Origin of ground collapse at the Sujiazhuang iron mine in Jinan City

Based on the survey to geologic conditions and exploitation situations at the Sujiazhuang iron mine，the features and origin of ground collapse is expounded by means of the analysis on geophysical features, sinking and driving engineering, groundwater table and engineering geologic features of the ore body an d surrounding rocks. The results show that the horizontal change of apparent resistivity isoline is relatively gentle within the 200 m probe scope with transient electromagnetic method and that there is no obviously abnormal distribution of goaf; the total volume of goaf is only about 9 218 m3 that is much smaller than the total volume, 58 665.8m3, of the collapse pit; the water head between the shaft and collapse pit and that between the collapse pit and goaf are very high and stable, up to 58.93～64.11 m; the integrity and intensity of the surrounding diorite and limestone as well as marble are quite well, so the probability of ground collapse led by goaf collapse is very small. According to the above situation and the comprehensive analysis on the landform, stratum structure, overlying cap, dynamic conditions and mine drainage as well as other factors, it is believed that the ground collapse is caused by long term pumping during exploitation.