• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.4
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• pp.259-268
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• 1993

The downdrag on a single pile and on pile groups was examined by using a numerical analysis and an analytical study. The overall objective of the present study was given to the magnitude and distribution of the downdrag forces on piles within a group. The case of the single pile was analyzed by developing a closed form solution. Subsequently the response of groups was investigated by using a detailed numerical approach. Based on the results, it is found that the downdrag load of piles in a group is much smaller than that of a single pile. Also, a simple method is proposed to design groups of 9 to 25 piles with spacing-to-diameter ratios varying from 2.5 to 5.0 for downdrag loads.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.2
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• pp.343-354
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• 1994

The group effect which causes different downdrag distribution in individual piles within the group was investigated by using a numerical analysis and an analytical study. The interaction factors due to group spacing and total number of piles in a group were estimated by using a three dimensional non-linear finite element approach. Based on the results obtained, it is shown that the interaction factors of pile groups varies remarkably according to the group spacing, a major influencing parameter for the group effect. Also the downdrag prediction by the proposed method was compared with the other analytical methods through an example of calculations.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.2
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• pp.115-123
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• 1989

A computer program evaluating the pile downdrag is developed using the conventional elastic solid method. Modification of the conventional method has been performed by introducing the concept of critical relative displacement. A simple transfer function method which employes the critical relative displacement as a pile-soil slip criterion and calculates downdrag by Mohr-Coulomb equation, has also been developed. The results of three methods are all found to be in good agreement with field observations. When they are applied to a centrifuge modeling problem of pile downdrag to predict its result, however, diverse answers are obtained. Overall, the simple transfer function method developed in this study seems to be the most effective in the evaluation of pile downdrag, considering the quality of its result and its efficiency in computation.

• Geotechnical Engineering
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• v.3 no.1
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• pp.39-52
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• 1987

Model pile tests are performed, first, to estimate donwndrag exerted on pile surfaces due to the settlement of surrounding soils, and, second, to evaluate the efficiency of the downdrag reduction methods such as the bitumen coating method and the method of the attachment of an enlarged base. Test results show that the downdrag forces may be expressed as 0.25(;effective overburden). Bitumen coating reduces the downdrag by more than 50 percent, and the enlarged base attachment method is also effective, whose effectiveness increases as the sixte of the base increases as expected. When the bitumen coating and enlarged base are both applied, the downdrag force is reduced as much as 90 percent. Finally, it is found that the quantity of the relative displacement between the pile and the surrounding soil downdrag is extremely small.

• Journal of the Korean Geotechnical Society
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• v.21 no.5
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• pp.123-131
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• 2005

Recently, construction activities in reclaimed onshore areas increase in our country In this case, the stability evaluation of the piles for negative skin friction is an important factor for the design of pile foundation in soft grounds. Nevertheless, the design of piles for negative skin friction (or downdrag forces) is probably poorly understood by many geotechnical engineers. It is mainly because only the bearing capacity aspect is taken into account for the downdrag evaluation of piles in most of design specifications. However, the problems fur negative skin friction of piles are mostly related with settlement rather than bearing capacity Meanwhile, LRFD (Load Resistance Factor Design) approach considers both ultimate limit state in terms of bearing capacity and serviceability limit state in terms of settlements. This paper proposes LRFD approach for the downdrag evaluation of piles and compares this approach to traditional design approach. And also a case history is analyzed. Through the analysis some suggestions to solve the problems for the design of piles for negative skin friction are suggested.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.17-24
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• 2005

Recently construction activities increase in reclaimed onshore areas. It is therefore considered an important factor for the design of pile foundation with problems in terms of settlements due to soft grounds. Nevertheless the design of piles for negative skin friction(or downdrag forces) is probably poorly understood by many engineers. It is mainly because the most of design specification give a way to design pile foundation in bearing capacity aspect although the negative skin friction is related to settlement(downdrag). Under LRFD(load resistance factor design) approach it is to separately consider ultimate limit state and serviceability limit state. This paper discusses LRFD approach to the design of piles for negative skin friction and compares this approach to traditional design approach. And also a case history is analyzed in that point of view.

• Proceedings of the Korean Geotechical Society Conference
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• 1993.04a
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• pp.1-18
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• 1993

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.407-414
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• 2000

This paper presents measured deformation of geomembrane installed on slopes of a landfill. The layout of geosynthetics installed on landfill slopes as required by regulations is composed of, in typical, geocomposite, geomembrane, geosynthetic clay liner in turn from the slope. An effort was made to better understand the sources of external forces acting on geosynthetics and their interactions. The results of a field observation indicated that tensile stresses induced on geomebrane were far less in magnitude than predicted by the design method employing mass equilibrium of waste. This was mainly because external forces acting on slopes were not transferred from geocomposite to underlying geomembrane. A simple, but rather rational method for assessing the stability of geosynthetics against tensile stresses was proposed. This method is based on a hypothesis that external forces acting on geosynthetics are the results of downdrag of waste during waste compaction.

• Structural Engineering and Mechanics
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• v.3 no.5
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• pp.429-443
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• 1995

The deformational response of plastic board drains installed to accelerate consolidation of soft soils, is examined as a problem of downdrag. The drain is modelled as a beam-column in which the axial load increases nonlinearly with depth. The soil response is represented by the Winkler medium whose coefficient of subgrade modulus increases linearly with depth. The governing equations for the drain-soil system are derived and solved as an eigenvalue problem. The critical buckling loads and the shape of the drain are obtained as functions of the normalized subgrade modulus of the soil at the top, the parameters signifying the variation of axial load along the length of the drain and the increase of subgrade modulus with depth. The derived deformed shapes of the drain are consistent with the observed ones.

• Proceedings of the Korean Geotechical Society Conference
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• 1997.10a
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• pp.373-382
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• 1997