With the rapid economic development, increase of depleting resources and face a shallow mineral resources demand situation, many metal mine at home and abroad after another into the deep or ultra-deep mining state. According to incomplete statistics [1], by the 21st century, 1/2 of the open pit mines in China will be transferred to underground mining. At the same time, 2/3 of the underground mines will soon be transferred to deep mining or ultra-deep mining. For the complex conditions of deep rocks, the mining method using blasting caving ore will usher in new challenges. For example: how to carry out blasting in deep rock complex stress environment; how to control blasting to reduce the impact on stope stability; how to optimize blasting design to save energy and reduce emissions, to achieve high-quality blasting effect, to improve production effectiveness.
More than 100 metal mines with a depth of more than 1,000 kilometers have been mined abroad. The auTona gold mine in Witwatersrand, South Africa, was mined to 3,900 m underground in 2008, surpassing South Africa's 3,585 m EastRand gold mine [2]. The TauTona gold mine reached a depth of 3910m in 2009, making it the deepest mine in the world. Compared with many deep metal mines at home and abroad, although the depth of metal mining in China is still shallow, a large number of metal mines will soon enter deep mining. Such as Shandong Zhaoyuan Linglong Gold Mine, Yunnan Huize lead-zinc mine, Fankou Shaoguan, Guangdong, Hubei Ezhou Chengchao iron ore have entered the deep mining, Henan Lingbao Yin Xin gold mine shaft reached a depth of 1500m tunneling [ 3].
After entering the deep mining environment, it will face problems such as high ground stress, high temperature and high elevation. Whether the current mining methods and blasting methods are suitable for later deep mining, especially with the intelligent blasting and large-scale mechanized mining in the late deep mining. Due to the long-term high ground stress, the deep rock has great differences in its various characteristics compared with the shallow rock characteristics. In addition, the deep rock has mining dynamics such as rock burst, rock fall and instability. Phenomenon, if you can not choose the appropriate blasting method and control blasting energy, will increase these dynamic disasters.
1 The dynamic characteristics of deep blasting in hard rock are different due to their formation age and formation environment, different rocks and even the same rock layer. Due to the different bedding, joints and distribution of rock, the structure and mechanical properties of the rock are also very large. difference. Moreover, the deep hard rock is under the condition of high ground stress, and the environment is complex. The various characteristics of the rock and the properties of the shallow rock are quite different. The explosion of explosives in rock media is a very complicated process. At present, there is no complete and systematic theoretical analysis system and quantitative calculation basis, which also adds more difficulties to the study of deep rock blasting theory.
1.1 Properties of deep hard rock Due to the existence of high ground stress, hard rock in the shallow part is very common, and in the deep part, it may exhibit the characteristics of soft rock, which causes large deformation of the roadway and surrounding rock; most of the original rock in the shallow part In the elastic state, the deep original rock is in the state of “latent plasticity”, and the pressure and shear stress caused by the stress field of the original unequal pressure exceeds the rock strength, causing the potential damage state of the rock [4], and the deformation of the rock. Will change from brittle to ductile. This may be a “benefit” for rock blasting, but this “benefit” will provide opportunities for a series of dynamic disasters such as deep roadways and rock bursts.
Deep ground pressure usually has two forms: deformed ground pressure and impact ground pressure [5]. Deformed ground pressure is the pressure caused by the displacement of surrounding rock caused by excavation, which is also the most basic form of ground pressure. Impact rock pressure is a kind of rock dynamic phenomenon. It is a form in which a large number of elastic deformations in the surrounding rock can be suddenly released under certain incentives. The hard rock metal mine is called rock burst. Under deep high stress conditions, the surrounding rock has internal and external conditions that cause large deformation, which will cause microscopic or macroscopic rupture, rock formation movement, roadway floor, sheet gang, roof collapse, section shrinkage, bracket failure, stoppage, etc. The distribution of rock stress, restraining the deformation of surrounding rock and preventing the instability and destruction of surrounding rock, can reduce the mining dynamic disaster such as rockburst.
