Ground pressure mining method

    I. Characteristics of ground pressure in the mining method of room and pillar

When the level of the mining rock is stabilized and the ore body is gently inclined, the comprehensive method and the room and column method are generally used.

The Hunan tin mine antimony ore with nearly a hundred years of mining history is a typical example of large-scale ground pressure activities after mining of this type of ore body.

The deposit is mainly hydrothermal filling after the magma period, and the single sulfide sulphide deposit accompanying the replacement has a layered output with a length of about 1500 m, a thickness from thin to medium thickness, a gentle slope, and a dip angle of 10 to 35 °. 250m. The roof of the ore body is shale , ƒ=3~5, unstable, and the bottom plate is stable silicified limestone, ƒ=10～18. Faults and joints in the mining area are relatively developed.

Mining by room and pillar method, the mine is 8~10m wide (bolt top), or 10~15m (0.8~1.0m for retaining top mine), 3×4m (bolt top) for intermittent pillar, or 4 ×5m (retaining mine protection roof), the inclination distance between the pillars is 5m, and the slope length is 40~60m. It is divided into three mining areas of east, middle and west according to natural conditions. By 1972, the mining situation is listed in Table 1.

Table 1 Mining situation of tin mines in southern mines

In order to protect the surface, the old goaf was filled with waste rock in the Western District before 1965, and a small amount of new empty space was filled with waste rock in the central part, while the goaf in the eastern area was not treated.

Due to the long-term existence of a large number of goafs in the east and central regions, the upper part of the western area has been filled, but with the expansion of the lower mining area, the ground pressure has gradually increased. From 1965 to 1971, large-scale ground pressure activities occurred in three areas. (Table 2).

Table 2 Ground pressure activities of tin mines in South Mine

The obvious phenomenon during the period of earth pressure activity is firstly the sound of the rock formation, called “rock sound”, the loud sound (such as the bombing) is the deep layer and fault of the rock formation, and the small sound (such as firecracker sound) indicates that the shallow rock is damaged by the pressure. . The sound is extended from the deep to the shallow and the pillar, and the frequency increases from low to high. A few days before the big fall, the sound of the sound increased sharply, and more than 70 times per minute on the eve of the fall. Stope case of roof and pillar layers bearing damage hair ring, continuous, large caving indicating imminent.

The second phenomenon of ground pressure activity is that the top plate of the stope is loose and falling off. The top plate of the stope in the middle area is in the first three months before the big fall, and the number of falling blocks is 1.5-6 times/hour. Before approaching the big fall It increased to 15 to 17 times per hour in about 10 days; on the eve of the big fall, it increased dramatically to 27 to 30 times per hour.

The destruction of the pillar is an important basis for causing the roof to fall. According to the actual investigation of 84 pillars in 21 stopries in the central area, it was found that at the first month before the big fall, the pillars with cracks and spalling accounted for 12% of the total; the cracks and spalling were more, and the supporting capacity was weakened. Accounted for 28.5%; cracks staggered, exfoliation of more than 1/3 of the loss of support capacity accounted for 59.5%. As the pressure of the pillar increases, the bottom drum and cracking appear in the floor of the stope.

At the same time as the pillar collapses, the roof of the stope sinks, cracks and partially falls. According to the actual measured data, the average sinking speed of the roof in the middle area of ​​the three months before the big fall (October 1965) was 0.3-0.5mm/d, but it was 3~ on the eve of the big fall (late December 1965). 5mm / d, up to 7mm / d. Before the fall of the Eastern District, 128 plots were surveyed, and 69 occurred in different degrees.

The roadway near the stope and the roadway arranged under the pillar, cracking and serious damage.

At the same time as the large area of ​​the well fell, the ground cracked and sank, forming a surface subsidence basin, and there was a development process over time. The surface subsidence period in the central area is about one year, while the eastern area is as long as 7 to 8 years. The surface subsidence in the central and eastern regions is shown in Table 3.

Table 3 Surface cracking and sinking in the Middle East

When the underground falls, the landing area expands year by year, causing the ground pressure in the lower mining stage to increase, making the mining work difficult and the ore recovery rate decreasing. Before the big fall, the average recovery rate of 51 ore blocks in the 5th stage of the Eastern District was above 75%. However, after the formation of the caving area, when the mining stage of the lower 7 stages is recovered, the recovery rate is reduced to 50% to 60%. There are similar situations in the two regions of China and the West.

    Second, the characteristics of the ground pressure in the mining and mining method

Jiangxi tungsten mine has a mining history of 50 to 60 years. Since the 1960s, 31 large-scale ground pressure activities have occurred in 10 mining areas of 9 tungsten mines such as Dajishan and Pangushan. The ground pressure activity of the Pangushan tungsten mine is a representative example.

Pangushan tungsten based high-temperature gasification - hydrothermal fissure filling type deposit tungsten, bismuth, from the south, middle and north group consisting of veins, mineralized area of 1.2km ^2, three groups of veins with surface away from the 220m, 250m. Among them, the southern group has the largest scale, with 66 veins, mainly 19, with a strike length of 1350m, a depth of 800-1000m, a pulse width of 250-300m, an average pulse thickness of 0.35m, a tendency to SW, and an inclination of 85°.

The ore body is a quartz vein. The surrounding rock is mainly composed of quartz sandstone and metamorphic sandstone, which is hard and brittle. The geological structure of the mining area is relatively complex, and the faults are most developed after mineralization, and can be divided into four groups according to the occurrence, and the NEE is most developed to the fault. The joints are also very developed. There are five interpenetrating veins in the mining area.

