High-voltage transit lines

gas and petroleum pipelines

riverbeds and other facilities located in mining disturbed zones are extremely sensitive to surface dynamic movement. Based on the case of coal mining under Jinsha river in Gansu province

in-site surface movement monitoring is carried out; and the dynamic law of surface subsidence of fully mechanized top coal caving mining under the thin alluvium is obtained. The study shows that the surface subsidence experiences a very short initial period and a longer active period of movement. The active period of surface movement appears in the range from 110 m in front of the working face to 400 m back of working face

which lasts 185 days and results in 90.7% of the total surface subsidence. The severe period of surface subsidence occurs at 50 m to 150 m in the rear of working face; but the severer movement time is relatively short about 60 days. Based on the sinking curves of the measuring point displaying S-shaped distribution

and the sinking rate curves that are similar to normal distribution

the dynamic model of surface subsidence and sinking rate are established with respect to the mining time and advancing rate. The trajectories of ground measuring points are captured showing the back and forth moving characteristics. The fractures on the surface induced by mining under thin alluvium intend to develop parallel to the mining direction. With the working face advancing

the time and space features demonstrate that the surface fractures move forward and the concentration areas expand to the outside of the mining area.