1.2 Blasting and control of deep hard rock Because the deep rock is in a complex environment, the blasting method used in shallow mining cannot be directly used for deep rock blasting, and the high ground stress of the rock must be fully considered. Blasting is carried out by high temperatures and various properties induced by rock. Moreover, it is necessary to consider the damage of surrounding rock caused by blasting, the derivation and expansion of various cracks, the rockburst caused by blasting vibration, and the instability of surrounding rock. The double effect of the mining system on the disturbance of the original rock (dynamic load) plus high ground stress makes the deep rock under dynamic and static combined stress [1].

The rock mass is a very complex, non-uniform, non-continuous geological body. The explosion effect in the rock mass is also quite complicated. Compared with the explosion in the deep rock mass, the explosion is more complicated, and the propagation and disturbance of the blasting seismic wave are very different. The initial in-situ stress in the deep rock mass can reach the order of magnitude compared with the uniaxial failure strength of the rock mass. When the rock mass has the initial geostress of the magnitude, the effect of the ground stress on the explosion effect in the rock mass, especially the damage More obvious. Studies have shown that even within the range of the strength of the rock mass, even if the initial magnitude of the initial stress is increased, the blasting fracture characteristics of the rock mass may be significantly changed. Therefore, under the condition of deep rock mass, the three-way explosion of the rock mass The damage effect can be reduced until the local pressure is large and the damage disappears [6].
The use of blasting ore is the most important mode of mining in hard rock metal mines. Therefore, blasting is often required in roadway driving and working faces. The rock mass is temporarily stabilized during the disturbance and balance process, while others are stable. Instability and other phenomena occur. The blasting vibration has the effect of vibration accumulation on the rock, which provides an energy basis for the teleportation and instability of the rock. To this end, it is necessary to study the various effects of blasting on deep hard rock mining.
2 Rockburst and dynamic disasters of deep hard rock prevention In the shallow mining of hard rock mines, the ground pressure and its hazards are generally controlled by means of support, caving surrounding rock, filling, etc., but in deep mining, the use of support The method of caving surrounding rock and filling is far from being able to solve the ground pressure and its hazards. In particular, some inducing factors caused by blasting make the rock mass have many uncertainties in time, space and energy, which ultimately leads to rockburst. A series of mining dynamic disasters such as instability of surrounding rock.
There are a large number of cracks and joints in the rock mass, which complicates the blasting of the rock mass. For deep rock mass blasting, the effect of controlling the deformation and failure process of the medium is first used to control the effect of the blasting. In the case of cracked and jointed explosion conditions, the deformation characteristics of the solid medium will cause additional fracture of the rock between the source and the fracture, and the collision of the additional failure with the static fracture will result in enhanced rock damage in the adjacent area of ​​the fracture, and long-term blasting makes The accumulation of space and energy in the original rock mass and the accumulation of vibration effects will lead to the sudden change of various properties of the rock mass, which will become the danger of unpreventable and measurable in deep mining. In the deep, the control of rock blasting is inextricably linked with the mining power disaster. If the blasting is well controlled, the probability of mining power disasters will be reduced a lot. Otherwise, the frequency of mining power disasters will remain high, not only seriously affecting Production will also bring huge losses to life and property. Therefore, controlling the blasting in the deep part of the hard rock is an important factor in preventing the mining power disaster.
2.1 The rockburst rockburst of deep hard rock is the sudden destruction of the rock mass (including fault slip) around the underground excavation space, accompanied by the rapid release of the strain energy of the compressed rock mass. The rockburst is often ejected by rock fragments. A large number of rock collapses or mineral shocks are manifested [7]. The vertical rock stress caused by gravity in the deep rock and some tectonic stress still exist in the rock during the tectonic movement, and the superposition of the two forms a high ground stress. The deep rock under the action of high ground stress is equivalent to applying some prestressing inside the rock, so that the deep hard rock becomes the energy storage body, that is, the deep original rock has the characteristics of energy source and energy sink. Under certain conditions, the rock accumulates. The deformation energy is released and turned into kinetic energy [8]. The implementation of blasting in the deep will provide opportunities for the rock to release energy, causing a series of disasters such as rockburst and surrounding rock instability.
