Mineral rock properties from the perspective of mine geological safety

Mine geological work is an indispensable basic technical work in mining. It refers to the geological work directly for production in the production area or mining area of ​​the deposit in the mining process, according to the needs of the mine work. The geological work of the mine geological work Based on the project of mine mining activities, it is the technical basis and basis for mining production and management activities. The mining activities must be moved with the advancement of mining operations. There is no fixed working space and place, and the working environment conditions are greatly affected by engineering geology and hydrogeological conditions. Therefore, in order to ensure the smooth progress of mining activities, it is necessary to understand the impact of mine geological structure, hydrogeology and rock properties on mine safety.

First, the physical and mechanical properties of rock

The physical and mechanical properties of rock are closely related to mining work, which affects the choice of mining methods, the deployment of mining engineering and the use of blasting. Among them, some properties are often related to the safety of mining work. The physical and mechanical properties of rock mainly include rock elasticity, plasticity, brittleness, hardness, toughness, strength, bulk density, specific gravity, crushing property and characteristic impedance.

    (1) Elasticity, plasticity and brittleness of rock

Elasticity refers to the rock that is subjected to an external force and restores its original shape and volume after removing the external force. Rocks with high elasticity are not easily broken during rock blasting. Plasticity refers to the property that the rock deforms without being broken after the external force is released. Such as water-containing clay or argillaceous limestone, it is easy to make the blasthole mine large when blasting, and the blasting effect is poor. Brittleness refers to the property of cracking when the rock is deformed with little force. The greater the brittleness of the rock, the easier it is to be broken by the blast.

   (2) Rock hardness and toughness

The hardness of a rock is the ability of a rock to resist the invasion of foreign objects. Rocks with high hardness tend to be brittle, so they are easy to blast. Toughness, also called dynamic hardness, refers to the property of rock to resist the external force to maintain the overall state. Its size is related to the organization and structure of the rock, and the rock with high toughness is difficult to drill.

    (three) the strength of the rock

The strength of the rock is the ultimate stress value at which the intact rock begins to be destroyed. In blasting engineering, the rock is mainly subjected to impact loads, and the strength is only one aspect to illustrate the robustness of the rock. Due to the different nature of the force, the strength of the rock is divided into three types: compressive strength, tensile strength and shear strength. Common rock has a compressive strength of between 200 and 300 kg/cm 2 and between 2000 and 3000 kg/cm 2 . The tensile strength of the rock is 1/10 to 1/50 of the compressive strength, and the shear strength is 1/8 to 1/12 of the compressive strength. Therefore, the rock is afraid of pulling and not afraid of pressure. In the roadway or stope, and when the open slope is too steep or forms an umbrella rock, the rock mass is in a stretched or sheared state, which is prone to collapse and rock mass collapse.

    (4) The specific gravity and bulk density of the rock

The specific gravity of a rock refers to the mass of a dense rock (excluding pores) per unit volume, and the bulk density is the mass of a single volume of rock (including pores) per unit volume. The size of rock bulk density is related to the composition, density, void size and water content of the rock. The capacity of the rock has a greater impact on blasting, especially throwing blasting. The larger the bulk density, the more explosives are required. [next]

    (5) Porosity of rock

The porosity of a rock refers to the ratio of the volume of the hollow pores of the rock mass to the volume of the rock, which is usually expressed as a percentage. Rock formations with large porosity often contain more water, so pay attention to water and drainage work.

    (6) The swell of rock

The bulging property refers to the property that the volume of the rock is larger than that of the original rock after the rock is broken. The degree of fragmentation is usually expressed by the coefficient of expansion (or looseness factor) K:

K= V 2 / V 1

Where V 1 is the volume of the original rock before breaking, m 3 ;

V 2 - the volume of the broken rock, m 3 .

Generally, the hard and dense rock has a larger coefficient of expansion than the soft rock. The coefficient of expansion of several types of rock is shown in Table 3.

Table 3: The coefficient of expansion of several rocks
Rock type
Pure sand and gravel
Sandy clay
Medium hard rock
Hard rock
Fragmentation coefficient K
1.05~1.2
1.2 to 1.25
1.3 to 1.5
1.5 to 2.5
  

In the excavation and mining work, the fullness of the rock should be fully considered. For example, in order to accommodate rock with increased volume after crushing, sufficient space is required; on the contrary, in order to improve the blasting effect, the blasting space can be appropriately reduced to form an extrusion blast.

    (7) Characteristic impedance of rock

The product of the density of the rock and the velocity of the longitudinal wave propagating in the rock is called the characteristic impedance of the rock. The magnitude of the characteristic impedance reflects the resistance of the rock mass to the wave, so it is also called the wave impedance. Experiments show that the characteristic impedance of the explosive is closer to the characteristic of the rock, and the more energy is transmitted to the rock when the explosive is exploded, the better the blasting effect. The characteristic impedance of air is much smaller than the characteristic impedance of rocks and explosives. Therefore, when explosive energy is transferred from the explosive to the air and then transmitted to the rock, the energy loss is extremely serious, which requires compensation when selecting the explosive structure. .

Second, the rock's robustness and stability

(1) Ruggedness of rock

The ruggedness of rock is a comprehensive manifestation of rock's resistance to various physical and mechanical capabilities. Different rocks have different sturdiness. The same type of rock has a firmness coefficient due to its structure, structure and degree of weathering. The common rock solidity coefficient is between 0.3 and 20, which is divided into ten levels, as shown in Table 4.

