(1) Development of deep deposits
Most of the deep deposit development belongs to the deepening work on the basis of the original development project of the production mine, but there are also some of the first development projects belonging to the deep buried ore body. In any case, a pre-design feasibility study is required to reasonably determine the depth of deep deposit development based on the deposit conditions, mining technology and economic conditions. According to the depth of development, the deep deposit construction plan is determined. The original method and method for selecting the development plan and the development task of the deep deposit are basically the same as the shallow deposit development.
In the specific design, it is necessary to determine whether to adopt a single development or joint development according to the characteristics of deep mining; consider the number of sections, positions and numbers of wellbore. The lifting depth of the 25~50t bucket multi-rope hoist can reach 2000m. South Africa's "Brel" multi-rope winding lift has a maximum lifting depth of 2442m. Therefore, for deposits with a depth of less than 2000 m, the mine bed should adopt a single development mode, and the wellbore should be drilled from the surface once or several times to the design depth; or joint development (shaft-shaft; shaft-inclined well).
Under normal conditions, in order to ensure ventilation and transportation materials, the number of auxiliary wellbore in the deep development is more than that in the shallow and medium depth mining.
As the mining depth increases, the original rock stress increases, and the possibility of instability after the roadway is excavated increases. Especially, the mining roadway is more susceptible to instability under the influence of mining. According to the measurement of the original rock stress according to the Jiangxi Dajishan tungsten mine (mining depth 450m), a stress rise zone is distributed in the lower part of the ore body (Fig. 1). The same conclusion was reached when the mining depth in the Crivolog mining area of ​​the Soviet Union was greater than 400 m. Therefore, this must be taken into consideration when considering the development and the layout of the roadway. Especially when the thick ore body is mined by the caving method, the area of ​​the stress increase zone distributed in the lower part of the ore body is large, which causes the stage roadway located in the lower part of the ore body to be damaged by the ground pressure, and the maintenance cost of the roadway increases. In order to ensure the deep mining, the mining roadway is damaged by the mining effect, and the position of the mining roadway should avoid the stress rising zone of the lower plate. Generally located 30 to 60m away from the ore body.
Fig.1 Distribution of stress in the lower plate of Dajishan tungsten mine
(2) Adopting the roadway layout
The layout of the mining roadway shall ensure that the stope has a continuous airflow and the necessary air volume.
In deep mining, it is necessary to understand the characteristics of the original rock stress field during the mining stage, namely the magnitude of the stress and the direction of action. According to the magnitude of the original rock stress, the ratio of the vertical stress to the horizontal stress component, the direction of the maximum principal stress, etc., the shape of the roadway section and its arrangement orientation are reasonably selected. When designing the section of the roadway, try to make the ratio of the horizontal axis dimension to the vertical axis dimension of the roadway section equal to the ratio of the horizontal component and the vertical component of the original rock stress. And the long axis is arranged in the direction of maximum pressure, so that a uniform circumferential compressive stress ring is formed in the rock mass around the roadway, so that the stability of the roadway is guaranteed from the characteristics of the secondary stress field.
For some, in the deep ground pressure, the main roadway should have a curved section (circular, elliptical).
(3) Roadway technology
When the mining depth exceeds 600m, not all mines have geopressure activities with dynamic pressure characteristics. Therefore, depending on the lithology and rock mass structure characteristics, the ground pressure can be selected. At present, the types of support widely used in deep mining mines are: spray anchors for reinforcing rock (self-strength), spray anchor net support; auxiliary strong type of shrinkable steel bracket, rigid mixed soil support. According to the rock damage observation and roadway support experience around the deep mine roadway in South Africa, the technical type can be determined according to the ratio of the vertical stress component (σzz) of the original rock stress to the unidirectional compressive strength (σc) of the rock.
Σzz/σc=0.1 The roadway is stable and does not need support;
Σzz/σc=0.2 A slight piece of help for the roadway gang can be supported by anchor spray;
Σzz/σc=0.3 The roadway has a serious patch, which needs support and can be supported by anchor spray;
σzz / σc = 0.4 reinforced support for an available arch support metal support;
Σzz/σc=0.5 There is a possibility of rockburst, which can be supported by anchor spray net.
Gold mines with deep mining depth in South Africa mostly use concrete support as a permanent support for secondary support. Generally, concrete No. 500 is used, and the wall thickness is 1 m. When using anchor spray or anchor spray net, the length of the bolt is 0.5 times of the width of the roadway, the size of the metal mesh is 6×6～10×10cm, and the diameter of the steel wire is 4.6mm.
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