• Journal of the Korean Geotechnical Society
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• v.30 no.8
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• pp.25-37
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• 2014

In load and resistance factor design (LRFD) method, resistance factors are typically calibrated using resistance bias factors obtained from either only the data within ${\pm}2{\sigma}$ or the data except the tail values of an assumed probability distribution to increase the reliability of the database. However, the data selection approach has a shortcoming that any low-quality data inadvertently included in the database may not be removed. In this study, a data quality evaluation method, developed based on the quality of static load test results, the engineering characteristics of in-situ soil, and the dimension of aggregate piers, is proposed for use in constructing database. For the evaluation of the method, a total 65 static load test results collected from various literatures, including static load test reports, were analyzed. Depending on the quality of the database, the comparison between bias factors, coefficients of variation, and resistance factors showed that uncertainty in estimating bias factors can be reduced by using the proposed data quality evaluation method when constructing database.

• Journal of the Korean Geotechnical Society
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• v.25 no.8
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• pp.5-21
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• 2009

Based on recent studies on rock socketed drilled shafts, it was found that the side resistance of rock socketed drilled shafts is affected by unconfined compressive strength of rock, socket roughness, rock types and joints, and initial normal stress. Especially, the socket roughness is affected by rock types and joints, drilling methods, and diameters. Since existing roughness measurement systems could be conducted only in the air, a new roughness measurement system, which can measure rock socket roughness in the air and also in the water, is needed. However, the development of new roughness measurement system fur civil engineers has been faced with difficulties of electrical applications. In this study, the laboratory verification system far BKS-LRPS (Backyoung-KyungSung Laser Roughness Profiling System) was developed, which can be applied both in the water and air. Based on the laboratory verification, it was found that the improved BKS-LRPS could define effective measurement distances for the conditions reflecting the apparatus and in-situ situations.

• Geotechnical Engineering
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• v.11 no.2
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• pp.29-36
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• 1995

Load testis are executed on model reticulated root piles (RRP) to figure out the optimum slanting angle in the piles installation. One set of model RRP consists of 8 slanting piles which are installed in circular patterns forming two concentric circles, each of which is made by 4 piles. Each pile which is a steel bar of 5m in diameter and 300mm in length is coated to become a pile of 6.5mm in diameter. The slanting angle of the model RRP varies from 0$^{\circ}$ to 20$^{\circ}$ Comparing ultimate bearing capacities of the model RRP of different installation angles, it is observed that the ultimate capacities of the RRP increase as the installation angle increases until 15$^{\circ}$, and the optimum slanting angle of the RRP is around 15$^{\circ}$ The ultimate bearing capacity of the 15$^{\circ}$-RRP is found to be 22% bigger than that of the vertical RRP and 120% bigger than that of the circular surface footing whose diameter is same with the circle formed by outer root piles'heads. However, it is noticed that when the slanting angle of the RRP is increased over 15$^{\circ}$, the ultimate capacity starts to be reduced. The ultimate capacity of 20$^{\circ}$-RRP is even smaller than that of the vertical RRP by as much as 5%. From the observation of the load settlement curve obtained during the RRP load tests, it is known that as the slanting angle gets bigger the load -settlement behavior becomes more ductile.

• Journal of the Korean Geosynthetics Society
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• v.18 no.4
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• pp.167-180
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• 2019

Friction piles are being constructed in Southeast Asia (Myanmar, Cambodia, Vietnam, etc.) where the soft ground is deep, and many cases of friction piles are accumulated in terms of experience. In this study, we used the results of four static load test and load transfer test conducted in Myanmar sites to analyze the skin friction of soil layer. In addition, we proposed a relationship chart with skin friction measured in the N-value of Standard Penetration Test (SPT) and the load transfer test result of the single drilled shaft. In the case of Myanmar sites, the range of soil layers was deeper than domestic sites, so the conventional formula of skin friction using the N-value of SPT is different from domestic sites. In sandy layer, fs = 0.096 N in Myanmar sites showed a similar result of the domestic fs = 0.106 N. In clayey layer, fs = 0.315 N, in Myanmar sites showed about 5.0 times higher than the domestic fs = 0.062 N. The results of this study are based on limited data. Therefore, if we analyze the results of more load transfer tests, we can suggest a conventional formula for skin friction according to the N-value. It is expected to be used as important basic data in the future.

• The Journal of Engineering Geology
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• v.19 no.4
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• pp.441-457
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• 2009

This study estimated ultimate load by the determination methods based on ultimate load, yield load and settlement using experimental data from static load tests that applied load to driven piles used in sandy grounds at home and overseas until failure appeared markedly. Estimated ultimate load was normalized with actually measured failure load, and was compared among the determination methods according to the characteristics of pile. In addition, I have identified to the determination methods suitable for estimating ultimate load, and reevaluated the safety factor when determining allowable load. From the results of this study were drawn conclusions as follows. Among ultimate loads estimated by the ultimate-load-based determination methods, the value interpreted by Chin's method tended to overestimate actual measurements, and B. Hansen 80% standard and the stability plot method were considered most reliable as their results were closest to actual measurements. According to the results of this study, in calculating the allowable load, if the safety factor to be applied to failing load obtained by the method of determining extreme load is converted to the safety factor applied to the Standards for Structure Foundation Design, a value larger than 3.0 should be applied except the B. Hansen 90% method, and a value larger than 2.0 should be applied in the methods of determining yield load. In addition, if the safety factor to be applied to load obtained by the settlement standard is converted based on safety factor 3.0 for extreme load, a value smaller than 3.0 should be applied to the total settlement standard and the net settlement standard.

