INFLUENCE OF BLASTING ROUND ON EXCAVATION DAMAGED ZONE OF SURROUNDING ROCK
(1. School of Civil Engineering and Architecture,Anyang Normal University,Anyang,Henan 455000,China;2. State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences,Wuhan,Hubei 430071,China;3. School of Energy and Safety Engineering,Hunan University of Science and Technology,
Xiangtan,Hunan 411100,China)
Abstract:The variation in acoustic velocity along the borehole and the influence of blasting on excavation damaged zone(EDZ) are studied based on the in-situ testing results. It is found that the acoustic velocity increases gradually,then decreases gradually after a peak and tends to be stable finally. There are reinforced and weakened zones in survey area in each blasting round. Its distribution is complex and closely related to the size of EDZ and the effect of blasting. The cumulative effect of blasting rounds illustrates that the weaken zone lies in the crack area;and its damage is attributed to the effect of longitudinal wave and transverse wave. The reinforced zone lies in the stress concentration area;and its reinforcement is contributed to the tamping effect of blasting vibration and the compression of bulking force. When the distance between the borehole and the working face is up to a certain value,the blasting does not affect the shape of EDZ in spite of some slight adjustment in acoustic velocity. In other words,it does not cause the offsets of the stress concentration zone. Accordingly,the principle and time for EDZ test are proposed. Meanwhile,along the axis direction of the tunnel,the acoustic velocity tends to be stable when the testing point has a certain distance from the working face,which can provide a method to determine the blasting influence range. It is the determination of influence range that provides significant guidance for choosing the best time for the support of soft rock tunnel and the protection scope against rock burst of hard rock tunnel.
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