The mine is mined using shallow hole retention. The length of the mine is 50-60m, the height is 42-70m, the top column is 2~3m thick, and the bottom column is 2.5~3m high, leaving no column.

Before the ground pressure activity, the depth of mining was 260-320 m, and the total area of ​​the goaf was 1.789 million (m) ³ . No treatment was done.

The first rock mass movement occurred on June 29, 1966, mainly between the stages 899 and 831, but had little effect on the 831 stage, and the upper 970 stage had little effect. Before the ground pressure activity, the pavilion fell off the stone, the lower roadway support in the lower part of the stope was broken, the piece was helped, and the rock wall was peeled off. During the ground pressure activity, the sound of cracking and breaking of the rock can be heard in the 899 stage, and the thunder of the friction when the rock body moves.

After the first rock movement, there were many ground pressure activities in the six stages, such as the closeness of the roadway, the breakage of the cross bracing, the crushing of the bottom column, the collapse of the wall, and the leakage of the floor.

The second large-scale rock movement occurred on September 24, 1967, affecting 696 to 1012 m6 stages, all of which suffered varying degrees of damage. Within a few hours, the tens of thousands of meters of roadway sank, 57% of the stope fell, the surface cracked and collapsed (Figure 1), the maximum crack width of 0.8m, the collapse area of ​​80,000 (m) ² , resulting in resource losses The value reached 24.8 million yuan. From 1967 to 1970, the production capacity decreased by 45% for four consecutive years, and the direct economic loss of enterprises was 7.35 million yuan.

Figure 1 Photograph of surface cracking and collapse

The basic characteristics of the geotechnical activities of the tungsten deposits in Jiangxi are that the veins of the veins along the weak geological structure face the slip of the goaf and collapse of the wall. The large-scale weak surface cuts the rock mass, destroying the continuity of the rock mass and reducing the stability of the rock mass. The size of the goaf is expanding with the mining work, and the stability of the rock mass is more vulnerable. The ratio of the empty solid is large, and the thinner the wall is, the easier it is to collapse. The top and bottom columns are subjected to unidirectional pressure on the upper and lower plates, resulting in stress concentration and being easily crushed or slipped along the weak surface. If there is water, it will reduce the strength of the fractured rock mass.

    Third, the stage of the mining method

Angang Gongchangling iron ore over 50 years of mining history, is a metamorphosed sedimentary deposits, through several tectonic movement, the deposit is extremely complex geological structure, ore body fault, joint development, the stability of the rock mass destruction great. There are many types of faults, including strike faults, lateral faults and horizontal faults.

The mine is above -100m level and has used horizontal stratified dry filling method and retention method. Because the filling body is not connected, and the lower part is mined by the retention method, some of the filling and destroying pillars in the upper stop are released, and there are empty areas that have not been treated by the retention method. According to statistics, there are a total of 920,000 (m). ³ empty areas.

From 1956 to 1969, a total of five large-scale ground pressure activities occurred in the mine. The basic conditions of previous ground pressure activities are shown in Table 4.

Table 4 Large-scale ground pressure activities of Gongchangling Iron Mine

After the first ground pressure event, the production was interrupted for half a year, and the No. 1 blind shaft was scrapped due to the destruction of the surrounding rock at the Tianlun. The first and second ground pressure activities lost a total of 11.6 million tons of ore. In the fourth ground pressure activity, a 200kW main fan and all the plants on the surface fell into the empty area, causing nearly 200,000 yuan of damage and destroying the underground ventilation system. The fifth geo-pressure activity was caused by the collapse of the wall between the two layers of Fe4 and Fe6, which caused the backstage to stop production for one month in the 60m phase and the loss of 200,000 tons.

During each ground pressure event, the underground stope and the roadway showed severe noise and rock falling, the column and top column were fractured, the roadway produced continuous cracks, the track was skewed, the roadway flakes, some died and could not enter, and the water Ditching and other phenomena. The surface produces cracks that run parallel to the ore body. As the mining depth increases, the rock on the upper plate expands intermittently, the surface sinks in a stepped manner, and the crack at the end of the ore body tends to close.

After observation, the main crack of the upper plate increased from 300m to 410m in 1972, the maximum width increased from 1.5 to 2.5m, the depth was 21m, and the step height difference was 1m. In 1978, the length was 500m, the width was 4m, the depth was 30m, and the step was high. The difference is 1.2 to 1.5 m. Outside the crack zone, there is no obvious deformation on the surface. The maximum sinking point of the surface subsidence curve is located on the upper plate of the near ore body. With the increase of the sinking value, its relative position is basically unchanged (Fig. 2).

Figure 2 The sinking curve of the Gongchangling iron ore surface

Observation line a-2; observation line b-1

The actual survey and long-term observations show that the basic laws of the movement of the Gongchangling iron ore deposit are:

1. When the continuous area of ​​the empty area is not large, the rock mass of the upper plate is soft and damaged by the structure, the rock mass of the upper plate develops from deformation to fall, and expands upward in the form of a falling arch, and some of them surface the surface to form a collapse funnel. And then expand to the surrounding; but some also fall to a certain height and then stop.

2. When there is a large continuous empty area, the surrounding rock stability is poor and the structural damage is serious. The rock layer expands along the structural weak surface intermittently upward and downward, and the surface cracks and forms the following sinking steps. The cracks in the upper and lower discs generally develop along the ore body, and the cracks at the end of the ore body tend to close.

3. When mining parallel steeply inclined thick ore bodies, because the thickness of the wall is thin (5-10 m), the wall collapses while the rock moves, which is similar to the mining of the steeply inclined ore body group.