An innovative application of borehole acoustic image and amplitude logs for geotechnical site investigation
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RESEARCH ARTICLE - HYDROLOGY
An innovative application of borehole acoustic image and amplitude logs for geotechnical site investigation Hsien‑Chang Kao1,2 · Po‑Yi Chou2 · Hung‑Chieh Lo2 Received: 7 June 2020 / Accepted: 25 September 2020 © Institute of Geophysics, Polish Academy of Sciences & Polish Academy of Sciences 2020
Abstract Down-hole acoustic televiewer (ATV logging) is a geophysical well-logging device known to be able to reveal underground in-depth image. However, reviewing the current developments in the area of geotechnical engineering, ATV logging data were predominantly used for the purpose of visualizing and calculating the specific structural features in an open borehole, and nothing more. Noticeably, to the majority of engineering applications, it appears that ATV logging played a minor role compared to other geophysical borehole logging tools. Our study does not take it for granted. A systematic study is presented of the significance and consequent applications of ATV logging. The significance of correlation between acoustic amplitude and different geotechnical parameters is discussed and found to be consistent with previous findings. The result tells that ATV logging is actually able to provide timely and ground-truth information during site characterization, if properly used. Additionally, in our study, a simple rock mass evaluation index, Aco-RQD, is proposed, which is applicable to all aspects of geotechnical engineering as long as the continuous ATV logging data are available. Keywords Acoustic image · Conductive fractures · Straddle-packer test · Geotechnical investigation
Introduction Receiving adequate and in-depth knowledge on the subsurface conditions at site is essential to many geological engineering practices. It means a systematic examination conducted by the professionals to obtain ground-truth data with down-hole exploration. Presently, a variety of advanced and exclusive down-hole techniques have been developed for practical use, and the choice can be made from a combination of electrical, nuclear, electromagnetic, seismic, thermal, fluid velocity, acoustic and optical image logging, and so on. Different principles and configurations associated with * Po‑Yi Chou [email protected] Hsien‑Chang Kao [email protected] Hung‑Chieh Lo [email protected] 1
Department of Civil Engineering, National Taiwan University, 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan
Geotechnical Engineering Research Center, Sinotech Engineering Consultants, Inc., 280, Xinhu 2nd Rd., Neihu Dist., Taipei 11494, Taiwan
2
specific objectives of investigation can be adopted. In order to cope with more extreme working environment, the development of more representative and reliability-based methods for down-hole characterization is needed. Down-hole image logging by acoustic televiewer (ATV), as its name implies, is based on analyzing the amplitude of the acoustic reflectivity from the water–solid boundary at the face of borehole (Deltombe and Schepers 2004) and generating an unwrap
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