• Journal of the Korean Geotechnical Society
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• v.24 no.11
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• pp.133-141
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• 2008

In this study, a new method for estimating the undrained shear strength $s_u$ of saturated clays using piezocone penetration test (CPTu) result is proposed. This is to develop more effective CPTu-based $s_u$ estimation method at lower cost with less uncertainty. For this purpose, a marine clay deposit is selected and tested through extensive experimental testing program including both in-situ and fundamental laboratory tests. The proposed method is based on a correlation between the undrained shear strength $s_u$ and the cone resistance $q_t$, without introduction of the total overburden stress into the $s_u-q_t$ correlation. As a result, no additional testing procedure for collecting undisturbed soils samples is required, which can reduce overall testing cost. To verify the proposed method, 4 test sites, which consist of a variety of soil conditions, are selected and used for comparison between measured and predicted undrained shear strength. From comparison, it is seen that predicted values of $s_u$ using the proposed method match well those from measured results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2C
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• pp.95-103
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• 2008

Seismic piezocone penetration tests (SCPTu) can be used to obtain dynamic properties of soils as well as cone resistance and penetration pore pressure. However, the SCPTu system can be hardly utilized in marine soils because it is difficult to install the source apparatus which generates the shear wave in offshore site. The authors developed an inhole type piezocone penetration test (CPTu) equipment which both source and receiver composed of bender elements were installed inside the rod located behind the cone. Therefore, it can be applicable to even an offshore site without any additional source apparatus. The objective of this paper is to investigate the practical application of inhole type CPTu by performing laboratory model tests using kaolinite as soft clay. The shear wave velocities of kaolinite soil were measured with time, and the effects of soil disturbance due to the installation of source and receiver were also examined for various distance between source and receiver.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.979-986
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• 2008

In this study, it enforced DMT test, CPTu test, laboratory consolidation test, because it estimated stress history of Gwangyang port marine clay. Through DMT test obtained Horizontal stress index($K_D$), predicted overconsolidation ratio by $K_D$. To compare empirical equation with laboratory consolidation test and CPTu test calculated OCR examined application. The result, Powell & Uglow(1988) method underestimated OCR value in comparison with Suggestion. Comparatively Byeon wi yong(2004) and Chang(1991) method seem to exactly predict in-situ stress states. Sugawara(1988) method of CPTu test seems to underestimate OCR.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.09a
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• pp.125-153
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• 2005

It has been widely known that the seismic piezo-cone penetration test (SCPTU) is one of the most useful techniques for investigating the geotechnical characteristics including dynamic soil properties. As the practical applications in Korea, SCPTU was carried out at two sites in Busan and four sites in Incheon, which are mainly composed of alluvial or marine soil deposits. From the SCPTU waveform data obtained from the testing sites, the first arrival times of shear waves were and the corresponding time differences with depth were determined using the cross-over method, and the shear wave velocity profiles (VS) were derived based on the refracted ray path method based on Snell's law and similar to the trend of cone tip resistance (qt) profiles. In Incheon area, the testing depths of SCPTU were deeper than those of conventional down-hole seismic tests. Moreover, for the application of the conventional CPTU to earthquake engineering practices, the correlations between VS and CPTU data were deduced based on the SCPTU results. For the empirical evaluation of VS for all soils together with clays and sands which are classified unambiguously in this study by the soil behavior type classification Index (IC), the authors suggested the VS-CPTU data correlations expressed as a function of four parameters, qt, fs, $\sigma$, v0 and Bq, determined by multiple statistical regression modeling. Despite the incompatible strain levels of the down-hole seismic test during SCPTU and the conventional CPTU, it is shown that the VS-CPTU data correlations for all soils clays and sands suggested in this study is applicable to the preliminary estimation of VS for the Korean deposits and is more reliable than the previous correlations proposed by other researchers.

• Geophysics and Geophysical Exploration
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• v.9 no.3
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• pp.207-224
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• 2006

It has been widely known that the seismic piezo-cone penetration test (SCPTu) is one of the most useful techniques for investigating the geotechnical characteristics such as static and dynamic soil properties. As practical applications in Korea, SCPTu was carried out at two sites in Busan and four sites in Incheon, which are mainly composed of alluvial or marine soil deposits. From the SCPTu waveform data obtained from the testing sites, the first arrival times of shear waves and the corresponding time differences with depth were determined using the cross-over method, and the shear wave velocity $(V_S)$ profiles with depth were derived based on the refracted ray path method based on Snell's law. Comparing the determined $V_S$ profile with the cone tip resistance $(q_t)$ profile, both trends of profiles with depth were similar. For the application of the conventional CPTu to earthquake engineering practices, the correlations between $V_S$ and CPTu data were deduced based on the SCPTu results. For the empirical evaluation of $V_S$ for all soils together with clays and sands which are classified unambiguously in this study by the soil behavior type classification index $(I_C)$, the authors suggested the $V_S-CPTu$ data correlations expressed as a function of four parameters, $q_t,\;f_s,\;\sigma'_{v0}$ and $B_q$, determined by multiple statistical regression modeling. Despite the incompatible strain levels of the downhole seismic test during SCPTu and the conventional CPTu, it is shown that the $V_S-CPTu$ data correlations for all soils, clays and sands suggested in this study is applicable to the preliminary estimation of $V_S$ for the soil deposits at a part in Korea and is more reliable than the previous correlations proposed by other researchers.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.4
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• pp.1-13
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• 2009

