Study On Evolution Characteristics Of Overlying Strata Movement Of Goaf In Strip Mining

In order to meet the needs of economic and social development,coal mining cities in the central and eastern part of china have carried out large-scale and super-intensive mining of coal resources in areas with relatively dense population and buildings,leaving behind a large number of strip mining goafs.With the development of urban expansion and transformation,coal mining cities are in urgent need of a large number of construction land,while the inventory of them are seriously inadequate.In order to alleviate the situation of urban construction land tightening,scientific management of strip mining goaf makes it an effective way to restore the function of construction land above the goaf.The study on the evolution of overburden movement characteristics in strip goaf is the basis of ensuring the safety of new buildings on the surface above.Compared with longwall mining goaf,the residual pillars of strip mining goaf support the overlying strata and control the surface movement and deformation.While the overlying strata of strip mining goaf remain relatively stable,their movement state may change under the influence of various factors,among which the evolution of pillar support characteristics is particularly important to the movement characteristics of overlying strata.In addition,the response mechanism of goaf overlying strata movement is not clear in the process of strip pillar bearing evolution.Therefore,the study on the evolution characteristics of overlying strata movement in strip goaf has important theoretical value for the further study of disaster prevention and control in goaf,and can provide scientific theoretical guidance for the construction of new buildings above goaf.In this paper,the evolution characteristics of overlying strata movement in strip goaf are studied.Based on the evolution characteristics of strip pillar bearing capacity,theoretical analysis,mechanical test,simulation of similar materials,numerical simulation and other technical means are used synthetically.The structural failure characteristics,stress response mechanism and movement and deformation law of overlying strata in strip goaf are analyzed.(1)Aiming at the failure characteristics and deformation mechanism of strip coal pillars during load-bearing process,the compression test of large-scale cuboid coal samples was carried out by using the long-term load-bearing test monitoring device independently developed by the research group,The progressive failure process of strip coal pillar is simulated and studied,and the progressive failure mechanism of strip coal pillar is analyzed,and the progressive failure law and deformation evolution characteristics of strip coal pillar are obtained..The failure of strip coal pillars occurs gradually from the edge to the interior.The failure process can be divided into fracture compaction stage,stable growth stage,step deformation stage and failure stage(2)A new type of temperature-controlled analogue material was used to replace the conventional analogue material.The temperature-controlled condition simulation and the indoor mechanical pre-test were carried out The main control parameters and the deformation law of the simulated specimen were obtained.Through the similar material simulation test,the movement evolution characteristics of overlying strata in strip goaf during coal pillar bearing process are preliminarily explored.The overlying strata near the boeder of strip coal pillars undergo secondary migration due to the decrease of support capacity at the edge of coal pillars.The increase of the height of overlying strata caving zone in goaf restores the stress of floor after compression,but it still does not reach the initial stress state.Strip coal pillars show higher stress concentration near the core area,and the stable stress area in the core area shows a decreasing trend(3)Based on the simulation test results of similar materials,the numerical simulation model of strip mining engineering is established,and the numerical simulation of the evolution characteristics of goaf overlying strata movement based on the evolution characteristics of strip pillar behavior is carried out.At the same time,the stress response mechanism and the law of movement and deformation in the evolution process of goaf overlying strata movement are further discussed.The stress of overlying strata roof in goaf decreases gradually with the decline of bearing capacity at the edge of coal pillar.As the effective support area of coal pillar decreases,high stress concentration occurs at the boundary of elastic zone and yield zone.During the progressive process of pillar failure,the overlying strata on both sides of the pillar appear larger subsidence movement,the caving height of the goaf increases,and the overlying strata in the goaf will continue to change with the expansion of the yield zone of the strip pillar.