Control of geological structure on coal and gas ou

Control of geological structure on coal and gas outburst in Hebi Mining Area

eight pairs of production mines belonging to Hebi Coal Industry (Group) Company are high gassy mines, of which three pairs in the south are coal and gas outburst mines. Since the first coal production and gas outburst in No. 6 coal mine in 1970. A total of 63 outburst accidents, including outburst, extrusion and dumping, have occurred, posing a serious threat to safety in production and the life safety of workers. In order to explore the law of outburst and the leading factors of outburst. To effectively prevent and control coal and gas outburst accidents, this paper analyzes the control effect of geological structure on coal and gas outburst in Hebi mining area from a geological point of view

1 basic situation of Hebi mining area and gas outburst

coal and gas emptying in Hebi Mining Area occur in Crosscut coal uncovering and coal roadway excavation. The basic situation is shown in Table 1

Table 1 table of outburst in coal roadway excavation of crosscut uncovering

three types of dynamic phenomena of outburst, extrusion and dumping have occurred in Hebi mining area, of which the typical outburst accounts for a large proportion, about 74%; Pressure and tilting force account for 5% and 21% respectively. The outburst inducement is not mainly caused by shooting, and the statistical data are shown in Table 2

Table 2 outburst proportion of different operations

in coal roadway outburst, the proportion of supporting top coal driving coal roadway is large, and the proportion of driving coal roadway along the top is small; The proportion of heading coal roadway up the mountain is large, and the proportion of heading coal roadway down the mountain and near horizontal coal roadway is small

2 highlight the regional tectonic background of the well mining area

Hebi mining area is adjacent to the Neocathaysian uplift belt of Taihang Mountain in the West and the Neocathaysian subsidence belt of North China Plain in the East. It has suffered many tectonic movements such as Yanshan and Xishan during the geological history. The main coal seam in the mining area is 21 coal, with an average coal thickness of 8m. The direct roof of the coal seam is thin-layer sandy mudstone, and the main roof is fine-grained and medium fine-grained sandstone. The whole mining area is a monoclinal structure, and the secondary structure in the area is complex, mainly fault folds. In the mining area, 8 large-scale dip directions and anticlines occur alternately, mostly in the northeast direction. There are also a few secondary short axis folds and asymmetric saddle structures in the mining area, which have lost their complete geometric shape due to the influence of elongated faults. The faults in the mining area are all high angle normal faults, with a drop of more than 100 m. The strike is mainly NE or NNE. Many stepped small faults are often developed in the two walls of large faults, forming a wide fault fracture zone. In addition to faults, x-conjugate shear joints and fissures are also very developed in coal seams and coal seam roof and floor, resulting in coal rock fragmentation

the controlling geological formation of the mining area is qingyangkou fault, which is an associated fault of Jingguang fault. The strike of the fault is more than 100 km long, with a maximum drop of 1000m, and extends from north to East. The fault is closest to the southernmost Shikuang mine in the mining area, passes through the deep part of Shikuang mine and gradually deviates from the mining area to the north. The primary faults in the mining area are the Jiajia graben and the F40 fault group, with a cumulative drop of more than 200m. The mining area is divided into three relatively independent parts: three pairs of Mines of No. 6 mine, No. 8 mine and No. 10 mine in the south, two pairs of Mines of No. 3 mine and No. 2 mine in the middle, and three pairs of Mines of No. 2 mine, No. 4 mine and No. 9 mine in the north. Liu Dongsheng's research team took the lead in preparing a new type of DNA hydrogel material mine in the world. Under the action of two-level fault structure, the gas geological conditions of the three pairs of mines in the south are quite different from those in the middle and North:

(1) the complexity of geological structure in the mine field is obviously different. There are more faults cutting and inserting each other in the 3 pairs of mines in the south, while there are less faults in the 5 pairs of mines in the north; In the three pairs of mine fields in the south, especially in the sixth mine field, there are more folds in different directions intersecting each other to form domes or tectonic basins, while there are fewer in the five pairs of mines in the north

(2) the occurrence of coal seams in 3 pairs of mines in the South changes greatly, and the dip angle is significantly larger, generally up to 30 ° in the deep and 50 ° in some parts. The dip angle of coal seams in 5 pairs of mines in the north is generally below 20 °. The increase of coal seam inclination makes the self weight stress become the inducing factor of coal and gas outburst, which is obvious when supporting the top coal to drive up the mountain. The three outburst accidents of "9.25", "3.19" and "4.10" in No. 10 coal mine were all caused by the top coal caving

(3) the thickness of coal in the three pairs of mining areas in the South varies greatly, with relatively more thin and thick coal zones, and the thickness of local coal seams varies between 0~12m, which is far from the average coal thickness of 8m. Coal thickness change zone is often a serious outburst danger zone

3 control effect of geological structure on outburst

comprehensive analysis of the characteristics of coal and gas outburst accidents in Hebi mining area is basically controlled by geological structure. Geological structure controls coal and gas outburst by controlling the development degree and range of structural coal, the distribution of in-situ stress, and the occurrence and migration of gas

