Study On The Law Of Surface Deformation And Evolution Of Overlying Strata Movement Characteristics Under Repeated Mining

Most of the coal seams in the Huainan mining area are single seams,and most of the working faces are the first mining.Researches on the laws of surface movement and deformation during the first mining have gradually become mature,but there are relatively few researches on the surface deformation,evolution characteristics of overlying strata displacement and stress under repeated mining.The surface deformation of repeated mining is more severe than the initial mining.Studying the development law of cracks generated under repeated mining conditions can enrich the surface deformation law of repeated mining in Huainan mining area;study the design of mining width and thickness of working face to achieve reducing the violent degree of overlying strata movement has certain reference significance for the size design of repeated mining face under similar geological mining conditions.Combined with the geological and mining conditions and the surface hydrological environment of the 11123 working face,a repeated mining surface movement and deformation observatory was established.Basic data such as vertical displacement and horizontal displacement of the points were obtained through the elevation observation and plane observation of the observatory.Periodic survey and measurement of the surface cracks that appear in the zone of the advancing direction of the vertical working face were executed.Using the inflection point theory to assist in verifying the development law of the surface cracks found in the field measurement;combine the drilling geological data of the 11123 working face,and use the FLAC3D software to establish the initial numerical model of 11123 working face,the 11124 working face,the 11125 working face and 11223 working face,studying the evolution characteristics of overlying strata movement such as displacement and stress under repeated mining of different coal seams and repeated mining of the same coal seam when working face 11123 is advanced to 330m,660m,990m,1320m under different mining width and thickness designs.The following results have been achieved by synthesizing the methods of above-mentioned field measurement,theoretical analysis and numerical simulation.(1)Integrating the geological and mining conditions of the 11123 working face under repeated mining and the surface hydrogeological conditions of the working face,a surface movement and deformation observatory for the working face has been established,which provides a reference with the design of the working face observatory in similar mining and surface terrain conditions,simultaneously,provides the basic data for the research of surface deformation laws under repeated mining conditions.(2)The previous method to measure depth of the surface cracks caused by coal mining is improved,using lime powder instead of lime slurry as the tracer,which effectively avoids the measurement error caused by the seepage of the lime slurry poured into the crack.Combining the characteristic point of the inclination deformation curve(the maximum point of inclination deformation)and the characteristic point of curvature deformation(the point where the curvature deformation drops to zero after achieving the first maximum value)of the observation line three of 11123 working face,the position of the inflection point is determined.According to the dynamic movement law of the inflection point,the tensile-compression deformation zone outside the working face is determined,so as to analyze the temporal and spatial evolution law of the dynamic development of surface cracks.According to the six-phase inclination deformation curve and curvature deformation curve drawn from March 21,2019 to December 24,2019,it can be seen that the MS56 point is used as a straight line parallel to the working face,the south area is the extension zone,and the mining boundary area from the north to the mining face downhill is the first extension and then compression zone according to the result that the position of the inflection point has been initially located between MS58 and MS59,then moves to MS57,and finally the inflection point stays at point MS56.Combining the three-stage field investigation and the actual measurement of the crack development near the observation line three,it can be seen that under the geological mining conditions and repeated mining conditions of the mine,the development of the surface cracks in the first extension and then compression interval is a procedure from generating to development and finally to closure.(3)According to the geological data of borehole near the 11123 working face,through rationally integrating and abstracting the primordial formation,a numerical model of totally twenty layers is established based on FLAC3D software.The evolution laws of overlying strata displacement and stress characteristics are studied separately under vertical and horizontal repeated mining conditions where mining width,mining thickness and slicing mining are influencing factors.Mainly through analyzing evolution characteristics of overlying strata displacement and stress under vertical and horizontal repeated mining conditions where the four simulation schemes of 11123 working face advancing three hundred and thirty meters,six hundred and sixty meters,nine hundred and ninety meters and one thousand and three hundred and twenty meters are designed when mining width and thickness is set differentially.It is concluded that mining width has a greater effect on the evolution characteristics of overlying strata displacement and stress under the conditions of vertical and horizontal repeated mining,mining thickness has little influence on the evolution characteristics of overlying displacement and stress under the conditions of vertical and horizontal repeated mining.Figure[52]table[5]reference[72]...