Dynamic evolution law analysis of overburden separation and water flowing fracture under mining based on distributed optical fiber and information entropy theory

The water inrush from overburden separation is large and destructive, which is very easy to cause serious casualties and property losses. Therefore, a three-dimensional model of 150 cm x 150 cm x 60 cm (length x height x width) is established in the laboratory. And the dynamic development process of overburden separations and water flowing fractures in the process of coal mining in real time are analyzed based on distributed optical fiber and information entropy theory. The distributed optical fiber strain curve can well reflect the process and characteristics of overburden deformation and collapse. The strain curve of optical fiber shows a single peak or step shape at different mining stages. The separation position corresponds to the peak of the optical fiber strain curve or above the step. The change of strain value of optical fiber reflects the development, expansion and closure process of separation. The development height of the water flowing fractured zone corresponds to the lower part of the step of the strain curve. Strain information entropy realizes quantitative analysis of overburden system state. Strain information entropy can be divided into small amplitude rapid fluctuation period, sharp rapid adjustment period and stable slow fluctuation period. Water flowing fractures and separations are mainly produced during the period of the sharp rapid adjustment period. The height of the water flowing fractured zone and the height of the new separation increase step by step with the advance of the working face. The water flowing fractured zone finally develops to 86 cm of the model height. The highest position of the separation appears at the 112 cm height of the model. A new variable named growth rate of strain information entropy is defined, which can reflect the severity of the change of the overburden system state. When the key stratum breaks, the growth rate of strain information entropy increases significantly, which show that the key stratum plays a key role in controlling the overburden deformation process. In addition, the optical fiber strain curve can also reflect important information such as the change of advance support pressure, the distribution state of gangue in goaf and the breaking characteristics of key strata.