• Journal of The Korean Society of Agricultural Engineers
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• v.47 no.7
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• pp.37-45
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• 2005

In this study, R/S analysis which was proposed by Mandelbrot & Wallis (1969) was applied to evaluate the presence of the fractal property in the cone tip resistance of in-situ CPT data. Hurst exponents (H) were evaluated in the range of 0.660$\sim$0.990 and the average was 0.875. It was confirmed that a cone tip resistance data had the characteristic of fractals and it was expected that cone tip resistance data sets are well approximated by a fBm process with an Hurst exponent near 0.875. It was also observed that the boundary between layers were obviously identified as a result of R/S analysis and it will be usage in practices.

• Journal of the Korean Geotechnical Society
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• v.24 no.12
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• pp.53-63
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• 2008

In this study, the cone tip resistances of cemented sand are measured by performing a series of miniature cone penetration tests in large calibration chamber, and the relations with constrained modulus, unconfined compressive strength, and shear strength of cemented sand are suggested. Experimental results show that both the cone tip resistance and constrained modulus of sand increase with increasing cementation effect as well as relative density and confining stress. However, it is observed that the relative density and confining stress have more significant influence on cone tip resistance than constrained modulus of cemented sand. Since the cone penetration into the ground induces the damage of cementation, the cone tip resistance can't properly reflect the cementation effect of sand. An analysis based on the constrained modulus shows that the measured cone tip resistance underestimates the deformation modulus of cemented sand by about $70{\sim}85%$. In addition, this study establishes various relationships among the above soil properties from the regression analysis.

• Journal of the Korean Geotechnical Society
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• v.25 no.10
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• pp.31-40
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• 2009

As the measurement of strain-gage type cone penetrometer is influenced by the temperature change during penetration, the temperature is a factor producing an error of the cone tip resistance. In this study, the 0.5 mm diameter temperature transducer and 7 mm diameter micro cone penetrometer are manufactured by using FBG sensors to evaluate the effect of temperature on the cone tip resistance. Design concepts include the cone configuration, sensor installation and the temperature compensation process. The test shows that the tip resistance measured by strain gauge is affected by the temperature change. The error of the tip resistance increases with an increase in temperature change, while the temperature effect on the tip resistance of FBG cone is effectively compensated by using FBG temperature transducer. Temperature compensated tip resistance of the strain gauge cone shows the good matched profile with FBG cone which performs real-time temperature compensation during penetration. This study demonstrates that the temperature compensation by using FBG sensor is an effective method to produce the more reliable cone tip resistance.

• Smart Structures and Systems
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• v.15 no.4
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• pp.1085-1101
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• 2015

Changes in substructure conditions, such as ballast fouling and subgrade settlement may cause the railway quality deterioration, including the differential geometry of the rails. The objective of this study is to develop and apply a hybrid cone penetrometer (HCP) to characterize the railway substructure. The HCP consists of an outer rod and an inner mini cone, which can dynamically and statically penetrate the ballast and the subgrade, respectively. An accelerometer and four strain gauges are installed at the head of the outer rod and four strain gauges are attached at the tip of the inner mini cone. In the ballast, the outer rod provides a dynamic cone penetration index (DCPI) and the corrected DCPI (CDCPI) with the energy transferred into the rod head. Then, the inner mini cone is pushed to estimate the strength of the subgrade from the cone tip resistance. Laboratory application tests are performed on the specimen, which is prepared with gravel and sandy soil. In addition, the HCP is applied in the field and compared with the standard dynamic cone penetration test. The results from the laboratory and the field tests show that the cone tip resistance is inversely proportional to the CDCPI. Furthermore, in the subgrade, the HCP produces a high-resolution profile of the cone tip resistance and a profile of the CDCPI in the ballast. This study suggests that the dynamic and static penetration tests using the HCP may be useful for characterizing the railway substructure.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.117-125
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• 2008

