Overlying strata movement law and spatial structure analysis of fully mechanized mixed mining of backfilling and caving

The deep mining faces in No. 12 coal mine in Pingdingshan have an engineering background of a large a- mount of waste,transportation difficulties,mine environmental pollution and conventional filling surface production ca- pacity. An innovation of fully mechanized mixed mining of backfilling and caving (MMBC) is developed and the char- acteristics of technology are introduced. By means of theoretical analysis,physical similarity simulation and field meas- urement,the spatial structure characteristics of the fully mechanized mixed mining coal face are studied systematically. The influence of backfill ratio on the strata spatial structure was theoretically analyzed. The physical simulation results show that in the backfilling section of the mixed mining face,the basic roof only bends and sinks,immediate roof ca- ves,and some basic roof fractures occur in the caving section. The basic roof subsidence in the caving section is 4. 2 times the average of that in the backfilling section which shows the obvious characteristics of asymmetry. In-situ meas- urements show that the stope pressure in backfilling section is not obvious,while it is significant in the caving section. The first weighting step is about 30 m,and the periodic weighting step distance is about 22 m,also the dynamic load coefficient is about 1. 7. The rock borehole results show that roof is intact and strata spatial structure shows “two belts” development characteristics in backfilling section;the immediate roof caves,and basic roof breaks in the caving sec- tion,overlying structure has the “three zone” development characteristics,which shows the obvious characteristics of a- symmetry.