Cutting blasting is the key to the blasting excavation of rock tunnel, and the main factors influencing the blasting effect are the cutting method and blasting parameters. Cutting blasting is a physical and chemical process of rock and explosive, which is accompanied by high temperature, high pressure and high strain. There are four main factors influencing the blasting effect of cut blasting: explosive properties, rock properties, cutting blasting parameters and construction technology.
These four factors are interrelated, mutual influence and mutual restriction. In the design of cutting blasting, first of all, according to the actual rock properties of the blasting site, it is appropriate to choose appropriate explosives and determine the reasonable cutting blasting parameters, and choose the correct construction technology, which can achieve a more ideal cut blasting effect.
Rock properties
It is generally believed that the failure of rock under explosion is the result of the interaction of stress wave and explosion gas expansion. According to wave impedance of rock, the rock is divided into three categories: rock with low wave impedance and rock with medium wave impedance and rock with high wave impedance.
It is considered that the peak value of stress wave is different when the rock is damaged with different wave impedance. For the rock with high wave impedance, the rock failure is mainly caused by the stress wave generated by the explosion of the explosive. For the rock with medium wave impedance, rock failure is due to the explosive stress wave and explosive gas expansion effect. For the low wave impedance rock, the expansion of the detonation gas plays an important role on the failure of rock.
On the other hand, the rock is a typical brittle material, and structural defects such as cracks, joint sand faults generally existed and its performance to structural defects is very sensitive, rock mass structure characteristics will seriously affect the cutting blasting effect. The structural defects in rock mass have positive effect on the crack propagation and extension. The stress concentration effect can be produced by the rock mass in the structure defect, which is beneficial to the rock fragmentation. The formation of rock burst fracture zone first appeared in the structural defects. However, if the structural defects in the rock mass is too much, it will cause the explosion of the premature escape of gas, resulting in energy loss. Due to the changeable geological condition in rock tunnel excavation blasting and rock properties are different, so in rock tunnel blasting design of coping rock properties to judge and measure, so as to select the appropriate cut blasting method and the construction technology.
Explosive properties
Rock blasting fragmentation mainly depends on the energy released by the explosive, the main parameters affecting the blasting effect are density, detonation and detonation velocity. In rock blasting, explosion pressure is greater, more intense damage to the rock and throwing action. The volume of detonation temperature, explosion and explosion gas has great influence on the explosion pressure. It is an effective way to improve the blasting effect by using the high density and the larger power of the explosive.
Another important parameter that affects the performance of the explosive is detonation velocity, and the explosive stress wave with different detonation velocity can be excited by different parameters in rock, which has important influence on the blasting effect. In the same case of the same explosive density and detonation heat, the higher the detonation velocity, the greater the peak stress wave generated in the rock, but the corresponding reduction in the time of action. Therefore, in rock blasting, rock crack growth and fracture is not only determined by the peak of the explosion stress wave, but also with the stress time, the stress wave shape and other factors. Therefore, in order to obtain better blasting results and reduce the consumption of explosives, the explosive used in the rock must be selected according to the rock properties. In general, high strength explosive are selected for high impedance rocks, and high explosive are selected for low wave impedance rocks.
Cut blasting parameters
Cutting blasting parameters are the key factors influencing the blasting effect. For different construction conditions and geological conditions of rock mass, different engineering survey and section size, the targeted design of blasting parameters is required. For the parallel hole cut blasting, according to the engineering experience summary there are three ways of cutting: cracks cutting, barrel cutting and the spiral slotting. Three cutting methods have their own advantages and disadvantages, which need to be selected according to the different engineering survey and rock properties. In addition, the design of blasting parameters includes explosive ratio, hole diameter, hole depth, hole spacing etc. The different parameters are interrelated and influence each other, so it is needed to determine the reasonable blasting parameters according to the actual situation to get a better effect.
Construction technology
With the development of blasting equipment and drilling tools, the influence of construction technology on the blasting effect is more and more important. parallel hole blasting has higher requirements on the accuracy of drilling, which requires drilling construction technicians have a higher professional standard. Due to the uneven level of drilling technical personnel, the quality of drilling is not satisfied with the requirements, this kind of situation often happens. In addition to the impact of the cutting effect of the construction process also includes supporting methods, base station structures, blasting hole blocking, etc. Selection of applicable construction equipment and scientific construction method is an important measure to ensure good cutting effect.
Reference
Fan, Xingjun. (2016). The analysis of improving effect of parallel hole cut blasting on the basis of test results. 10.2991/ifeesd-16.2016.62.
