Analysis of the surface deformation characteristics and strata movement mechanism in the main shaft area of Chengchao Iron Mine

The surface deformation and strata movement caused by underground mining in a metal mine often exceeds the designed range, which can destroy main shafts and other key structures, causing huge economic losses and affecting production safety. Here, the main shaft area of Chengchao Iron Mine affected by tectonic stress is analyzed. Detailed monitoring data from the past 11 years were used to analyze the surface deformation characteristics and the strata movement mechanism. The results show that the surface deformation in the main shaft area shows S-shaped curve characteristics comprising a stable deformation stage, a rapid deformation stage and a stable deformation stage. The surface horizontal displacement vector in the main shaft area points to the western mining area, indicating that the surface deformation in the main shaft area is mainly affected by underground mining in the western area. From December 2007 to December 2009, the expansion of the movement line ($\epsilon$ = 2 mm/m) was small; in December 2009, the expansion of the movement line increased significantly. The expansion law of the break line ($\epsilon$ = 6 mm/m) was similar to that of the movement line. Furthermore, the movement angle decreased significantly from December 2009 to December 2011, and the break angle sharply decreased from December 2010 to December 2012. The cantilever beam mechanics model revealed that the fractured width of footwall in the direction of the main shaft area was 266 m. When exploitation reaches a horizontal depth of − 600 m, the fracture width is predicted to reach 402 m.