Interpretation of rock blasting mechanism research and analysis

A large number of studies conducted by scholars at home and abroad pointed out that the fracture of fractured rock is the result of the interaction between the explosion shock wave and the explosive gas. However, compared with the uniform medium material blasting, the fracture of the rock mass is mainly the result of the explosion stress wave, and the fracture rock The explosion pressure of the explosive gas of the body is small, only when the stress wave breaks the rock into pieces, it plays the role of promoting the separation of the fragments; during the propagation of the stress wave in the fractured rock mass, the disturbance propagated between the cracks will be generated. New rupture; due to the limited development speed of the crack, the rate of the blast load has a greater effect on the growth of the crack, while the high strain rate load tends to produce more cracks.

On this basis, the current related research is mainly carried out in two aspects. First, the pursuit of general analytic calculation and analysis, the theoretical research aimed at establishing relevant computational models; first, combined with certain engineering practices, applicable to a certain range Experimental research on specific engineering design and parameter optimization. In terms of theoretical research, from the development history of rock fracture research, it can be divided into four stages: the elastic theory stage, the fracture theory stage, the damage theory stage and the fractal damage theory.

The elastic mechanics model considers rock as an isotropic homogeneous, continuous elastic body. The failure of rock under blast loading is caused by the maximum internal stress exceeding the rock stress limit. The rock is in an elastic state before breaking. This rationalization simplifies engineering problems, establishes mechanical models, and analyzes and calculates them. Since this theoretical model does not consider the material defects of rock, its theoretical basis and actual situation have a certain gap.

The fracture mechanics model considers that crack propagation and fracture failure in rock are the main factors affecting rock blasting fracture effect. Different from the elastic model, this model regards the rock as a brittle material containing microcracks. The process of rock cracking is the process of internal crack generation, expansion and fracture. However, the fracture mechanics model still regards the crack around as a uniform continuous medium, so it is only suitable for the fracture stage after macroscopic crack formation. The mechanical behavior and physical process between the material degradation and macroscopic crack formation are not analyzed. The scope of application is limited to the layered or sedimentary rocks that have been formed by macroscopic cracks.

In the study of rock blasting damage models, they believe that there are a large number of randomly distributed primary cracks in the rock. Under the blasting, some of the primary cracks will be activated and expanded, and the number of activated cracks will be exponentially distributed. They used the damage factor D to indicate the cracking and damage of these rocks. After the efforts of Seamen, Grady, Kipp, Kus, etc., finally, a two-dimensional numerical calculation model capable of simulating the dynamic crushing process of brittle rock was established by Throne and tested in oil shale blasting practice. These models use the assumption of crack activation to describe the generation and development of damage. It is considered that the material has cumulative damage under volumetric tension and the material stiffness is degraded. In the compressed state, the ideal elastoplastic constitutive model without damage is adopted. Therefore, the reasonable degree needs further study; at the same time, it is assumed that the crack density and strain obey the Weibull distribution, but the two material parameters k, m which determine the crack density distribution are difficult to determine, and thus its application is limited.

The domestic research on rock damage theory developed in the 1980s, mainly based on the theory of Grady et al., model correction, calculation and analysis for some specific problems, and some new calculation methods were discussed.

The damage mechanics model believes that the fracture of rock under blasting is the result of the activation and development of the original rock damage, and it is a step further to the fracture mechanics model.

However, there are still some problems in this theory. In addition to the computational difficulties, there are mainly the following shortcomings: First, the crack density method is used to solve the problem of determining the damage factor. The assumption of crack activation is adopted in the model, and the direct influence of natural damage such as cracks and holes existing in the rock on the blasting effect is neglected. The impact load acts on the rock containing the initial damage, which will have two effects: one is the deterioration of the material stiffness; the other is the dissipation of the stress wave energy. This reflects that the existence of the initial damage is conducive to the evolution and development of the dynamic damage of the rock (providing the source of the crack), and at the same time, the discontinuous surface of the particle interface, joints, bedding, etc. in the rock acts as a “quantity barrier” (dissipation) The energy acts as a barrier, so that the extended crack often ends here, and new cracks are only possible when more energy is supplied to the medium. The existing damage model only considers the decrease of rock equivalent modulus caused by the development of damage, but does not consider the factors such as the dissipation of energy caused by the evolution of damage, which leads to the phenomenon of local and actual inconsistency in numerical simulation calculation. In fact, when the strain rate is higher, the smaller the stress reduction region of the microcrack propagation, the more the number of cracks activated, that is, the higher the damage degree of the medium, and the greater the dissipation of the shock wave energy. Therefore, to establish a rock dynamic damage model, the energy dissipation problem accompanying the damage evolution process should be considered. Secondly, the damage and destruction of the rock by the explosive gas is not considered. In the actual situation, the micro-damage of the rock formation by the explosion stress wave will further develop under the action of the explosive gas, so the damage and damage of the rock by the explosive gas is not allowed. Neglect. The damage mechanics model is applicable to all kinds of rocks. Compared with the elastic model and the fracture model, it is more reasonable and practical in simulating rock properties. Although there are still some problems, it is still widely accepted and adopted in rock blasting theory research.