The detection of thin-layered soil is important in soft soils to evaluate the soil behavior. The smaller diameter cone penetrometer have been commonly used to detect the layer with increasing sensitivity. The objective of this study is to detect the thin-layered soil using cone resistance and electrical resistance. The cone resistivity penetration test (CRPT) is developed to evaluate the cone tip resistance and electrical resistance at the tip. The CRPT is a micro-cone which has a $0.78cm^2$ in projected area. The application test is conducted in a laboratory large-scale consolidometer (calibration chamber). The kaolinite, sand and water are mixed to make the specimen at the liquid limit of 46% using a slurry mixer. It takes two months for the consolidation of the specimen. After consolidation, the CRPT test is carried out. Furthermore the standard CPT results are compared with the electrical resistance measured at the tip in the field. This study suggests that the CRPT may be a useful tool for detecting thin-layers in soft soils.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.179-188
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• 2006

In this study, R/S analysis which was proposed by Mandelbrot & Wallis(1969) was applied to evaluate the presence of the fractal property in the cone tip resistance of in-situ CPT data. Hurst exponents(H) were evaluated in the range of $0.660\sim0.990$ and the average was 0.875. It was confirmed that a cone tip resistance data had the characteristic of fractals and it was expected that cone tip resistance data sets are well approximated by a fBm process with an Hurst exponent near 0.875. It was also observed that the boundary between layers were obviously identified as a result of R/S analysis and it will be usage in practices.

• Journal of the Korean Geotechnical Society
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• v.27 no.2
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• pp.43-52
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• 2011

The characteristics of shear zone in granular soils largely affect the stability of geo-structures. The goal of this study is to evaluate shear zone in a direct shear test using shear wave, electrical resistivity, and cone tip resistance. Bender elements and electrical resistivity probe are embedded into the wall of a direct shear box made of transparent acrylic material to estimate the shear wave velocities and the electrical resistivity at shear and non-shear zones. At the point of peak and residual strength, micro cone penetration test which can be available to measure tip resistance has been performed. Experimental results show that the shear wave velocities at upper shear zone increase during shearing while the values remain constant at bottom and lower shear zone. Also, resistivities at lower shear zone depend on relative density while resistivities at bottom remain constant. The results of cone penetration test demonstrate the correlation of the cone tip resistance and small strain shear modulus at shear zone. This study suggests that the application of the modified direct shear box including shear wave, electrical resistivity and the micro cone tip resistance may become effective tools for analyzing the characteristics of a shear zone.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.331-340
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• 2009

This study evaluates the relationship between cone tip resistance ($q_c$) and small-strain shear modulus ($G_{max}$) of cemented sand. For this purpose, a series of miniature cone penetration and bender element tests are performed in calibration chamber specimens with various gypsum contents. Experimental results show that both $q_c$ and $G_{max}$ of sand increase with increasing cementation level as well as relative density and vertical confining stress. However, the relative density and vertical confining stress has more significant influence on $G_{max}$ and $q_c$ of uncemented sand than those of cemented sand. It is observed that the $G_{max}/q_c$ ratio of cemented sand decreases with increasing relative density. This result means that state variables have more affect on $q_c$ than $G_{max}$ of cemented sand. Test results also show that the effect of vertical stress on $G_{max}-q_c$ relation is reduced by cementation effect.

• Geotechnical Engineering
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• v.6 no.4
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• pp.33-42
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• 1990

In the analysis of the static cone penetration resistance or the point resistance of end bearing piles, the vertical effective stress has been chosen as the reference stress. However many reported experimental results indicate that the cone tip resistance is dependent rather on the in -situ horzontal stress than the vertical effective stress. To clarify this point, published experimental results have been re-evaluated and the laboratory penetration tests have been performed. From the results it is concluded that the cone tip resistance is influenced by both the vertical effective stress and the horizontal effective stress. It is further concluded that the mean normal stress should be used as the reference stress in the analysis.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.1407-1414
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• 2009

In this study, a Jeju sand, which contains both siliceous and calcareous materials, was sampled from a beach in Jeju Island. It is observed that the Jeju sand has high extreme void ratios due to the angularity of grains and the intra-particle voids of hollow particles. From cone penetration test using calibration chamber system, it is found that the cone tip resistance($q_c$)-relative density(Dr)-vertical effective stress(${\sigma_v}'$) relation of Jeju sand almost matches to that of high compressible quartz sand. However, this correlation overestimates the relative density of a coastal sediments in Jeju Island maybe due to the cementation effect of this area. From analysis of the results of cone penetration and SPS tests at a coastal area in Jeju Island, it seems reasonable to assume that the coast of Jeju Island is a natural cemented sediments.