• Journal of the Korean Geotechnical Society
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• v.28 no.10
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• pp.27-40
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• 2012

In the design of a piled raft, the axial resistance is offered by the raft and group piles acting on the same supporting ground soils. As a consequence, pile - soil - raft and pile - soil interactions, occurring by stress and displacement duplication with pile and raft loading conditions, act as a key element changing resistances of the raft and group piles. In this study, a series of centrifuge model tests have been performed to compare the axial behavior of group pile and raft with that of a piled raft (having 16 component piles with an array of $4{\times}4$) in sands with different relative densities. The test results revealed that the increase of settlement resistance occurs separately with settlement by group pile - soil interactions. The axial resistance of group piles (at piled raft) increases by group pile - raft (pile cap) interactions and that of raft (at piled raft) decreases by group pile - raft (pile cap) interactions.

• Journal of the Korean Geotechnical Society
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• v.36 no.7
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• pp.15-28
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• 2020

As the skin friction of an embedded pile is produced by the cement paste injected into the borehole, the skin friction cannot be evaluated by the end of initial driving test, which is conducted before the cement paste is cured. In addition, the total resistance of an embedded pile may not be properly evaluated during the restrike test if the base resistance is not fully mobilized because of the insufficient driven energy. The objective of this study is to suggest a new load-settlement curve of embedded piles by combining the results of the end of initial driving and restrike tests. Test piles are installed at fields by using the embedded pile method, and the results of the dynamic pile tests are analyzed using CAse Pile Wave Analysis Program (CAPWAP) after the end of initial driving and restrike tests are conducted. A new load transfer curve, which combines the behaviors of the pile base at the end of initial driving and of the pile shaft at the restrike, is suggested, and a new load-settlement curve is obtained. Subsequently, the resistances of the test piles are evaluated using the combined load-settlement curve, and compared with the results from the end of initial driving and restrike tests. The results showed that the resistances, which are evaluated using the combined load-settlement curve, may overcome the underestimation of the resistance because of the insufficient driven energy. In addition, the resistance resulted from the combined load-settlement curve may be more similar to that from the static load test because the suggested load transfer curve is closer to the behavior of the embedded pile compared to the results of end of initial driving and restrike tests. Therefore, this study demonstrates that the combined load-settlement curve may be effectively used for the evaluation of the bearing capacity of embedded piles.

• The Journal of Engineering Geology
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• v.16 no.1 s.47
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• pp.31-43
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• 2006

As a result of calculating bearing capacity of soft silt soil(ML) and soft silt soils(ML', SM, SM') mixed with sand, all kinds of soils showed smaller values than existing expressions and when theoretical values are applied, considerable review is required. It was found that ultimate surcharge(bearing capacity) of soft silt soil was $q_{ult}=1.34C_u$ that of ML' soil in soft silt soils mixed with 3 kinds of sand $q_{ult}=1.40s$, that of SM soil $q_{ult}=1.73s$ and that of SM' soil $q_{ult}=2.72s$, Consequently, as content of sand having greater permeability than silt soil in creased, soil was stabilized gradually.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5C
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• pp.343-350
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• 2006

The resistance bias factors for driven steel pipe piles are evaluated as a part of study to develop the LRFD(Load and Resistance Factor Design) for foundation structures in Korea. The 43 data sets of static load tests and soil property tests performed in the whole domestic area were collected and analyzed to determine the representative bearing capacities of the piles using various methods. Based on the statistical analysis of the data, the Davisson's criterion is proved to be the most reasonable method for estimation of pile bearing capacity among the methods used. The static bearing capacity formulas and the Meyerhof method using N values are applied to calculate the design bearing capacity of the piles. The resistance bias factors of the driven steel pipe piles are evaluated respectively as 0.98 and 1.46 by comparison of the bearing capacities for both of the static bearing capacity formulas and the Meyerhof method. It is also shown that uncertainty of the static bearing capacity formulas is relatively less than that of the Meyerhof method.

• Proceedings of the Korean Geotechical Society Conference
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• 2007.09a
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• pp.115-123
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• 2007

설계 하중이 큰 대형 구조물의 기초로 많이 사용되는 현장타설말뚝은 현장에서 지반을 굴착하여 조립된 철근망을 삽입한 후, 콘크리트를 타설하여 제작되므로 복잡한 시공 과정과 현장의 특수한 지하수 및 지반 조건으로 인하여 현장타설말뚝의 내부에는 결함이 포함될 수 있다. 발생 가능한 대표적인 결함으로 연약한 말뚝 선단, 말뚝체 콘크리트의 품질 저하, 말뚝과 지반의 접촉 불량, 주 철근의 부식 등이 있으며, 이들 결함을 감지하기 위한 건전도 시험법으로 공대공초음파 검층, 충격반향시험, 충격응답시험, 감마-감마 검층법 등이 있다. 결함은 말뚝의 수평지지력을 감소시키며, 일반적으로 발생하는 비대칭단면 결함에 의한 응력 집중현상과 수평 하중에 의한 휨모멘트는 연직지지거동에 영향을 준다. 따라서 결함을 감지하고 평가하는 것이 현장타설말뚝의 품질관리에 있어 매우 중요하다.

