Classification of mining site pressure activities and influencing factors

    I. Classification of mining site pressure activities

According to the ground pressure, the characteristics, the scale of the activity and the degree of damage can be divided into two types: localized ground pressure and large area ground pressure. The former has a small spread (1 to several stopes), which has little impact on production and safety, and is slow to develop (months to decades); while the latter has a wide range (several stages), which is destructive and develops rapidly ( Hours to several days), which seriously affects production and threats to safety, and even the whole mine is shut down, causing significant resource losses. Taking Jiangxi tungsten mine as an example, the ground pressure is classified in Table 1.

Table 1 Classification of pressure activity in tungsten mining

Due to the small scale and slow development of localized ground pressure, if effective control measures are taken in time, large-scale ground pressure can be avoided. Conversely, when the local pressure is out of control, the ground pressure increases rapidly, and as a result, a large area of ​​ground pressure may be caused.

    Second, factors affecting the pressure of mining sites

(1) Gob area

The volume of the goaf is a factor that is unfavorable to the stability of the rock mass with the size of the mining and the recovery time. It is related to the geometry and spatial distribution of the ore body. Generally speaking, the larger the volume of the goaf, the worse the stability of the rock mass, especially the larger the volume of the continuous empty space, the more sufficient the conditions for inducing the ground pressure activity. . Former tin ore mine south ground pressure occurs, there is 815,000 meters underground mined-out area ^3, Pangushan tungsten ore is 1.789 million m ^3, Gongchangling iron ore is 92 million ^m3. Judging from the reasons for the occurrence of ground pressure activities in some old mines in China, the goaf is the root cause of ground pressure activities.

(2) Time effect

The large amount of observations obtained in mines with ground pressure indicate that time is an important variable under other conditions. Because of the large-scale activities of the rock mass, there must be a development process. From the relationship between rock movement and time measured by tungsten deposits such as Tieshan Ridge, Xiaolong, Dajishan and Tumei, Jiangxi Province (Fig. 1, Fig. 2), it is seen that the ground pressure activity has a slow movement, accelerating the movement and collapse. process. Local ground pressure activities, some local collapse, and some no collapse, which is determined by other conditions (such as lithology, rock mass structure, etc.).

Fig.1 Relationship between displacement of rock mass and time in 518 stage 110 Dongda alley of Jiangiayu mining area

(Local type of ground pressure type, 30m roadway collapse around 6141 measuring point)

1-6141 measuring point; 2-6145 measurement; 3-6146 measuring point; 4-6153 determination

Fig. 2 Relationship between displacement and time of unstable rock mass in Xiaolong Mine (type of large-scale ground pressure activity)

1-14 ^#测点;2-15 ^#测点;3-16 ^#测点;4-K ₅点点

(3) Structure weak side

Observations have shown that for large-scale ground pressure activities, large continuous structural weak surfaces (such as faults, fracture zones, etc.), on the one hand, control the occurrence of large-scale damage, that is, the cutting surface or sliding surface that becomes the moving boundary of the rock mass; Aspects promote the acceleration of its occurrence and development. It is observed from the surface of the Gongchangling iron ore mine that the surface crack caused by the underground ground pressure activity generally occurs along the fault and thus forms a sinking step. Antimony tin ore mine, Pangushan tungsten ore, phosphorus ore Jingxiang larger rock moves, geologic formations subject to the control plane of weakness.

(4) Mining depth

The gravity of the overburden is directly proportional to the ground pressure. Generally, the greater the depth of mining, the greater the ground pressure. If there is a structural influence, the horizontal stress is often greater than the vertical stress.

(5) Groundwater

On the one hand, groundwater acts as a melting, softening and muddy on the rock mass structure surface, which reduces the strength of the weak surface; on the other hand, under the action of the fissure water pressure, the frictional resistance acting on the crack surface is reduced, thereby reducing the rock mass. Shear strength. The large-scale ground pressure activities of Jiangxi Tungsten Mine and Gongchangling Iron Mine generally occur during the Spring Festival thawing or rainy season.

(6) Mining technology

When the geological conditions of the deposit are certain, the mining sequence of the ore block, the structural parameters of the ore block, and the mining process have an important impact on the pressure of the mining site.