• Geotechnical Engineering
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• v.14 no.3
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• pp.95-108
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• 1998

Downhole testing and seismic CPT (SCPT) have been widely used to evaluate stiffness profiles of the subgrade. Advantages of downhole testing and SCPT such as low cost, easy operation and a simple seismic source have got these testings more frequently adopted in site investigation. For the automated analysis of downhole testing and SCPT, the concept of interval measurements has been practiced. In this paper. a new inversion procedure to deal tilth the interval measurements for the automated downhole testing and SCPT (including a newlydeveloped continuous SCPT) is proposed. The forward modeling in the new inversion procedure incorporates ray path theory based on Snell's law. The formulation for the inversion analysis is derived from the maximum likelihood approach, which estimates the maximum likelihood of obtaining a particular travel time from a source to a receiver. Verification of the new inversion procedure was performed with numerical simulations of SCPT using synthesized profiles. The results of the inversion analyses performed for the synthetic data show that the new inversion analysis is a valid procedure which enhances Va profiles determined by downhole testing and SCPT.

• Journal of the Korean Geotechnical Society
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• v.23 no.11
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• pp.27-37
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• 2007

Downhole seismic method is very economic and easy to operate because it uses only one borehole and simple surface source to obtain the shear wave velocity profile of a site. In this study, automatic shear wave source was developed for efficient downhole seismic testing. This source is motor-spring type and easy to control. It can lessen the labor of operator and the working time. Moreover, it can provide better and repetitive signals for data interpretation. By combining developed automatic source with automatic receiver system, PC based data acquisition system, advanced managing program, and semi-automatic downhole performing system were constructed. Through comparison test with manual source, advantages of automatic source were verified. Constructed semi-automatic downhole testing system including automatic shear wave source was applied to the soft soil site. The applicability and reliability were verified and the importance of automating testing system for obtaining reliable result was emphasized.

• Journal of the Korean Geotechnical Society
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• v.23 no.4
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• pp.133-147
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• 2007

Downhole seismic method is very economic and easy of operation because it uses only one borehole and simple surface source to obtain the shear wave velocity ($V_s$) profile of a site. Even though it is widely used by the site investigation companies, universities and institutes, however, the $V_s$ profile determined by downhole seismic method has often low reliability due to employment of wrong combinations of field losing equipment and interpretation method and deficiency of experience. Round robin test was performed and testing equipment and procedure were compared. Adequate downhole seismic testing equipment was constructed based on the comparison and verification study of the round robin test. The data acquisition and software interpretation were also developed for automation and quick test in field. Finally, the effectiveness and applicability were verified through the field test by using the constructed testing system.

• Corrosion Science and Technology
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• v.7 no.1
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• pp.13-15
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• 2008

Aiming at the corrosion circumstances and corrosion prevention needs of downhole oil tubes, series protective coatings for downhole oil tubes have been developed in the authors' laboratory, including a baked type coating YG-01 and an air curing type coating YG-03, etc. The performance investigation of the coatings has been done for testing their corrosion resistance, mainly including salt fog test, immersion test in oil-field waste water and various acid solutions, high temperature and high pressure test in alkali solution or $H_2S/CO_2$ environment, as well as some other performances. The investigation results show that oil tube anti-corrosion coatings developed here can endure over 4000 hrs salt fog test, over 1000 hrs immersion in various acid solutions at room temperature and in boiling oil-field waste water. In addition, the coatings can keep intact after experiencing test in alkali solution under 70 MPa pressure at $150^{\circ}C$ for 24 hrs, and in simulative sour gas environment under the total pressure of 32 MPa ($P_{H_{2}S}=3.2MPa$, $P_{CO_{2}}=3.2MPa$) at $90^{\circ}C$ for 168 hrs, which show that the coatings can be used for corrosion prevention in downhole environments with specific high temperature and high pressure, such as sour gas wells. The other testing results show the oil tube protective coatings have excellent comprehensive performance.

• The Journal of Engineering Geology
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• v.20 no.2
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• pp.213-220
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• 2010

The permeability characterization on the natural barrier for deep geological disposal of radioactive waste is very critical to evaluate total safety and performance assessment of disposal site. However, the confidence level in using previous hydraulic testing equipments consist of simple components to estimate rock mass permeability is not high enough to reflect in situ condition. The purpose of this research is to establish an advanced hydraulic testing equipment, which is applicable to deep borehole (up to 1,000 m), through the improvement of technical problems of previous packer systems. Especially, the straddle packer hydraulic testing equipment was designed to adopt both the hydraulic downhole shut-in valve(H-DHSIV) to minimize the wellbore storage effect and the real time data acquisition system to measure the pressure changes of test interval including its upper and lower parts. The results from this research lead to not only improve current technical level in the field of hydraulic testing but also provide important information to radioactive waste disposal technology development and site characterization project.

