Waveform features and failure patterns of hollow cylindrical sandstone specimens under repetitive impact and triaxial co
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ORIGINAL ARTICLE
Waveform features and failure patterns of hollow cylindrical sandstone specimens under repetitive impact and triaxial confinements Shiming Wang . Yunsi Liu . Kun Du . Jian Zhou . Manoj Khandelwal
Received: 20 July 2020 / Accepted: 22 September 2020 Ó Springer Nature Switzerland AG 2020
Abstract In underground engineering practice, the surrounding rocks are subjected to a nonuniform stress field with various radial gradients. In this study, a series of conventional triaxial repetitive impact tests using hollow cylindrical sandstone (HOS) specimens were conducted to reveal the impact waveform features and failure properties of rocks under nonuniform stress conditions. The tests were conducted using a modified large diameter split Hopkinson pressure bar testing system. The confining pressure was set as 5, 10 and 12 MPa. The data of specimens under equilibrium stress states were chosen and analyzed, and the results
showed that more applied numbers of cyclic impact loads were needed to break rocks with the increase of confining pressure. Three types of cracks, i.e., ringshaped cracks around the hole in the center of specimens, axial cracks located in the outer cylindrical surface, and lateral cracks fracturing rock fragments into small pieces appeared in HOS specimens. The failure degrees of HOS specimens could be judged by the waveform features of the reflected wave, and the waveform features of reflected wave are similar in the same failure mode, regardless of the impact velocity and the number of impacts, which only affect the failure degree.
S. Wang Y. Liu School of Civil Engineering, Hunan University of Science and Technology, Xiangtan 411201, Hunan, China e-mail: [email protected]
Keywords Hollow cylindrical sandstone Confining pressure Repetitive impact loads Reflected waveform Ring-shaped crack
Y. Liu e-mail: [email protected] K. Du (&) J. Zhou (&) School of Resources and Safety Engineering, Central South University, Changsha 410083, Hunan, China e-mail: [email protected] J. Zhou e-mail: [email protected] M. Khandelwal School of Engineering, Information Technology and Physical Sciences, Federation University Australia, Ballarat, Australia e-mail: [email protected]; [email protected]
1 Article Highlights 1. The failure mode of the specimen under confining pressure during repetitive impacts can be judged by the waveform of the reflected wave in the triaxial SHPB test. 2. The impact velocity and the number of impacts will affect the degree of damage but have no effect on the failure mode.
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3. It is found that there are stretching and compression zones in the radial direction of hollow cylindrical specimens according to elastic mechanics analysis, and the zonal disintegration phenomenon will occur when using cyclic impact on sandstone under radial gradient stress.
2 Introduction The surrounding rocks near to the boundaries of underground excavation spaces are mainly under
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