Structural evolution of overburden and surface damage caused by high-intensity mining with shallow depth

In order to understand the evolution law of overburden structure,and the law and mechanism of surface damage under different mining conditions in shallow high-intensity mining,the numerical simulation,field measurement,theoretical analysis and other means were used to study the typical working face in Shendong mining area. Firstly,the evolution law of overburden structure was analyzed with the peak stress value of goaf as the index. Secondly,the relationship between the surface subsidence coefficient and the ratio of width to depth was explored. Finally,based on the measured characteristics of surface crack development,the mechanism of surface crack development in the middle of working face was studied. The results show that ① the overburden undergone three stages,the first stage was no pressure arch stage. The second stage was single pressure arch stage. The third stage was double pressure arch stage,which was also divided into two stages,i. e. Ⅲ1 ( single arch foot stage in goaf) and Ⅲ2 ( double arch feet stage in goaf). ② The surface subsidence coefficient and the ratio of width to depth obtained from 14 schemes were approximately parabola with the ratio of width to depth between 0. 4 and 2. 0. The measured and predicted subsidence coefficients of seven working faces in Shendong mining area were selected for comparison and verification,with errors of 7.6% ,14. 5% ,4. 4% ,7. 5% ,9. 7% ,9. 7% and 15. 3% respectively,among which the errors of five working faces were within 10% ,and the overall error was small. ③ The development of surface dynamic cracks in the middle of working face have the characteristics of “ double period+stable period”,including five development stages,namely,crack width increasing stage,crack width decreasing stage,crack width stabilizing stage,crack width reincreasing stage and crack width reducing stage. The dynamic development mechanism of crack in the middle of working face was explained through evolution model,and the relationship model between crack dynamic development and geological mining conditions was established.