| As a green and ecological coal mining technology,backfill mining utilizes solid waste to displace coal resources,thereby controlling safety,social,and ecological risks associated with resource extraction from the source.It represents an innovative strategy for environmentally friendly coal mining.Effective implementation of backfill mining can reduce surface subsidence,preserve farmland and avoid relocation of villages,greatly minimizing the impact of mining on local communities.The paste filling mining has not been carried out in Huainan mining area.Compared with other mining areas in China,the filling mining conditions of extremely thick loose layer,extremely weak roof,large mining depth and more old goaf residue are also very rare.These conditions will inevitably affect the law of overburden movement and surface settlement in filling mining,so it is urgent to carry out in-depth research to provide reference for mining safety.Taking the 1241(3)backfill mining working face in the Huainan mining area as a case study,this paper combines theoretical analysis,numerical simulation,and field experiments to observe and analyze the strata movement and surface deformation during deep backfill mining with paste material.The main achievements of this study are as follows:(1)Through numerical simulation experiments,the strata movement and surface deformation during deep backfill mining with paste material were investigated.The experimental results showed that:1)During the advancement of the working face,the shape of the roof strata gradually transitioned from a "cone" shape to a "saddle" shape with greater subsidence in the middle of the goaf and smaller subsidence on the sides.2)The bedrock layer was significantly affected by the mining activities,and the subsidence curve of other rock layers,except near the roof,exhibited a sharp "cone" shape.3)In the process of filling mining activities,the thick loose layer has a certain easing effect on the surface settlement.Therefore,there is no drastic wave settlement or stepped settlement on the surface,and the settlement curve is close to the moderate parabola,with a small subsidence amount and a large influence range.4)The backfill material experienced pressure from the overlying strata during mining.The effective active space of the rock layers was small,leading to the absence of distinct "upper three zones" in the overlying strata above the goaf.Instead,there was a overall bending deformation where the bedrock layer and the loose layer remained closely attached and deformed together throughout the mining process.5)According to the experiment of several controllable factors affecting the effect of surface subsidence control in the actual production,it is found that the maximum surface subsidence value is approximately linearly negative correlated with the filling rate,and is proportional to the mining thickness and mining space within a certain range.The normalization of the three factors shows that the filling rate is the key factor to control the surface subsidence,and the influence of mining space in the early stage is also strong,and the influence of mining thickness is stable.(2)Based on the fundamental theory of elastic foundation beams,an elastic mechanics model for the roof strata of a single working face in deep coal mines with paste backfill mining was established and solved.The following findings were obtained:1)Based on the bending deformation characteristics of the roof strata in paste backfill mining,an elastic mechanics model for the roof strata in deep coal mines was established.The equation for calculating the deflection of the roof strata in the controlled roof zone and backfill zone was derived,and subsequently,the deflection equation of the roof strata with respect to the distance from the coal wall was solved.2)By using the method of controlling variables,the variation trend of the roof strata’s subsidence under the influence of single factors was analyzed.The thickness of the roof strata affects its flexural stiffness,which in turn affects the subsidence rate of the roof strata in the controlled roof zone.However,it has little influence on the stable subsidence value of the roof strata in the backfill zone.The overlying load and filling rate have a significant impact on the maximum subsidence of the roof strata.In practical production,the depth of the coal seam cannot be controlled,leading to the immutability of the overlying strata load.Therefore,the subsidence of the roof strata can be reduced by increasing the filling rate.(3)This study investigated the characteristics of surface deformation in deep coal mining with backfilling,focusing on the residual deformation influenced by the old goaf.The following findings were obtained:1)Under the influence of the old goaf,the maximum subsidence value of the working face is 145 mm,which is far less than the surface subsidence value of conventional mining under the geological mining condition.The horizontal movement of the surface exhibited a similar pattern to conventional mining-induced subsidence,with the maximum horizontal displacement of 62 mm occurring at a distance of approximately 23-26 m outside the goaf area.2)The observation points with the greatest influence from residual deformation were distributed on the side of the heading line and in the uphill direction of the trend line.The point with the largest residual deformation was identified as MS42,with a deformation value of 50 mm.3)After removing the influence of residual subsidence from the measurements at each observation point,the maximum subsidence was determined to be 123 mm.The subsidence data at both ends of the observation line returned to a more normal trend,indicating significant convergence of the subsidence basin.4)Using the measured data from observation points with residual subsidence removed,the probabilistic integration method was applied to invert the parameters for predicting the subsidence at the 1241(3)backfill mining working face.The inverted subsidence values showed a high degree of agreement with the measured results,and the subsidence boundary closely matched the actual boundary,demonstrating the reliability of the inversion.Figure [30] Table [11] Reference [90]... |
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