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Main factors affecting the stability of surrounding rock in empty area
The formation of goafs redistributes the stresses of a certain range of rock masses around them, resulting in rock deformation, damage and movement. If the amount of fallen rock does not eliminate the empty area, another cycle of deformation, displacement and damage will occur at the boundary of the new empty area. The form, extent and time of rock mass movement and damage caused by empty areas are restricted by a series of factors, some affect only underground production, and some affect the surface, surface cracking, subsidence and collapse, in certain terrain. Under conditions, landslides, landslides, rolling stones, mudslides, etc. may occur.
Rock mass instability and movement mainly depend on rock properties, rock stratum structure, geological structure, mining depth, ore body dip angle, mining method, pillar and its recovery status, empty area shape, scale, empty area existence time and treatment method, Hydrogeological conditions, surface topography and other factors. Under the influence of different factors, the rock mass movement shows different characteristics, and the degree of influence is also different.
Rock properties, especially physical and mechanical properties, are one of the main factors affecting the stability of the empty zone and the process of rock movement. The particularity and complexity of rock properties are the main reason for the complexity of rock mass movement problems.
The weak surface formed by various structures (faults, joints, fissures, layers, fracture zones, etc.) in the rock mass reduces the strength of the rock mass. The majority of our metal and nonmetal mines large-scale rock movement examples show: rock often start moving along the large surface structure is weak, mostly cracks when moving the development and expansion of the existing weak side. It can be said that the weak surface of the geological structure affects the development of rock mass movement caused by mining to a considerable extent, and controls its expansion range.
Rock inclination determines the occurrence region of feature space, thus affecting the stress state and the failure process of top and bottom slate stone. The roof rock stratum in the central part of the gently inclined ore body is generally subjected to compression and sinking. Then the crack is broken; the ore or surrounding rock adjacent to the unextracted section is mostly shear damaged. The sloping prism on the upper plate of the steeply inclined ore body is mostly shearing. The dip angle of the ore body increases, the horizontal movement of the ore body increases horizontally, and the range of movement of the rock mass increases; while the normal component of the gravity of the cover rock subjected to the upper plate decreases. Therefore, the empty area formed by the steeply inclined ore body mining has better stability at a certain depth, but the mining depth is increased and a large-scale empty area is formed, and there is a possibility of sudden large-scale collapse.
The empty areas of different dip ore bodies have different effects on the ground surface. Under the same conditions of the goaf area, in the unit area, the steeply inclined empty area has a more concentrated damage effect on the surface affected area than the gently inclined empty area, and it is easy to be broken by the plunger type vertical shear. In the treatment of empty space effect, there is also a difference between the two, regardless of the filling method or caving method to deal with the empty area, when the loose body compression rate is the same, the larger steep inclined ore body goaf is not easy to maintain stability, the loose body is easy to follow the mining Falling and moving down or falling down is one of the reasons for the constant settlement of the earth's surface.
The depth of mining, the size of the empty area and the time of existence have a great impact on the movement of the rock mass.
Most of the steeply inclined thin veins are in mountainous terrain and exposed to the surface. The surface rock movement caused by the mining empty area has different characteristics depending on the mining depth and the intensity of the vein group. When the pulse group is sparse and the pulse distance is more than 20~30m. When the mining depth is shallow and there are a certain number of pillars supporting the empty area, the rock mass movement and surface collapse caused by mining are less; the vein group is dense, the mining depth is increased, and Causes large-scale rock mass movement and destruction of the surface. The rock mass movement in the goaf of the steeply inclined tungsten vein group in the central and southern regions is mostly in the above-mentioned law.
Under normal circumstances, the empty areas of shallow thick ore bodies are easy to develop to the surface, leading to surface subsidence and destruction; the deepening of the mining depth increases, the time required for the movement of the two gangs in the empty area to the surface is increased, and the area affected by the surface is also It will increase accordingly; if the depth of mining exceeds a certain value, the rock movement may not affect the surface or influence.
When the goaf is not filled, the thickness of the ore body is an important factor in determining the height of the caving. The larger the thickness, the more intense the rock migration process, the more the rock sinking and other deformations increase, and the ore body is particularly flat.
When the rock mass moves to the surface, the depth and thickness of the mining affect the size of the moving angle. The maximum sinking value of the surface is related to the degree of mining. When fully plucked, the surface sinks to a maximum and no longer increases with the increase of the empty area. In metal mines, due to large changes in ore body shape, some continuous empty areas are small in scale, and most of them are not fully exploited, and the maximum sinking value of the surface increases with the increase of goaf.
The size of the empty area directly affects its stability and the range of rock movement activities. Large-area continuous empty areas are more likely to fall, and the range of rock movement is large. When adjacent airspaces are close together, their effects can contribute to each other and the damage is exacerbated. When the total amount of underground space is the same, if it is divided or isolated by a pillar or a non-mineral belt with sufficient strength, its stability is improved and the rock movement amplitude is reduced. At the same horizontal area, the length and width values ​​are close. A large span has a larger difference than the length and width values, and a smaller span is more likely to collapse.
The mining method and the empty area treatment method are different, and the rock mass movement characteristics are different. The empty area is treated by the caving method or the post-harvest collapse rock method. The rock mass movement can be fully developed and is easy to develop to the surface. When the overburden is stable, its caving may lag behind the recovery and form an empty area. To ensure the safety of the mining, a rock cavern of sufficient thickness should be maintained under it. The use of filling method or post-harvest filling treatment of empty areas can better control or reduce the amplitude and intensity of rock movement. The movement process has a gentle feature. Even if the rock movement develops to the surface, its impact range and damage to the surface. The degree is also small. When the empty section is supported by the permanent pillar, as long as the stability of the surrounding rock and the strength of the pillar are sufficient, the empty zone can be stabilized for a long time. However, when the area of ​​the empty area is enlarged, the time is too long, and the pillars are overloaded and destroyed, which will cause large-scale collapse of the rock formation and may affect the surface. The impact and vibration of large blasting affect the stability of the empty area; the practice of some mines proves that the destruction of the pillar and the collapse of the empty area are often related to the large-scale blasting of adjacent sections.
When the terrain is gentle, the movement of the surface rock mass generally takes the form of a submerged basin or a collapsed funnel, and the scope of influence is limited to the moving belt formed by the empty area. When the terrain is steep, the development of the rock in the empty area to the surface may cause landslides, landslides, rolling stones and mudslides. Its intensity and reach often exceed the range of the entire rock movement.