{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,2]],"date-time":"2026-06-02T15:56:04Z","timestamp":1780415764235,"version":"3.54.1"},"reference-count":27,"publisher":"MDPI AG","issue":"21","license":[{"start":{"date-parts":[[2020,10,24]],"date-time":"2020-10-24T00:00:00Z","timestamp":1603497600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100003565","name":"Ministry of Land, Infrastructure and Transport","doi-asserted-by":"publisher","award":["Grant 18TBIP-C144356-01"],"award-info":[{"award-number":["Grant 18TBIP-C144356-01"]}],"id":[{"id":"10.13039\/501100003565","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>The objective of this study is to develop a new vibration-free excavation method based on vermiculite expansion for rock cracking and to evaluate the performance of the heating system via elastic wave monitoring. Natural vermiculites expand rapidly in volume when heated above 800 \u00b0C. MgO powder is used to evenly transmit the surface temperature of a heater rod, which can attain high temperatures rapidly, to the vermiculites. The insertion direction of the heater rod greatly affects the expansion pressure. Three cuboid rock specimens are prepared and equipped with the heating system at different hole-to-face distances. Crack propagation is monitored by a pair of disk-shaped piezoelectric transducers. For short hole-to-face distances, the wave velocity and maximum amplitude rapidly decrease after certain time. For the greatest hole-to-face distance, the shear wave velocity remains constant during the test, while the maximum amplitude decreases after a certain time. The time taken for the velocity and amplitude of the shear waves to decrease reasonably corresponded to that taken for detectable crack propagation to occur on the surface of the rock specimen. The proposed method and materials may be useful from the viewpoints of rapid expansion, economy, and crack control.<\/jats:p>","DOI":"10.3390\/s20216054","type":"journal-article","created":{"date-parts":[[2020,10,26]],"date-time":"2020-10-26T03:51:47Z","timestamp":1603684307000},"page":"6054","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":6,"title":["Expansion-Induced Crack Propagation in Rocks Monitored by Using Piezoelectric Transducers"],"prefix":"10.3390","volume":"20","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-8610-2929","authenticated-orcid":false,"given":"Chi-Hyung","family":"Ahn","sequence":"first","affiliation":[{"name":"School of Electrical, Electronics and Communication Engineering, Korea University of Technology and Education, Cheonan-si 31253, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Dong-Ju","family":"Kim","sequence":"additional","affiliation":[{"name":"School of Agricultural Civil &amp; Bio-Industrial Engineering, Kyungpook National University, Daegu 41566, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yong-Hoon","family":"Byun","sequence":"additional","affiliation":[{"name":"School of Agricultural Civil &amp; Bio-Industrial Engineering, Kyungpook National University, Daegu 41566, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2020,10,24]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"449","DOI":"10.1007\/s00603-008-0016-y","article-title":"A numerical study on the screening of blast-induced waves for reducing ground vibration","volume":"42","author":"Park","year":"2009","journal-title":"Rock Mech. 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