Accumulation of vibrations generated by blasting in the deep, energy accumulation, induced joints, rock bursts, and instability of surrounding rocks are all issues of special concern. The combination of various inducing factors and the analysis of conditions will become the core problems to be solved in deep hard rock blasting. For the mechanism of rockburst occurrence, Professor Tao Zhenyu believes that a large amount of elastic strain energy accumulates inside the rock, and once it is subjected to mechanical shock or blasting power disturbance, it will suddenly be released to form a rockburst. Relevant statistics show that 2/3 of the mine rock explosion occurred after production blasting [9].
2.2 Causes and prevention of rockburst formation by deep blasting In deep mining, mine shock phenomena caused by various blasting are very common. For this reason, many mines have arranged micro-seismic detection systems to detect rockbursts and large mines, and obtained a large number of on-site data on dynamic disasters such as mines and rockbursts caused by blasting. A large amount of data indicates that there is a direct relationship between blasting and mine earthquakes, and blasting is one of the main inducing factors for mine earthquakes.
The blasting not only has the vibration accumulation effect on the rock, but also the energy accumulation effect. In a certain sense, the two can be mutually converted. As long as one of them meets the requirements of rock rupture, the rock can undergo a series of disasters such as rockburst, surrounding rock instability, and patchwork. The way to prevent rockburst is usually to use real-time monitoring of the microseismic monitoring system to assist in the prevention of rockburst. Faced with the impact of blasting on rockburst, it cannot be monitored and supported in a pure sense. It should be thoroughly understood in terms of its rock properties, joint development, fault slip, cleavage and destruction, and detailed safety measures should be formulated. The possibility of rock bursts caused by blasting is minimized. Mine support, caving surrounding rock, and other methods of controlling ground pressure can play an important role in the exploitation of deep hard rock. Although these methods can control the ground pressure, they cannot achieve a breakthrough in the prevention of dynamic disasters caused by rockburst and surrounding rock instability in deep or ultra-deep conditions. The deep hard rock rockburst support in foreign countries basically adopts shotcrete, anchor net and its joint support, or its development form, such as the anchor net and cable support of South Africa. Reasonable selection of mining methods, optimization of mining sequence, rational arrangement of well and road engineering, selection of section shape, selection of stope and roadway support methods are of great significance for preventing or mitigating rockburst disasters.
3 Hard rock deep blasting process and method discussion In the shallow mining of metal mines, the traditional house mining method divides the stage into mining room and pillar, first mining room and mining pillar, leaving a large number of pillars to support Surrounding rock, control the ground pressure activities, or after the completion of the mining, collapse the surrounding rock, fill the goaf, etc. to control the ground pressure. However, in deep mining, the pillars are subjected to a large static pressure, and the roof is settled quickly when the pillars are recovered in the later stage of mining, resulting in serious rockburst problems. Therefore, the use of conventional shallow mining methods in deep mining is quite inappropriate. Moreover, in the cutting, picking and mining processes of the roadway, it is necessary to destroy the rock by means of blasting to achieve the purpose of excavation and ore mining, but the blasting vibration generated by the blasting has produced stability to the completed roadway and the original rock mass. A great hazard, which is unavoidable during the mining process. At present, the research on continuous mining mode is still shallow, and there is still considerable dependence on blasting caving ore. It is necessary to include the impact of blasting on deep mining into the scope of research.

In deep blasting, in order to reduce the mining dynamic disaster caused by blasting, control the single mining amount in the mining process, reduce the collapsing step distance and the energy of blasting, the process of energy release of rock mass can be slowed down, and the rock mass can be dynamic. Balance provides time to effectively control a series of dynamic disasters such as rockburst or surrounding rock instability. In the shallow mining, the sublevel caving method without sill column adopts blasting and blasting, the stage height can reach 80-150m, the distance between the mining roadway and the step of collapsing can be greatly increased, and the diameter of the blasthole is also gradually increased. Then each time the mine falls, it will increase. However, in the deep mining, many properties of the rock have changed due to the presence of high ground stress. For this reason, only the energy and the amount of falling of a single blast can be controlled, and the step of the collapse can be reduced to balance the dynamic balance of the ground stress under complex conditions. At the same time, the frequency of mining power disasters caused by blasting is reduced. In deep mining, it is necessary to carry out restrictive corrections to the mining techniques such as the shallow field mining method, the filling mining method and the caving mining method before they can be applied to the mining, taking full account of the negative impact caused by the blasting.