• Geotechnical Engineering
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• v.13 no.4
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• pp.13-24
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• 1997

A predicting method for ultimate vertical and horizontal bearing capacity by means of PAR(Pile Analysis Routines) was suggested. Based on the static pile load test data, case studies by means of PAR were performed. Ultimate pile capacity predicted by PAR was within 15% error range of that determined by stairs pile load tests. Also, the results of static pile load test, statnamic tests and PDA data performed on pipe piles were compared and, by using PAR, ultimate pile capacity was determined. Distributions of atrial pile load could be predicted and load transfer analysis could be done approximately by those distributions.

• Journal of the Korean Geotechnical Society
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• v.26 no.8
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• pp.27-37
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• 2010

Downdrag force develops when a pile is driven through a soil layer which will settle more than a pile. There is no obvious criterion for application of the current pile design method considering the negative skin friction. Therefore, in this study, numerical analyses were performed to investigate the behavior of a single pile subjected to negative skin friction and their results were used to determine the applicability of the current design method. Including three different sites in Song-do area and two different cases with friction pile and end bearing pile conditions, total six cases were considered. The load-settlement relationships and the neutral points were estimated for different end bearing conditions and the allowable bearing capacity of piles with negative skin friction was investigated through parametric studies. Based on the results showed that the negative skin friction made a major influence on the settlement of a pile and its stress. However the allowable bearing capacity may not be influenced by the negative skin friction. Compared with the allowable bearing capacity obtained from the ultimate bearing capacity with the safety factor of 3, the current design method with the safety factor of 3 underestimated the allowable bearing capacities regardless of the end bearing conditions. On the other hand, the current design method with the safety factor of 2 yielded reasonable results depending on the end bearing conditions.

• Journal of the Korean Geotechnical Society
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• v.32 no.4
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• pp.41-49
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• 2016

Pile foundations used as offshore support structures are dominantly subjected to cyclic lateral loads due to wind and waves. In this study, a series of cyclic lateral load tests were performed on a pre-installed aluminum flexible pile in sandy soil with three different relative densities (40%, 70% and 90%) in order to evaluate the effect of cyclic lateral loads on lateral load capacity of a pile. The cyclic lateral loads increased the lateral load capacity of a pile at 40% relative density, whereas they decreased it at 70% and 90% relative densities. This can be explained by the fact that the cyclic lateral loads slightly densified the surrounding soil in relatively loose sand (40%), while the surrounding soil was disturbed in relatively dense sand (70% and 90%). These effects were more obvious as the cyclic lateral load amplitude increased, being independent with the saturation. Also, from the test results, an empirical equation for the lateral load capacity of a cyclic laterally loaded pile in sandy soil was developed in terms of relative density of the soil and the cyclic lateral load amplitude.

• Geotechnical Engineering
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• v.9 no.1
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• pp.31-44
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• 1993

Model tests in calibration chamber with open -ended steel pipe pile have been performed in sand deposit to clarify effect of soil plug on bearing capacity, load transfer mechanisms in soil plug, and behavior of soil plug under dynamic and static conditions. Model piles were devised so that bearing capacity of open -ended pile could be measured separately into outside skin friction, inside skin friction due to soil plug -pile interaction and end bearing force on the section of steel pipe pile. It may be concluded, form the test results, that the plugging level of open -ended pile is more correctily defined by specific recovery ratio, y, rather than by plug length ratio, PLR, and the major part of inside skin friction is generated within the range of three times as long as the inner diameter of the pile from the pile tip. The ratio of inside skin friction to total bearing capacity is much larger than that of outside skin friction to total bearing capacity. Therefore, the bearing capacity of pile could not be well predicted, unless the inside skin friction is properly taken into account.

• Journal of the Korean Geotechnical Society
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• v.28 no.4
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• pp.5-21
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• 2012

In our country, in the case of traditional design of pile foundations, only a design depending on end bearing has been performed. However, through the load transfer measurement data that have been carried out for in-situ piles, it was known that skin frictional force was mobilized greatly. In this study, through the analysis of the load transfer test cases of driven steel pipe piles and large-diameter drilled shafts, load bearing aspects of pile foundation depending on pile construction methods and pile load test methods were established. The average sharing ratios of skin frictional force were independent of pile types, pile load test methods, relative pile lengths, pile diameters and soil types. Because the average sharing ratios were over 50%, the case pile foundations mostly behaved as a friction pile and the extremely partial case pile foundation behaved as a combined load bearing pile.