The mechanical model of the overburden rock under mining and the broken condition analysis

According to the broken mechanism of the overburden rock under mining, the mechanical model in before and after initial caving is established. Based on the model, the broken condition of the overburden rock is analyzed by using the beam bend theory. By considered the factors of strata character and its thickness and depth, a calculating model of the critical extraction length when the overburden strata break down is established. Then a calculation example is given to analyze the condition.