Liquefaction is a significant threat to structures on loose saturated sandy soil deposits in the event of an earthquake, and can often cause catastrophic damage, economic loss, and loss of life. Nevertheless, the Korean peninsula has for a long time been recognized as a safe region with respect to the hazard of liquefaction, as the peninsula is located in a moderate seismicity region, and there have been no reports of liquefaction, with the exception of references in some historical documents. However, some earthquakes that have recently occurred in different parts of the world have led to liquefaction in non-plastic silty soils, a soil type that can be found in many of the western coastal areas of Korea. In this study, we first present procedures for evaluating the liquefaction potential, and calculate the liquefaction potential index (LPI) distribution at two western coastal sites using both piezocone penetration test (CPTu) data and standard penetration test (SPT) data. The LPI is computed by integrating liquefaction potential over a depth of 20m, and provides an estimate of liquefaction-related surface damage. In addition, we compared the LPI values obtained from CPTu and SPT, respectively. Our research found that the CRR values from CPTu were lower than those from the SPT, particularly in the range between 40 and 120 for the corrected tip resistance, (qc1N)CS, from the CPTu, or in the range of CRR less than 0.23, resulting in relatively high LPI values. Moreover, it was observed that the differences in the CRR between the two methods were relatively higher for soils with high fine contents.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.6
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• pp.523-531
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• 2008

In hole type CPTu equipment which combines the concepts of inhole test method and piezocone test method was newly developed in order to evaluate the dynamic properties of marine soils. It is possible to perform inhole type CPTu without any additional source device because the source and receiver are contained inside the cone rod, which is different from the conventional seismic cone system. In this study, laboratory tests using kaolinite as soft soil and numerical simulations using finite element method were carried out to investigate the effects of several parameters including test methods and soil conditions on the test results from inhole type CPTu and to find out the optimum test method. It was found that it is necessary to maintain the length of swing arm as well as the distance between source and receiver consistently to obtain the rigorous test results. The laboratory test and numerical results also reveal that contrary to the input wave frequency, the water content of soil layer and the disturbance due to the installation of swing arm apparently affect the shear wave velocity.

• Journal of the Korean Geosynthetics Society
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• v.16 no.1
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• pp.73-83
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• 2017

Laboratory and in-situ tests were conducted to evaluate the cone factors for the layers with low plasticity containing a lot of silty and sand soils from the west coast (Incheon, Hwaseong and Gunsan areas) and its applicability was evaluated based on these results. The cone factors were evaluated from 19 to 23 based on unconfined compression strengths (qu), from 13 to 13.8 based on simple CU strengths and from 11.6 to 13.1 based on field vane strengths, respectively. The unconfined compression strengths of undisturbed silty soil samples with low plasticity were considerably underestimated due to the change of in-situ residual effective stress during sampling. Half of unconfined compression strength (qu/2) based cone factors of silty soils with low plasticity fluctuated and were approximately 1.8 times higher than simple CU based values of these soils. When evaluating cone factors of these soils, it should be judged overall on the physical properties such as the grain size distribution and soil plasticity and on the fluctuation of the corrected cone resistance and the sleeve friction due to the distribution of sandseam in the ground including pore pressure parameter.

• Journal of the Korean GEO-environmental Society
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• v.9 no.2
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• pp.5-13
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• 2008

To identify the reclamation history formed by top dredged soil reclamation layer over the original ground, various field tests and laboratory tests were conducted. Especially when the original ground was not completely consolidated, CPTu test was carried out to calculate rational settlement due to the banking load. CPTu test results showed that the degree of consolidation of weak clay ground by dredged reclamation was on average 80%. As the research area was not completely consolidated by dredged reclamation in the past, the consolidation settlement should account for the residual settlement (20%) in the case of additional banking load. When the degree of consolidation of the original ground was not taken into account, the residual consolidation was expected in excessive settlement (up to 20%) and in such case PBD (Plastic Board Drain) was not effective in obtaining desired degree of consolidation.

• 지반과기술
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• v.3 no.1
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• pp.36-42
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• 2006