Consideration on setting of detonation time interval of control blast

摘要

In NATM tunnel construction, Noise, low frequency sound, vibration propagates to the surroundings by blasting excavation. Although these are instantaneous phenomena of several seconds a day, they have a large influence on neighboring houses, therefore, countermeasures are often used. In the problem of blasting vibrations, countermeasures are taken by control blasting to change that increase the number of detonations, but it is known that a high reduction effect can be exerted particularly by using an electronic delay detonator. Normally excavation is carried out by detonation of about 100 holes per 10 steps using an electric detonator. In the case of using an electronic delay detonator excellent in accuracy of control of time intervals, since it detonates in one hole per step, the influence of ground vibration can be suppressed by reducing the amount of explosive per step. In recent years, electronic delay detonators that can set and change the explosion time interval have been developed according to site geology such as ground geology and rock quality of vibration propagation routes. In this report, test blasting using an electronic delay detonator capable of changing the detonation time interval at the site was carried out, and the effect and control blasting utilization method were examined. From the results of test blasting, it has been shown that more effective vibration reduction is possible by setting the detonation time interval of the electronic detonator according to the ground surface hardness in the vicinity of the maintenance target and the geological condition of the propagation route. Furthermore, in order to improve the vibration reduction effect, we grasp that it is important to grasp the dominant frequency in the maintenance target and the propagation route. Therefore, we examined the method of grasping the dominant frequency and discussed the method of determining the detonation time interval and the method of determining the optimum range of application of control blast.