive instrument, which may provide an effective protection for Ti under harsh environment.