• Journal of the Korean GEO-environmental Society
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• v.6 no.4
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• pp.59-64
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• 2005

Although high pressure discharge method is widely used for improving soft ground, it has various problems including lack of strength increase and the possibility of water pollution and soil contamination. MJM(Morta Jet Method) uses sand in addition to cement as the injection material. MJM uses triple rods with a built-in nozzle that allows easier discharge of the slime, resulting in higher replacement area ratio and more uniform formation of pillar hydrates, and thus results in significant increase in strength. MJM is expected to perform especially well as piles in marine clays. This study investigates the field applicability of the MJM through extensive laboratory and field tests.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.1
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• pp.163-170
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• 2007

To evaluate on the applicability of Chemical Compaction Pile (CCP) method to weak soil improvement, two kinds of testing chambers were fabricated and the changes of water content and shear stress associated with soil types, ages and distances from the center of pile were measured with different mixing proportions of CCP such as bottom ash, lime powder and added admixture. As results of test, it was noted that water content and shear stress of ground are mainly affected by the amount of lime powder and increase of the amount corresponds to rapid improvement of soil. And the improvement depended greatly on the types of soil also. It was finally found that CCP developed can be applicable to bearing pile as well as soil improvement since CCP has a bearing capacity enough to carry loads.

• Journal of the Korean GEO-environmental Society
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• v.13 no.2
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• pp.95-102
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• 2012

In this study, practical verifications for an advanced C.I.P(Cast in Place Pile) construction method were carried out. The structural characteristics of the method is to attach an angular joint in the steel-casing. This joint plays an important role in boring vertically, connected pile to pile, and protects the permeation of the ground water. For verifications, experimental research and numerical analysis were performed. In the experimental research, two model-tests were set up with the real scale steel-casing. One is to examine the leakage in the joint of piles and the other is to compare earth pressures in the front and the joint, respectively. In addition, 3 point bending test and compressive loading test were carried out and numerical analysis was performed to simulate the loading test. As a result of model-tests, the leakage in the pile joints was not shown up to 300 KPa of water pressure and stress concentration in the joint is out of the question. From the results of bending and compressive test, it was found that the new advanced C.I.P method is more convenient and superior than the conventional method.

• Journal of the Korean GEO-environmental Society
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• v.14 no.10
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• pp.11-16
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• 2013

Success or failure of the bi-directional pile load test for drilled shaft depends on point selection for loading cells, that is balanced location both uplift force and downward force. Methods to evaluate the ultimate unit side resistance in rockmass layer in both domestic and foreign are based on the uniaxial compression strength of rock core, which can hardly be obtained in domestic rockmass layers which are weathered rockmass layer and soft rockmass layer with very low RQD. Therefore, this study suggested the relation charts between the revised SPT N values and developed unit side resistance of each different layers, which were obtained from bi-directional pile load tests in various domestic sites. To evaluate the appropriateness of the relation charts, the developed unit side resistances from the relation charts were used to select the loading cell position and compared with the measured unit side resistances from field pile load test. Results showed that the developed side resistance from relation charts and the measured side resistance of weathered soil layer and weathered rock layer were very close. Average developed side resistance($1,325kN/m^2$), which are average of upper soft rock layer of loading device($1,151kN/m^2$) and lower($1,500kN/m^2$), was similar with the estimated value ($1,250kN/m^2$).

• Journal of Bio-Environment Control
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• v.30 no.4
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• pp.287-294
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• 2021

In order to expand facility agriculture and reduce greenhouse construction costs in reclaimed land, a greenhouse foundation method that satisfies economic feasibility and structural safety at the same time is required. As an alternative, the allowable bearing capacity and settlement were reviewed when the DCM(Deep cement mixing) method was applied among the soft ground reinforcement methods. To examine the applicability of the greenhouse foundation, the allowable bearing capacity and settlement were calculated by applying the theory of Terzaghi, Meyerhof, Hansen, and Schmertmann. In case of the diameter of 800mm and the width and length of the foundation of 4m, the allowable bearing capacity was 179kN/m² and the settlement was 7.25mm, which satisfies the required bearing capacity and settlement standards. The calculation results were verified through FEM(Finite element method) analysis using the Mohr-Coulomb material model. The allowable bearing capacity was 169kN/m² and the settlement was 2.52mm. The bearing capacity showed an error of 5.6% compared to calculated value, and the settlement showed and error of 65.4%. Through theoretical calculations and FEM analysis, it was confirmed that the allowable bearing capacity and settlement satisfies the design criteria as a greenhouse foundation when the width and length of the foundation were 4m. Based on the verified design values, it is expected to be able to present the foundation design criteria for greenhouses through empirical tests such as bearing capacity tests and long-term settlement monitoring.