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| Characteristics of shock load and initial stress unloading in blasting of compressed brittle medium |
| YAO Yingkang1,2, SUN Jinshan1, JIA Yongsheng2, WU Liang3, NI Mingliang1, MING Sheng1, CHEN Yang3 |
1.Engineering Faculty, China University of Geosciences, Wuhan 430074, China;
2.Hubei Key Laboratory of Blasting Engineering，Jianghan University, Wuhan 430056, China;
3.College of Science, Wuhan University of Science and Technology, Wuhan 430081, China |
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Abstract In order to study the blasting mechanism of brittle medium containing compress strain energy, the filed blasting experiments of the first-floor columns of high buildings were conducted, and the strain of the reserved part of the columns was monitored.The strain monitoring result shows that during the blasting process, when explosive in blasting hole is initiated, the time history curve of blasting load far from the blasting hole is approximately in the shape of triangle, and the strain rate in load increasing stage is higher than that in load decreasing stage.If the charge length is about 20 cm, the time of the explosion shock is about 1 ms.After the explosion shock wave disappears, the bearing capacity of the blasted medium can be maintained for several milliseconds after the detonation, because the moving speed of the fragment is much lower than the shock wave and the stress wave propagation speed.At this time, the medium is mainly affected by the explosive gas and the additional dynamic strain far from blasting holes is low.When the medium is completely destroyed, the fragments are thrown at a high initial velocity, and its bearing capacity disappears rapidly, then the initial strain rapidly releases to 0.The monitoring results show that the time history curve of strain relief is close to a straight line.The mechanical model of one-dimensional bar is deduced to analyze the explosion shock and initial stress relieving process.Through the superposition of the loading and unloading process of the straight bar in the time domain, the strain history of the reserved zone in the compression column blasting was simulated.The simulation of the blasting experiment shows that the initial stress began to unload after a few milliseconds of explosive shock.
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Received: 06 February 2018
Published: 15 December 2019
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