Study On Rock Movement Caused By Underground Mining In Tectonic Stress-Mines

In tectonic stress-mines, surface deformation and rock movement become complex because of tectonic stresses. During the process of underground mining, the displacement and inbreak angles are often forecasted inaccurately, which leads to unreasonable mine construction planning, a smaller scope of land acquisition and residents relocation, and consequently results in huge economic losses and influences mine production safety. So it is very necessary to study surface deformation and rock movement caused by underground minging in tectonic stress-mines.Taking a typical tectonic stress-mine-Chengchao iron mine as the background engineering, the regulations of rock movement caused by underground mining are studied adopting several means or methods, including engineering geological analysis, comprehensive in-situ cubic observation, as well as theoretical and numerical analysis.The major contents and results are presented as follows:1. Investigates engineering geological and hydrogeological conditions, ore deposit and mining situations in the east and west districts of the mine, and analyze the occurrence and development mechanics of collapse pits basing on geological and mining conditions.2. The main factors of surface subsidence and rock deformation is rock structure character, tectonic stress and self-weight stress, groundwater and underground mining, etc. Underground mining is the efficient amse of rock deformation. The gob's size, shape and location decide the surface's size, shape and location. Only a certain size of gob formed by underground mining, the surface subsidence could occur.3. Lithology of wall rock has an important influence on rock movement and surface subsidence. If the roof rock has a good quality, it will act perfectly as a supporting arch during underground mining, which can effectively slow surface subsidence and reduce the scope of surface subsidence. Besides, special lithology will affect the process and the law of surface subsidence.4. Special geological structures such as faults or rock interfaces have an important impact on the scope of surface collapse. If there is a fault around the pit, it will effectively block collapse to extend across the fault. However joint fissures will speed up surface subsidence and aggrandize the scope of it. Karst in wall rock will form vacuum under the disturbance of the underground mining and groundwater drainage, which will cause surface subsidence.5. Groundwater drainage itself can cause surface subsidence. Groundwater strengthens the deformation of the surface, as a result, surface subsidence maybe occur under special geological conditions such as karst. Groundwater Inrushing can cause sudden deformation and damage of rock.6. Stress field is the driving force of surface subsidence. Larger the stresses and stress differences are, the greater the scope of surface subsidence is. The tectonic stress will increase both the scope and the velocity of the surface deformation.7. Rock movement caused by underground mining in tectonic stress-mines includes four stages, such as gob formation, roof collapse, surrounding rock unloading and deformation and collapse extension weaking.8. In order to analyze the influence of tectonic stress field on the process of rock deformation and damage, the process of rock deformation can be divided into two stages as before and after surface subsidence. For the fomer stage, rock above gob callapses gradually or integral sinking under the action of self-weight stress, and tectonic stress will influence the speed of the subsidence. For the later stage, surface pit will expand under tectonic stress and self-weight stress.