• Tunnel and Underground Space
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• v.28 no.3
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• pp.258-276
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• 2018

The accurate and quantitative ground information on the hydraulic conductivity characteristics of rock mass is one of the key factors for evaluation of the hydro-geological behaviour of rock mass around an excavated opening under high water pressure. For tunnel and rock structures in seabed, where the sea acts as an infinite source of water, its importance become greater with increasing construction depth below sea level. In this study, to improve the problems related with poor system configuration and incorrect data acquisition of previous hydraulic packer testing equipment, we newly developed an integrated main frame and 30 bar level waterproof downhole sonde apparatus, which were optimized for deep hydraulic packer test in seabed rock mass. Integration of individual test equipment into one frame allows safe and efficient field testing work on a narrow offshore drilling platform. For the integrated type main frame, it is possible to make precise stepwise control of downhole net injection pressure at intervals of $2.0kg_f/cm^2$ or less with dual hydraulic oil volume controller. To ensure the system performance and the operational stability of the prototype mainframe and downhole sonde apparatus, the field feasibility tests were completed in two research boreholes, and using the developed apparatus, the REV(Representative Elementary Volume) scale deep hydraulic packer tests were successfully carried out at a borehole located in the basalt region, Jeju. In this paper, the characteristics of the new testing apparatus are briefly introduced and also some results from the laboratory and in-situ performance tests are shown.

• The Journal of Engineering Geology
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• v.11 no.1
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• pp.25-35
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• 2001

For the ground resrxmse analysis, both in-situ and laboratory testing techniques such as downhole, SASW, resonant column and torsional shear tests were perlormed for Hong-Seong area. The grOlmd upper 30m is classified as SD since it has an average shear wave velocity as 209m/s. The response specLrums obtained by site-specific analyses generally satisfied the seismic code, but near the resonance period the motion was evaluated to be higher than the code.

• Geophysics and Geophysical Exploration
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• v.2 no.4
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• pp.174-179
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• 1999

Shear wave velocity, one of major elastic constants in the dynamic design for civil structures, is conventionally measured from downhole, crosshole or sonic logging tests. SASW (Spectral Analysis of Surface Waves) method, which overcomes the disadvantage of the in-hole tests, can evaluate subsurface stiffness nondestructively and nonintrusively through measuring surface waves on surface. In this paper, principles of the SASW method are briefly described and the results of various field tests, conducted to investigate the applicability of the method, are summarized. The SASW method was successfully applied in evaluating the effects of dynamic compaction at Inchon international airport site, applied in evaluating the integrity of the lining and sidewall at a testing tunnel located in Mabukri, and applied in detecting thickness of a concrete retaining wall. The results of field tests and the nondestructive and economical characteristics of the method show the promising future of the SASW method in civil engineering projects.

• Journal of the Korean Geotechnical Society
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• v.19 no.3
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• pp.23-31
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• 2003

Over the past half century, borehole seismic surveys have been diversified into the three techniques such as crosshole, downhole, and suspension logging according to their devices and testing configurations. These field techniques have been improved, in terms of equipment and testing procedures, and are very valuable in the evaluation of ground characteristics for geotechnical and earthquake engineering problems. Yet, despite the importance and significance of the techniques as engineering tools, the techniques are not much used as standard penetration test (SPT) by practicing engineers. The possible explanations are cost and operational difficulties of the surveys as well as sophistication and complexity of the devices. An in-hole seismic method has been developed to meet the requirement of economical testing cost and practicality in engineering practice to measure dynamic soil properties. The prototype in-hole probe developed herein is small and light enough to be fit in three-inch boreholes and to be handled with bare hands. The performance of the source has been evaluated through extensive crosshole tests at various sites. The in-hole seismic method was adopted at three test sites and verified by comparing with crosshole results.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.442-451
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• 2008

The evaluation of field degree of consolidation on soft clays has been an important problem in geotechnical areas. Monitoring either settlements or pore water pressures has been widely applied in the filed, but occasionally they have some problems. This study addresses the suggestion and application of another method for evaluating the degree of consolidation using shear wave velocities. A research site where soft clay layers were consolidated by surcharging loads was chosen. Laboratory tests were performed to determine the relation between shear wave velocity and effective stress. Field seismic tests were conducted several times during the consolidation of the clay layers. The tests results show that the shear wave velocity increased significantly as clays consolidated. The shear wave velocities at each field stress states were derived from the laboratory results and the degree of consolidation was evaluated by comparing the shear wave velocities obtained by laboratory and field seismic methods. In most stress states, the degree of consolidation evaluated using the shear wave velocity matched well with that obtained from field settlement record, showing the potential of applying the method using shear waves in the evaluation of field degree of consolidation on soft clay deposits.