A New Seismic Well Logging Technique and Its ... - Springer Link

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A new seismic well logging technique has been developed for identifying the damaged zone around the rock masses that was affected by the stability of rock ...
KSCE Journal of Civil Engineering (2011) 15(7):1177-1183 DOI 10.1007/s12205-011-1108-x

Geotechnical Engineering

www.springer.com/12205

A New Seismic Well Logging Technique and Its Application Seong-Seung Kang*, Atsuo Hirata**, Yuzo Obara***, and Chin-Surk Ko**** Received January 15, 2010/Revised September 7, 2010/Accepted January 30, 2011

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Abstract A new seismic well logging technique has been developed for identifying the damaged zone around the rock masses that was affected by the stability of rock structures due to excavation of underground. In this study, we firstly purpose to introduce a new seismic well logging technique, then to show the results of the examples applied on rock structures of open-pit limestone mine and an underground power station. Finally, we intend to verify its efficiency. A new seismic well logging technique consisted of trigger sensor, super-elastic probe and signal conditioner was found applicable to evaluate the state of rock mass. From the measured result of rock slope in an open-pit limestone mine due to blasting, we defined that it was able to quantitatively evaluate the extent of damages of rock structures as well as to determine the location of damaged zone. In addition, this technique can measure P- and Svelocities simultaneously. P-velocity measurement from an access tunnel closed underground power station was also successfully carried out for observing the state of rock mass. It is expected that the newly developed seismic well logging technique would be a useful method for evaluating the integrity of rock mass and for ensuring an efficient tunnel support members. Keywords: a new seismic well logging technique, damaged zone, stability of rock structures, super-elastic probe, P- and S-velocities ···································································································································································································································

1. Introduction Development of rock structures such as rock slope and tunnel, oil, gas and underground waste disposal storages, and underground power station is increasing with the year in our country. Ground survey using well logging methods such as downhole test, crosshole test, Vertical Seismic Profiling (VSP), and geotomography is usually performed in borehole (Sheriff, 1991). Also, this method is applied to obtain ground information. The well logging methods are mainly used in order to explore for oil and to survey for geological structures. Previous tools used for these purposes did not apply to survey an underground condition of a small scale because they are commonly with a large size (Balch and Lee, 1984, Hardage, 1992). Tools of a large size are inconvenient for handling in the field. Therefore a new survey method with a small size easily applicable to the field is desired. Out of this necessity, we developed a new seismic well logging technique, which is applicable to an investigation of rock mass state around tunnel or in rock slope and a damaged zone due to blasting (Kang et al., 2006). This technique is also possible to estimate behavior of rock structures, before and after support installed in rock mass (Hirata et al., 2003, 2005). In this study, we firstly purpose to introduce a new seismic well logging technique, then to show the results of some examples

applied on rock structures like rock slope stability of an open-pit limestone mine and the state of rock mass around underground power station. Finally, we intend to verify its applicability and efficiency.

2. A New Seismic Well Logging Technique 2.1 Seismic Refraction Method and Seismic Well Logging Method The principle of seismic refraction method is illustrated in Fig. 1(a). The underground structure is assumed to be consisted of two layers, L1 and L2 with different physical properties. If a velocity of the upper layer is faster than that of the lower layer (V1