Abstract: The paper has firstly clearly detected and put forward the view of mining-induced failure depth lagging coal wall secondary deepening rule. Moreover, Jincheng, Yulin, Ordos coal mining working faces have been chosen to verify the point of view. By using better field test conditions water injection test and floor rock strain continuity of detection have been implemented to the floor damage rule after the coal wall pushing. The detection results have shown that: 1) Floor rock damage has occurred in the area of stress concentration when the working face is just pushed through the measuring point for the first time. 2) The working face has been 15 m to 20 m pushed away from point. After that point in the first periodic pressure, water-conductive failure depth of measuring point position has appeared secondary lagging deepening, and the degree of damage deepening is 1-2 m. 3) When the working face has been pushed away from point after 2-4 periodic pressure, the deformation state of floor rock in measuring point position tends to be stable. 4) When the working face has been pushed away from measuring point between the 1st periodic pressure and 4th periodic pressure (the working face pushed away from point 15 m to 60 m), the distance is the high-risk areas for backplane lagging water-inrush. 5) Results of bottom water injection test and detection of rock strain detection test are of high consistency.

Key words: floor failure depth, water injection test, secondary deepen, delayed fracture, floor water inrush