발파에 의한 근거리 지중진동의 예측방법에 관한 연구

Abstract

The rapid industrial development has brought material abundance to society. However, with it comes the problem of environmental pollution, which affects the society. The blasting works in the construction fields in particular have been held accountable for the high levels of noise and vibrations polluting the environment. The aforesaid problems have been institutionally managed through the environmental impact assessment until the completion of the works. Such institutions have made technological research possible for efficient blasting construction works and provided the opportunities for direct and indirect developments of the blasting technology. Previous blasting vibration analyses had been conducted to understand the properties of the vibrations comparatively far from the blast holes to establish the limits of the damage to the structures. However, the analysis have recently been expanded to near field vibrations in terms of assessing damage to rock mass around the blast holes. There are many methods to assess damage to rock mass. However, most of them are based on blasting vibration velocity and from assessing damage caused by vibration. In addition, near field vibration predictions have been based on far field vibration estimates. However, as target areas of blasting are reduced and targets are transferred to underground facilities, the importance of identifying underground vibration properties have been highlighted. Therefore, in respect to the properties of near distance vibration that indicate vibration properties within a few meters underground, few results from international research have been reported. As a result, it has been confirmed that properties of near distance vibration include very high frequency and larger scale vibration compared with that of near distance vibration. As for damping of energy according to distance, far distance has larger damping, although, the father the less damping. Indications show that spherical divergence effect is significant in near distance blasting, however, when focused upon; the effect of absorption is significant in far distance blasting. Until now, impact assessments have been conducted on structures using ground vibration, measured at the ground surface level in a broad area, despite no clear differentiation from the blast hole. Furthermore, to identify the properties of blasting vibration, near distance and far distance areas have been separately analyzed. Previous international studies such as the Holmberg model showed results of comparison, although, they did not provide evidence of the different methods used for prediction and assessment. Moreover, there had been no national research, owing to difficulties in choice of test and measuring equipment. The purpose of the following study is to present how to measure and predict near distance underground vibration. In addition, discuss the impact vibration has on underground structures rather than damage of rock mass, which were the methods used in previous studies. However, to demonstrate the results from the study we measured far distance vibration and predicted near underground vibration using the Holmberg model. Also, to theoretically induce predicting techniques we present an equation of prediction using values of physical properties from target rock mass as well as properties of explosives. In this study four kinds of explosives were used for measuring near distance vibration: ANFO, Dynamite, Emulsion and Finex. When focusing on vibration velocity and vibration acceleration, the following results were obtained: 4.28 , 58,619 for ANFO; 1.41 and 38,064 respectively for dynamite; 1.27 and 34,257 respectively for emulsion; and 0.92 and 28,195 for Finex. The frequency of each vibration ranged from 4,000 to 5,000 Hz. To assess the adequacy of sensors inserted underground we carried out two tests using Finex when blasting. In addition, we selected two types of fixed boards for the installation of sensors. As for ground surface vibration, steel boards were used, whereas, aluminum boards were used underground. Under the same conditions the variation in vibration was 35.4 - 37.3% with a deviation of 1.9%. Furthermore, the judgment of the placement of underground sensors proved appropriate. This study obtained C value using vibration value and distance measured as a result of test blasting and the amount of explosive. Then we obtained referring to physical properties of rock and properties of explosives as follows: 0.472, for ANFO, 0.550 for dynamites, 0.663 for emulsion, and1.453 for Finex. To compare the resultant values, the value of Finex was larger than that of other explosives. Here, defines the degree of transformation of explosive energy in blasting into elasticity energy. Therefore, as Finex was applied in terms of protection rather than damage of rock mass, its value was higher. In other words, its contribution to destruction of rock mass is lower than that of other explosives. Using the near distance prediction with a use of the Holmberg model and the prediction equation presented in this study, we compared the results. For the near distance, predicted value of vibration by the Holmberg was higher, and the farther, the higher predicted vibration. To compare adequacies between previous methods and the method presented, we examined damage area of rock mass. For the previous methods, critical distance of ANFO was 4.9 m and 3.7 m of emulsion. To obtain the critical distance with the method suggested in this study, that ANFO was 2.8 m, and 2.2 m of emulsion. To confirm the fractured zone of actual rock mass, we used BIPS for televiewer hole imaging. It was judged that the damage of rock mass that can be visually seen was within 2.1 ~ 2.2 m. As a result of examining damages roughly, the proposed method has higher adequacy than previous methods.