Table 4 Platts rock solidity coefficient classification table
grade
Ruggedness
Rock type
f
I
The strongest rock
The strongest, dense and resilient quartzite , basalt and a variety of other particularly strong rocks
20
II
Very strong rock
Very sturdy granitic rock, quartz porphyry, very hard granite , siliceous schist, less hard quartzite than the upper one, hardest sandstone and limestone
15
III
Sturdy rock
Granite (dense) and granitic rocks, very rugged sandstone and limestone, quartz vein ore, solid conglomerate, very hard iron ore
10
IIIa
Sturdy rock
Limestone (sturdy), unsturdy granite, sturdy sandstone, strong marble and dolomite , pyrite
8
IV
Rough rock
General sand mine, iron ore
6
IVa
Rough rock
Sand shale , shale sandstone
5
V
Medium rock
Sturdy clay rock, unsound sandstone and limestone
4
Va
Medium rock
Various shale (not strong), dense marl
3
VI
Very weak rock
Weak shale, very soft limestone, chalk, rock salt, gypsum frozen soil, anthracite, normal marl, crushed sandstone, gravel, cement, hardened clay
2
VIa
Very weak rock
Crushed soil, broken shale, condensed gravel and gravel, hard coal, hardened clay
1.5
VII
Weak rock
Clay (dense), weak bituminous coal, strong impact layer clay soil
1.0
VIIa
Weak rock
Light sandy clay, loess, gravel
0.8
VIII
Earthy rock
Humus soil, peat, light sandy soil, wet sand
0.6
IX
Loose rock
Sand, hawthorn accumulation, fine gravel, loose soil, coal used
0.5
X
Sandy rock
Sand drift, swamp soil, watery loess and other water-bearing soil
0.3
   

   (2) The stability of the ore rock

Stability refers to the ability of the ore-rockable space to allow for the size of the exposed area and the length of exposure. The factors affecting the stability of the ore are very complicated. It is not only related to the composition, structure, structure, joint condition, weathering degree and hydrogeological conditions of the ore, but also related to the actual conditions formed by the mining process (such as the direction and shape of the roadway, Mining depth, etc.). Stability and firmness are both related and different. Generally, in the joint development and structural fracture zone, the rock fracture is good, but its stability is greatly reduced. To determine the stability of a rock, the structure of the rock mass must first be considered. The rock mass structure has several types: integral structure, block structure, layer structure, fragmentation structure and loose structure: [next]

The ore is divided into extremely stable, stable, moderately stable, unstable, and unstable five grades according to its stability:

1. Extremely unstable It is not allowed to have exposed area when digging into the roadway or opening up the stope. Otherwise, it may cause a phenomenon of topping. When tunneling, it is necessary to carry out maintenance for maintenance.

2. Unstable In this type of ore rock, a small unsupported exposure space is allowed, and the generally allowed exposed area is within 50 m 2 .

3. Medium stability means that the exposed area without support is 50~200m2.

4. Stable: It means that the exposed area without support is 200-800m2.

5, extremely stable: refers to the exposed area of ​​more than 800m2.

The stability of the ore rock is of great significance for the correct selection of mining methods in mining engineering and the reasonable determination of mine engineering support, maintenance and construction design. The stability of the surrounding rock of the ore body is closely related to the safe production of the mine. The stability of the roof of the stope depends mainly on two factors: lithology and formation pressure. When the lithology of the roof is soft and the pressure of the rock is large, it is prone to accidents. If the surrounding rock is relatively stable and the rock formation pressure is not large, it is not easy to rupture and fall. Therefore, before mining and roadway mining and face excavation, it is necessary to find out the stability of surrounding rock and to understand the pressure of rock formation in order to provide a basis for safe production of mines. When excavating in the roadway, the rock is encountered in softness, joint development, and there are many faults and fractures. When there is a broken belt, it must be supported in time to prevent accidents.

3. Physical and chemical properties of ore

(1) Radioactivity The content of radioactive elements in the earth is very small, but it is widely distributed, and it is concentrated in the granite in the upper part of the earth's crust, and gradually decreases toward the center of the earth. Earth mainly contains radioactive uranium, thorium, radium, in addition, potassium, rubidium, samarium, also with a radioisotope, radon and its daughters, when the dose exceeds the allowable value, also affect human health.

(2) Oxidation and naturalness Oxidation of ore refers to the property of sulfide ore to undergo oxidation-reduction reaction under the action of water and air to become oxidized ore. When the sulfur content of high-sulfur ore is above 18% to 20%, it is self-igniting and will be oxidized when stored on the ground or underground for too long. The sulphide ore is oxidized in the air and emits heat. If the heat is not good, after a certain period of time, the ore temperature will rise and spontaneous combustion will occur, causing an internal fire.

(3) Harmful substances Dust is floating in the air during mining, and some of the dust is harmful to the human body. The harm of dust to the human body depends not only on its chemical composition, but also on the mineral composition, particle shape and particle size of the dust. For example, the dust that causes pneumoconiosis depends not only on the content of silicon, but also on whether silicon is free silica (quartz, etc.) or other silicate minerals. The main cause of silicosis is free oxidation. silicon. Arsenic, mercury and other metals can cause poisoning. In the mining process, some gases that are harmful to the human body, such as strontium and its daughters SO 2 , CO, CH 4 , H 2 S, etc., may also be escaping.

In the production process of the mine, the above-mentioned harmful substances should be investigated to take appropriate protective measures to protect the health of workers.

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