Fine detection for the deformation failure of overburden strata caused by underground mining may provide reliable guidance for safety,high efficient and green coal mining.Firstly,the principle of overburden detection based on time lapse high density resistivity method was investigated.Then 3D geologic-geophysical models of overburden strata before and after mining were constructed,and the corresponding numerical simulation was carried out by using these models.It is demonstrated that deformation failure of overburden strata is hourglass-like in the resistivity change rate profile and orifice is the separatrix between the fractured zone and the bending zone.Furthermore,field tests were carried out,results show that the surface subsidence caused positive anomaly and precipitation caused negative anomaly in the resistivity change rate profile.Based on the hourglass-like anomaly morphology and key stratum layer,the height of fractured zone was determined to be 98 m.Finally,the results from time lapse detection were verified by drilling results.
