Study On Geology Stability Of Old Mined-out Area In The Condition Of Repeated Coal-mining

In recent years, detection and research of coal mined-out area is not only a hotspot of geophysical prospecting, but also the guarantee of coal mine safety production and mining area environment protection. In the view of the lack of geological data, repeated mining, the characteristics of old mined-out area is both complex and irregular. There is no mature theoretical system in response to this phenomenon, so, the studies on detecting old mined-out area by using the integrated geophysical exploration technique will be of great significance. This article based on the research status at home and abroad. For the purpose of geological stability evaluation of old coal mined-out area, researchers analyzed and discussed the formation and characteristics of old mined-out area by collecting a large number of basic data and theoretical methods, outdoor survey and comprehensive geophysical prospecting, shallow drilling, surface soil fertility evaluation and indoor experimental analysis, which got the following points:(1)Steady old mined-out area is easily to be activated under the condition of repeated mining by small mines, causing the rock collapse and deformation of surface residue. And changes about geophysical characteristics which is caused by the destruction of the integrity and continuity of original rock is the theory premise of comprehensive geophysical prospecting.(2)By the way of engineering cases, the effectiveness of detecting old mined-out area by using the comprehensive geophysical prospecting of parallel network, Transient electromagnetic and 2-dimensional seismic method are explained.(3)Integrated geophysical detection results show that the apparent resistivity has significant difference in both vertical and horizontal.Parallel network electricity method has relatively high resolution for anomaly inversion, which can remedy the shallow survey blind area of the transient electromagnetic method, whereas the transient electromagnetic method has the advantage of detecting greater depth and high resolution for low resistivity anomalies. Two-dimensional seismic method also shows the location of mined-out area, which is consist with the result of electrical prospecting. The combination pattern of integrated geophysical methods improve the reliability of exploration results and provide a meaningful reference for detecting other old mined-out areas with similar conditions.(4) Researches about the quaternary clay layer shows that the thickness of clay layer soil is stable, which effectively cut off the surface water by infiltration recharge of groundwater, provides favorable conditions for wetland ecosystem reconstruction. Degree of surface soil fertility in the study area is low, fertility increased from west to east, which has certain spatial correlation with the surface subsidence. Aggravated soil erosion is the main cause of soil fertility spatial differences in the study area.(5) Comprehensive evaluation about geological stability shows, due to the repeated mining of small coal mines, central and east of the study area is non-stable region. After decades of residual subsidence and overburden pressure process, other area which is not affected by small coal mines, is basically stable.