• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.84-90
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• 2009

An integrity testing for stone columns was attempted using crosshole S-wave logging. The method is conceptionally quite similar to the crosshole sonic logging (CSL) for drilled piers. The critical difference in the logging is the use of s-wave rather than p-wave, which is used in CSL, because s-wave is the only wave sensing the stiffness of slower unbounded materials than water. An electro-mechanical source, which can generate reversed S-wave signals, was utilized in the logging. The stone column was delineated from the S-wave travel times across the stone column, and taking S-wave velocities of the crushed stone and surrounding soil into account. The volume calculated from the diametrical variance delineated is very close to the actual quantity of the stone filled.

• International Journal of Highway Engineering
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• v.12 no.4
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• pp.139-145
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• 2010

An integrity testing for stone columns was attempted using crosshole S-wave logging. The method is conceptionally quite similar to the crosshole sonic logging (CSL) for drilled piers. The critical difference in the logging is the use of S-wave rather than P-wave, which is used in CSL, because swave is the only wave sensing the stiffness of slower unbounded materials than water. An electro-mechanical source, which can generate reversed Swave signals, was utilized in the logging. The stone column was delineated using the S-wave travel times across the stone column, the S-wave velocity profile of the crushed stone($V_{cs}$-profile) and that of surrounding soil($V_s$-profile). In the calculation of $V_{cs}$-profile of the crushed stone, its friction angle and Ko (coefficient of lateral earth pressure at rest) are recommended to be used. The calculation of the column diameter is not much affected by the values of friction angle and Ko.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.03b
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• pp.317-324
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• 2000

In this study, ten drilled shafts were constructed for evaluating the application of NDT(Non-Destructive Testing) techniques. The drilled shafts, 0.4 m in diameter and 7.0 m in length, were constructed at Namyangju site in Namyangju City. One of the shafts was constructed with no defect, and the other shafts were constructed with the defects of soft bottom, necking, bulging, cave-in and/or weak concrete. Then, these techniques were applied to the bridge foundations for studying unknown bridge foundation characteristics.

• 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.

• Geophysics and Geophysical Exploration
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• v.9 no.3
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• pp.193-206
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• 2006

Among various borehole seismic testing techniques for determining body wave velocity, crosshole seismic method has been known as one of the most suitable technique for evaluating reliably geotechnical dynamic properties. In this study, to perform successfully the crosshole seismic test for rock as well as soil layers regardless of the groundwater level, multi-purposed spring-loaded source which impact horizontally a subsurface ground in vertical borehole was developed and applied at major facility sites in Korea. The geotechnical dynamic properties were evaluated by determining efficiently the body wave velocities such as shear wave velocity and compressional wave velocity from the horizontally impacted crosshole seismic tests at study sites, and were provided as the fundamental parameters for the seismic performance evaluation and seismic design of the target facilities.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1415-1426
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• 2008

Stone columns, locally called "GCP (granular compaction pile)" can be used to improve strength and resistance against lateral movement of a foundation soil like rigid piles and piers. Also installation of such a discrete column facilitates drainage, and densifies and reinforces the soil in the sense of ground improvement. The integrity of the GCP has been indirectly controlled with the records of each batch including depth and the quantity of stone filled. An integrity testing was attempted using crosshole S-wave logging. The method is conceptionally same as the crosshole sonic logging (CSL) for drilled piers. The only and critical difference is that S-wave should be used in the logging, because P-wave velocity of the stone column is less than that of ground water. The crosshole sonic logger does not have the capability to measure S-wave propagating through the skeleton of crushed stone. An electro-mechanical source, which can generate either P- or SH-waves, and a 1-D geophone were used to measure SH-waves. Two 76mm diameter cased boreholes were installed 1 meter apart across the nominal 700mm diameter stone column. At every 10cm of depth, shear wave was measured across the stone column. One more borehole was also installed 1 meter outward from the one of the above boreholes to measure the shear wave profile of the surrounding soil. The diametric variation of the stone column with respect to depth was evaluated from the shear wave arrival times across the stone column, and shear wave velocities of crushed stone and surrounding soil. The volume calculated with these variational diameters is very close to the actual quantity of the stone filled.

• Proceedings of the Korean Geotechical Society Conference
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• 1998.03a
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• pp.85-92
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• 1998

• Geotechnical Engineering
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• v.14 no.2
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• pp.67-78
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• 1998

Microtunnelling is a technique applied to install a small-size tunnel in a soft cohesionless ground. In microtunnelling, a series of concrete tubular segments are pushed from a starting pit to power-line tunnel under a runway of JFK international airport at New York. During the microtunneling process, bentonite is jetted with very hyh pressure through a nozzle to advance disturbance in the subgrade caused by the pressurized bentonite in the aspects of subgrade stiffness. SASW measurements were performed on the runway above the center line of the shear wave velocity profiles. Besides the change of subgrade stiffness, the change of subgrade strength was also evaluated by the site-specific relationships between shear wave velocity and N value, which was determined by N values. The estimated N values gave a clue to the understanding of the change of subgrade strength.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.119-126
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• 2008

Ground stiffness(shear wave velocity) is one of the key parameters in geotechnical earthquake engineering. An In-situ seismic technique has its own advantages and disadvantages over the others in stiffness measurements. By combining the crosshole and seismic cone techniques and utilizing favourable features of bender elements, a new hybrid probe has been developed in order to enhance data quality and easiness of testing. The basic structure of the probe, called "MudFork", is a fork composed of two blades, on each of which source and receiver bender elements were mounted respectively. To evaluate the disturbance caused by the penetration of the probe, shear wave velocity measurements were carried out in the Kaolinite slurry in the laboratory. Finally, the probe was penetrated in coastal mud near Incheon, Korea, using SPT(standard penetration test)rods pushed with a routine boring machine and shear wave velocity measurements were carried out. The results were verified with data from laboratory and cone testing. The performance of the probe turns out to be excellent in terms of data quality and testing convenience.

• 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.