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a b s t r a c tBased on the loose medium flow field theory, the loose top-coal drawing law of longwall top-coal caving (LTCC) mining technology is studied by using self-developed three-dimensional (3D) test device. The loose top-coal drawing test with shields and the controlled test without shields are performed in the condition without any boundary effect. Test results show that shields will cause reduction in drawing volume of coal in the LTCC mining. The deflection phenomenon of drawing body is also observed in the controlled test, which is verified that the deflection of drawing body is caused by shield. It is found that the deflection angle decreases with increasing caving height, with the maximum value of a tail and the minimum value of 0. In addition, the formula to calculate the drawing volume is proposed subsequently. The deflection of drawing body is numerically simulated using particle flow code PFC 3D and the proposed formula to calculate drawing volume in LTCC is also verified.

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a b s t r a c tSince longwall mining causes subsidence through the overlying strata to the ground surface, the surface water and groundwater above the longwall panels may be affected and drained into the lower levels. Therefore, loss or interruption of streams and overburden aquifers is a common concern in coal industry. This paper analyzed the potential effects of longwall mining on subsurface water system in shallow coal seam. In order to monitor different water level fluctuations throughout the mining period, three water wells were drilled down to the proposed deformation zone above the longwall panel. A GGU-SS-FLOW3D model was used to predict water table contours for the periods of pre-and post-mining conditions. The field data from the three water wells were utilized to calibrate the model. The field test and numerical model can help to better understand the dewatering of shallow aquifers and surface waters related to ground subsidence from longwall mining in shallow coal seam.

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The microstructure changes brought by the addition of Nd element to AM60 magnesium alloy were studied, the precipitating phases were identified and their influences on the mechanical properties of alloys were investigated. Results show that Nd addition makes the refinement of microstructure of the AM60 alloy, and decreases the size of Mg17Al12 phase. Nd element takes a priority to react with Al element over Mg, Mn and Zn forming binary phase Al11Nd3 with high melting point. Certain content of Nd can increase tensile strength, yield strength and elongation of the alloy. But with too much addition, Nd would combine with more Al in matrix and decrease strengthening effect because Al11Nd3 phase would become coarsening. The mechanical property tests indicate that AM60-0.9Nd alloy has the best properties. Maximum tensile strength, maximum yield strength, maximum elongation are 230 MPa, 127 MPa and 14% respectively, increased by 28%, 48% and 250% respectively.