3.1 geological structure has a very serious impact on the physical and mechanical properties of coal, which is mainly shown by the development degree and distribution range of structural coal. Compared with the five pairs of mines in the north, the development of structural coal in the three pairs of mines in the south is very obvious and common. The observation shows that structural coal is widely developed in the three pairs of mines in the south near the fault and the axis of the syncline and anticline; In the non structural zone, because the thickness of the gangue at the distance of 1.5m~2.0m from the coal seam floor of the three pairs of mines in the south is only 0.3~0.5 times that of the five pairs of mines in the north, the rock mechanical strength is seriously reduced. Under the influence of strong geological structure, a large area of layer slip structure occurs in the coal seam. This is a kind of interlayer sliding structure in which the coal seam does not stagger, but the roof and floor of the coal seam are relatively displaced. The gangue with small thickness often plays the role of sliding surface due to its weak adhesion with the upper and lower coal seams. Generally developed structural coal is formed at the bottom of the coal seam by the layer slip structure. Using the classification method of four types of structural coal, the whole coal seam near the fault and the axis of the syncline and anticline is class III and IV structural coal, and the development is basically class III and IV structural coal. The actual measurement shows that the coal strength of class I coal (non structural coal) in each mine is basically the same, and the firmness coefficient is 0.41~ 0.55。

the actual measurement shows that the coal strength (? Value) of class I coal to class IV Coal in the three pairs of mines in the south is significantly different, as shown in Table 3

Table 3 what are the three pairs of mines in the south? Value

the existence of structural coal reduces the coal strength, that is, reduces the resistance to prevent outburst. Structural coal, which is very obvious and common in three pairs of mines in the south, has become one of the factors of coal and gas outburst

3.2 control effect of geological structure on in-situ stress

two major tectonic movements in Yanshan and Xishan in Xuezhong during the geological history, the superposition of six mine fields, caused the in-situ stress of three pairs of mines in the south to be significantly larger. The measured value of in-situ stress in liukuang mine shows that the heavy direct stress is 1.05~1.78 times of jinnick's theoretical value, while the horizontal stress is 2.69~4.76 times of metal Nick's theoretical value, and the distribution is very uneven. The measured value of stress also shows that there is a large shear stress in the coal measure strata of No. 6 coal mine. The existence of residual tectonic stress plays a role in stimulating outburst, which greatly increases the risk of coal and gas outburst. The calculation results show that the elastic potential of the coal body in the brick and tile compression state in the No. 6 mine is about 4 times that of the gas internal energy, which is the main driving force for breaking the coal body and stimulating outburst, and the main excitation factor for coal and gas outburst

tectonic stress also causes further superposition of stress through the supporting stress formed by mining activities, which is prominent in Japan as one of the most developed countries in carbon material industry. The "9 · 12" and "12 · 5" outburst accidents in No. 6 mine are the result of support stress. The "9 · 12" accident was: 20m was left due to the treatment of the fault during the mining of the top layer of a working face × 30m, 15m after the lower layered Island excavation, it was in the middle of the island, and a outburst accident occurred, with the amount of coal outburst of 85t and the amount of gas of 1800m3; " 12.5 "the accident is: in order to transform the upper chute of a working face, an additional one was excavated in parallel at the place 2.5m away from the upper chute of the original coal seam floor, 2m from the bottom. After the blast, an outburst accident occurred, with the outburst coal volume of 140t and the gas volume of 2600m3. The outburst gas volume of ton coal in both accidents is only slightly higher than the ton coal gas content, which is similar to the typical outburst ton coal gas output (5~9 times the ton coal gas content) There is a large difference compared with that, so the prominent force is mainly the support stress

3.3 control effect of geological structure on gas

the control effect of geological structure on gas is mainly manifested in gas content, gas pressure, gas emission speed, etc. See Table 4 for the measured gas pressure and adsorbed gas content of each mine

Table 4 measurement of gas pressure and adsorbed gas amount of each mine

the measured results show that gas pressure is closely related to geological structure and coal seam buried depth. With the increase of buried depth, the gas pressure increases; The structure of the three coal mines in the south is complex, the permeability of the coal seam is poor, and the gas content is closely related to the buried depth and coal quality. With the increase of buried depth, the gas content increases; The coal seam water content of No. 10 coal mine is high. Generally speaking, the gas pressure and gas content of the current mining level in Hebi mining area are generally higher than the critical value of outburst. Therefore, what controls the occurrence of gas outburst is the gas emission speed in mining activities

the development degree of structural coal determines the initial velocity of gas emission in the mining process. Measured initial velocity of gas dispersion（ Δ P) See Table 5

Table 5 Relationship between initial gas velocity and coal type

the measured data show that the initial emission velocity of class IV structural coal is 2~3 times that of class I coal. Structural coal is destroyed, deformed and depressurized after being subjected to mining concentrated stress, and adsorbed gas is rapidly desorbed, forming a large number of free gas with strong expansion energy. Under the excitation of concentrated stress, the coal body is transported and broken, so as to promote the occurrence and development of coal and gas outburst

4 conclusion

(1) coal and gas outbursts occurred in 3 pairs of mines in the South and 5 pairs of mines in the north of Hebi mining area, which is the result of regional geological structure control. Geological structure is the result of controlling structural coal, in-situ stress and gas. Geological structure controls coal and gas outburst by controlling structural coal, in-situ stress and gas. At the present mining level, the development degree and scale of structural coal are the key factors of coal and gas outburst

(2) the development part of structural coal is the key point of outburst prevention in Hebi mining area, and the outburst prevention work of structural belt and bottom layered coal roadway excavation needs to be strengthened. At the same time, the prediction and detection technology of geological structure should be actively studied to provide geological data for the prediction and prediction of coal and gas outburst

(3) to prevent and control coal and gas outburst, pressure relief and enhanced comprehensive outburst prevention technology should be adopted, that is, through the drainage of boreholes and gas drainage, the in-situ stress, gas pressure and gas content should be reduced, and the strength of structural coal should be increased accordingly. At the same time, improve the roadway support strength, ensure that the resistance of outburst is greater than the power, prevent coal and gas outburst accidents, and realize safe production