At present, many mines in the United States adopt the stage natural caving method, and this method is rarely applied in China, but the history of this method is still relatively long (about 50 to 60 years). This method is strictly used, so it is not widely used in China (nearly). Â
(1) The essence of the natural caving method at the stage.
This method is essentially: at the bottom of the nugget, a certain area of ​​the bottom is pulled, in the side of the state, after appropriate cutting, by the ore weight and the pressure of the upper complex rock, the ore of the height of the natural collapse process, The stage natural caving method is the result of further development of the sublevel caving method.
In ores with natural caving properties, after a sufficient area of ​​bottoming, the ore will gradually collapse due to its own weight and upper rock pressure, but this process is limited to the range of natural balance arches. Here, the ore above the balance arch is in a state of stress equilibrium, thus stopping the natural collapse. In order for the ore to continue to develop upwards and naturally collapse the ore, it must be continuously destroyed, and the natural arch stress balance state.
There are two methods for stress-balancing the natural arch: 1 Enlarge the area of ​​the bottom, so that the arch base moves horizontally and outside the block. For various reasons (more difficulties), it cannot be used in actual production. 2 In the vertical direction, the arch base support point is continuously moved upwards, and the ore is collapsed within the scope of the nugget. To this end, the bonding force between the ore and the surrounding must be weakened locally or wholly in the side of the ore block. This method is commonly used in production.
With the development of the ore caving process, about 1/3 or so of ore is released. At the same time, the rate of ore discharge and the amount of ore released should be compatible with the development of natural caving. The mining speed is fast and may cause a large phenomenon. On the contrary, it will affect the normal development of the natural caving process. Therefore, the ore-mining work of the method in the process of caving is an important means to control natural collapse.
(2) Main advantages and disadvantages
Advantages: 1 High mining intensity and high labor productivity; 2 Low recovery cost and low material consumption.
Disadvantages: 1 Strict requirements for use conditions, small application range; 2 complex mining work (natural collapse is difficult to control, mining is complicated)
(3) Appropriate conditions: 1 Under certain conditions of the bottoming area, the ore has natural cavitation, but no oxidizing, agglomerating and natural. 2 The thickness of the ore body is generally not less than 25 to 30 meters (suddenly inclined ore body); 3 the ore body does not contain a large amount of rock interlayer; 4 the surrounding rock preferably contains beneficial minerals.
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