• 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.36 no.10
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• pp.57-71
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• 2020

Liquefaction-induced sand boils were observed during the Pohang earthquake (Moment magnitude, 5.4) on November 15, 2017, specifically in the region of agricultural fields and park areas near the epicenter. This was recorded as the first observed liquefaction phenomenon in Korea. This paper analyzes liquefaction potentials at the key sites at Pohang area. The simplified methods and current design standard were used to evaluate the occurrence of liquefaction. The seismic demand was estimated based on the NGA-WEST2 ground motion prediction equations (GMPEs). The liquefaction resistance of the ground was determined using the in-situ tests: standard penetration test (SPT) and cone penetration test (CPT). The liquefaction potentials were quantified by liquefaction potential index (LPI), which were compared with those from the previous studies.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.477-484
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• 2001

In this paper shows the evaluation of the liquefaction potential of soils using in situ test. There are different types of in situ test used in the evaluation the liquefaction potential. In the particular study the Standard penetration test(SPT), Cone penetration test(CPT), ad Seismic cone penetration test (SCPT) were used. The SPT N value has been used all over for a very long time. The evaluation of the liquefaction of soil was preformed using the worldwide renowned CPT and SCPT. Shake 91 program was used to evaluate the results obtained by different in situ test and were later analyzed.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1340-1352
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• 2008

In this study, S-wave velocity range is gauged in every field test method at the total 5 locations in the marine deposits in Incheon area. field test method is accomplished the SPT(Standard Penetration Test), CPT(Cone Penetration Test), SPS(Suspension PS Logger), SCPT (Seismic Cone Penetration Test) and so on. The S-wave velocity of SCPT in the downhole test method is measured lower than SPS logger at the N value > 15 range. But at the N value < 15 range, SPS logger and SCPT result is measured same. In this result, although the soil strength of the downhole test method increased, the rate of S-wave velocity is tend to be slowed. This result shows that the downhole test is difficult to apply at the place that the intensity of soil is more extreme and harder soil. And it shows that the existing Imai(1982) type that is mostly used within the country is not suitable for the marine deposits. Thus, the empirical formula that can show the range of S-wave velocity in each N value for domestic soil is needed.

• Journal of the Korean Geotechnical Society
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• v.33 no.5
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• pp.25-35
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• 2017

Liquefaction is one of the major seismic damage, and several methods have been developed to evaluate the possibility of liquefaction. Recently, a probabilistic approach has been studied to overcome the drawback of deterministic approaches, and to consider the uncertainties of soil properties. In this study, the spatial variability of cone penetration resistance was evaluated using CPT data from three locations having different variability characteristics to perform the probabilistic analysis considering the spatial variability of soil properties. Then the random fields of cone penetration resistance considering the spatial variability of each point were generated, and a probabilistic analysis of liquefaction induced settlement was carried out through CPT-based liquefaction evaluation method. As a result, the uncertainty of soil properties can be overestimated when the spatial variability is not considered, and significant probabilistic differences can occur up to about 30% depending on the allowable settlement.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.92-104
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• 2005

Over the past decade, major advances have occurred in both understanding and practice with regard to assessment and mitigation of hazard area associated with seismically induced soil liquefaction. In this paper, assessment of liquefaction resistance of soil are reviewed from the recent researches. In addition site characteristics investigation methods and tests for seismic design and liquefaction analysis are reviewed. Finally, introduction and characteristics of remedial measures against soil liquefaction are reviewed briefly.

• Journal of the Korean Geotechnical Society
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• v.22 no.5
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• pp.13-26
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• 2006

The purpose of this study is to examine the method of liquifaction potential occuring at the reclaimed land in Incheon district and to compare the result obtained by the method based on the earthquake of 6.5 magnitude. In addition, the effects of ground improvement and liquifaction potential were evaluated on the basis of SPT and CPT, which have been performed before and after the compaction pilot test. As a result, we realized that the bigger the energy of dynamic compaction test was, the better effect we got. After the dynamic compaction test, as the strength of ground increased, the safe factor also increased. It was evaluated that the method of dynamic compaction improved the seismic performance. Accordingly, the method of the quality control of reclaimed land based on dynamic compaction method was presented.

• Journal of the Korean Geotechnical Society
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• v.21 no.9
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• pp.65-75
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• 2005

Maximum shear modulus of soil is a principal parameter for the design of earth structures under static and dynamic loads. In this study, the statistical data of maximum shear moduli of silty sands in Songdo area in the west coast of Korea evaluated by various field and laboratory tests - standard penetration test (SPT), cone penetration test (CPT), self-boring pressuremeter test (SBPT), downhole test (DH), seismic cone penetration test (SCPT) and resonant column test (RC) were analyzed. Based on the measurement of shear moduli using DH which is known as maximum value at very small strain, the new empirical correlations between shear moduli and SPT or CPT values were proposed. Predictions of maximum shear moduli using the proposed correlations were compared with the data obtained from DH. The good agreement confirmed that the proposed correlations reasonably predicted the maximum shear moduli of silty sands in the area.

• Proceedings of the Korean Geotechical Society Conference
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• 2007.09a
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• pp.623-634
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• 2007

The aim of this research is development and verification of resistivity seismic dilatometer (RSDMT) system. The resistivity module for obtaining resistivity-depth plot and seismic module for obtaining wave velocity-depth plot are attached to the conventional flat dilatometer testing equipment. To enhance reliability and repeatability of seismic part in RSDMT, automatic testing system including automatic surface source, PC based data acquisition system and operating program were developed. To obtain real resistivity value of soil, geometric factor for the array of electrodes in RSDMT was derived empirically. The verification studies for the developed RSDMT system were performed at the southeast side of Korea where soil improvement work is planned. SPT, CPT, geophysical subsurface imaging techniques and some laboratory tests were performed for the comparisons. As one penetration of RSDMT, various soil parameters could be obtained. The results of field test showed good repeatability and reliability in every part. From these studies, developed RSDMT system was checked and the effectiveness of this system was verified in light of proper evaluation of geotechnical characteristics of soft soil.

• Journal of the Earthquake Engineering Society of Korea
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• v.24 no.5
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• pp.197-209
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• 2020

Evidence of liquefaction during the 2017 Pohang earthquake has highlighted the urgent need to evaluate the current seismic design standard for liquefaction in Korea, particularly the liquefaction triggering standard. With the simplified method, which is the most popular method for evaluating liquefaction triggering, the factor of safety for liquefaction triggering is calculated via the cyclic stress ratio (CSR) and the cyclic resistance ratio (CRR). The parameters in the CSR and CRR have undergone changes over time based on new research findings and lessons learned from liquefaction case-histories. Hence, the current design standard for liquefaction triggering evaluation in Korea should also reflect these changes to achieve seismic safety during future earthquakes. In this study, liquefaction susceptibility criteria were discussed initially and this was followed by a review of the current liquefaction triggering codes/guidelines in other countries and Korea. Next, the parameters associated with the CSR such as the maximum ground acceleration, stress reduction factor, magnitude scaling factor, and overburden correction factor were discussed in detail. Then, the evaluation of the CRR using the SPT N-value and CPT qc-value was elaborated along with overburden and clean-sand correction factors. Based on this review of liquefaction triggering evaluation standards, recommendations are made for improving the current seismic design standard related to liquefaction triggering in Korea.