In deep blasting, the conditions for blasting under high ground stress and high temperature conditions must be considered. For the adjustment and limitation of the pore network parameters, charge parameters, initiation parameters and explosive types used in blasting, and reasonable arrangement of the blasting method, comprehensive verification of indoor and field tests must be carried out. In the blasting process, the micro-difference control blasting is adopted, and the hole is detonated by the hole to reduce the release of the blasting explosive energy; the high-precision digital detonator is used to precisely control the differential time, and the frequency of the blasting vibration is reduced by the frequency shifting technique. The blasting vibration recorder is commonly used in the project to monitor and collect the blasting vibration, and then the blasting vibration signal processing is performed by wavelet transform time-frequency analysis method or HHT method. After the EMD is decomposed, each IMF component has different amplitude and frequency. By analyzing and processing each signal, adjusting the blasting parameters can reduce the impact of blasting vibration, and then control the blasting vibration-induced mining power. The probability of a disaster.

In deep blasting, for different rock and high geostress conditions, select the matching explosives to adjust the output structure of the explosive energy, reduce the earthquake caused by the ineffective energy consumption, and obtain the best blasting fracture and damage effect of the specific rock, so as to be effective The negative impact of controlled blasting. With the improvement of the explosive production process and the promotion of the use of mixed explosive vehicles, it is possible to properly adjust the explosive energy output of the mine according to needs. For example, in the mining process, the purpose of excavation and mining is different. The excavation is mainly the collapse of the surrounding rock into the lane, and the ore is the collapse of the ore. In the face of different rock masses, different explosives and blasting parameters are required to match. In order to achieve effective use of explosives, reduce earthquakes and disasters caused by ineffective energy consumption. In order to better understand the relationship between rock and explosives, dynamic experiments are needed to understand the various dynamic properties of rock.
4 Conclusion Deep mining and deep blasting are the development trend of metal mines. This paper analyzes the occurrence of deep hard rock, high ground stress, how to manage high ground stress by blasting, how to reduce mining dynamic disaster, the application of filling mining method in deep mining, blasting optimization, etc., and expounds deep mining and deep blasting. The problem. The mining dynamic disasters such as rock burst and roadway instability caused by blasting vibration are analyzed. By optimizing the blasting design, rationally controlling the ground pressure and reducing the occurrence of disasters, it can provide a safe environment for deep mining.


references:
[1] Goodman, Li Xibing. Modern metal deposit mining science and technology [M]. Beijing: Metallurgical Industry Press, 2006.
[2]TauTona AngloGold. SouthAfrica [EB/OL]. Http://miningTechnology. Com/projects/tautona_goldmine/.
[3] Wang Junqiang. Preliminary study on rockburst and occurrence mechanism of Yuxin gold deposit [J]. Mine Pressure and Roof Management, 2005 (4): 121-124.
[4] Li Xibing, Yao Jinrui, Gong Fengqiang. Dynamics in deep mining of hard rock metal mines [J]. Chinese Journal of Nonferrous Metals, 2011 (10).
[5] Guo Chao. Some key issues in deep mining of metal mines [J]. Industrial Technology, 2009.
[6] Qian Qihu, Wang Mingyang. Impact explosion effect in rock and soil [M]. Beijing: National Defence Industry Press, 2010: 74-75.
[7] Li Yulin, Sang Yufa, et al. Research on support of deep well hard rock rock burst roadway [J]. Journal of Rock Mechanics and Engineering, 1998(11).
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[9] Wang Xianneng, Huang Qiurun. Analysis of the influence of dynamic disturbance on rockburst [J]. Mountain Research, 1998, (16) 3: 188-192.


Author: Li Lin, Guolian Jun, Zhang Ning, Xu Hongbo; Liaoning University of Science and Technology, Liaoning Anshan 114000


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