In the theoretical stage of fractal damage, it is pointed out that the various fracture structures of rock mass, whether it is fault or joint and micro-fracture, have a good statistical self-similarity in the distribution range or geometry within a certain range of measurement, and the fractal dimension can be used. To describe the complexity of its shape, and under the same measure change ratio, the fractal dimension can be used to quantitatively compare and analyze the fractures of different scales, and the fractal dimension is used to describe the inclination, inclination, orientation, etc. compared with the traditional ones. The parameters are more convenient to describe, more holographic, simple and straightforward, and have the advantage of being easy to substitute mathematical equations to construct new mathematical models. Between this, some scholars have introduced the concept of fractal geometry into the study of the dynamic characteristics of rock, and proposed a new rock blasting model using fractal theory. This type of model considers the various structural weak surfaces in the rock mass as the initial damage, the fractal dimension as the main parameter of the rock properties, and incorporates the damage and fractal into the thermodynamic framework, thus overcoming the previous model without considering the initial damage and Damage evolution is attributed to the lack of a volumetric strain function. At present, the widely accepted blasting theory relation model is mainly the damage model and the fractal damage model.

The fractal damage theory model introduces the concept of fractal geometry into the damage theory model, so that macroscopic weak surfaces such as joints and fissures can be reflected in the blasting model in the form of fractal dimension, considering not only the influence of rock original damage, but also the damage evolution process. The energy dissipation is linked, and the relationship between the fractal dimension and the fragmentation degree can be used to predict the blasting block. However, the fractal dimension calculation of the interior of the rock is still immature, and the experimental parameters of the fractal and energy dissipation of the damage process are not easy to obtain, which makes the application range of the model very limited. But as the research deepens, the model will be more widely used.

In terms of experimental research, domestic and foreign are mainly used to test the damage degree of rock mass under impact load such as explosion for the specific engineering problems, and try to establish the relevant rock failure law to guide the related follow-up work. . The main performances are as follows: Shi Wei et al. used a first-class light gas gun to carry out impact damage experiments on rock specimens, used soft recovery device to recover samples, and used sieving method to determine the composition of rock fragmentation after impact test, and analyzed the rock under different dynamic loads. Different block distributions are used to establish the distribution law of rock fragmentation under dynamic load. The experimental method has a certain guiding effect on the corresponding blasting design.

Lin Dayeng et al. studied the confining pressure effect of damage under rock cyclic impact load, simulated impact loading of marble specimen on pressure tester, tested the axial ultrasonic wave velocity of the specimen after impact, and described the variation of ultrasonic wave velocity. The degree of damage of the piece. The effects of confining pressure, load impulse and impact times on rock damage evolution are analyzed. The relationship between impact damage and impact times of marble under different confining pressures is obtained. The confining pressure effect of marble impact rock damage is analyzed. . The results show that the rock cyclic impact damage has obvious confining pressure effect, and the presence of confining pressure improves the rock's ability to resist impact damage. It is proved from the experimental point that the presence of high ground stress in deep mines has an important influence on the drilling efficiency of the borehole and the blasting efficiency of the rock in the initial stress field.

Yang Jun, Gao Wenxue, and Jin Ganwu explored the dynamic damage parameters of rocks and their evolutionary characterization methods to construct rock blasting damage models. Through rock impact damage experiments. The ultrasonic test was carried out on the test pieces before and after the impact, and the relationship between the dynamic damage of the rock and the attenuation law of the ultrasonic wave was obtained. Based on the acoustic attenuation law of rock impact damage process and its relationship with energy dissipation rate, a new rock blasting damage model is established. The calculation results of the model are verified by experiments and the numerical calculation of rock step blasting is realized.

Although the current experimental research is aimed at specific practical problems, if the experimental results can be combined with relevant theories, it will be of great help to reveal the mechanism of blasting and fracture of rock mass.

(II) Development trend In order to reveal the essence of blasting and fracture of jointed rock mass, people have adopted various methods and methods to carry out research. Among them, computer simulation has attracted more and more attention due to its special advantages. The key to computer simulation of rock mass blasting is to establish appropriate Blasting theory. The theory of damage mechanics and fractal theory of rock blasting are considered to represent the latest direction of rock blasting. Therefore, the development of rock blasting theory should be based on this. From the perspective of practical application, the existing blasting theory models have many shortcomings, which need to be further improved and improved. Improvements to existing blasting models are also a direction of blasting theory research. The mechanical response characteristics of rock under blasting are usually related to the basic elements of mesoscale such as voids, particles and matrix cracks.

The initial damage of the rock largely controls the rock breaking process, and the influence of the initial damage on the damage evolution process must be fully considered, which is neglected by many current blasting models. How to properly introduce the initial damage into the rock under the action of rock blasting is a similar accident with the explosion wave and the explosive gas (down to page 63), re-processing the new connection of the terminal and performing correct data analysis.

When a special command needs to be sent to the GPRS data transmission terminal, it is carried out through the module. For example, the server's IP address changes, the terminal's remote reset, and so on.

(4) Software Implementation Method In order to simplify the complexity of software design and avoid repeated development work, you can adopt the method of developing dynamic link library or ActiveX control. The essence of both is Windows dynamic link library DLL file. The dynamic link library is written in VB6.0 and contains the following main functions: (5) Conclusion The remote monitoring system based on GPRS network has been widely used in the field of industrial control. It frees people from cumbersome manual operations and concentrates on more detailed analysis and processing of field data. How to establish a communication system and obtain raw data is the basis for system establishment. This paper puts forward the basic idea of ​​GPRS communication software design, and solves several steps in software design. The method of establishing communication program by dynamic link library is obtained in multiple remote monitoring systems such as heat network management system and power meter reading system. Repeat the application.

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