• Computers and Concrete
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• v.25 no.6
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• pp.525-535
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• 2020

The use of pile foundations has become more popular in recent years, as the combined action of the pile cap and the piles can increase the bearing capacity, reduce settlement, and the piles can be arranged so as to reduce differential deflection in the pile cap. Piles are relatively long, slender members that transmit foundation loads through soil strata of low bearing capacity to deeper soil or rock strata having a high bearing capacity. In this study analysis of pile cap with considering different parameters like depth of the pile cap, width and breadth of the pile cap, type of piles and different types of soil which affect the behaviour of pile cap foundation is carried out by using Finite Element Software ANSYS. For understanding the settlement behaviour of pile cap foundation, parametric studies have been carried out in four types of clay by varying pile cap dimensions with two types of piles namely normal and under-reamed piles for different group of piles. Furthermore, the analysis results of settlement and stress values for the pile cap with normal and under-reamed piles are compared. From the study it can be concluded that settlement values of pile cap with under-reamed pile are less than the settlements of pile cap with normal pile. It means that the ultimate load bearing capacity of pile cap with under-reamed piles are greater than the pile cap with normal piles.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.245-252
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• 2000

Model tests on free standing pile groups and piled footings with varying a pile spacing in two layered soils are carried out. The influence of pile cap on the behaviors of end bearing pile groups is analyzed by comparing the bearing behavior in piled footings with those in a single pile, a shallow footing(cap alone) and free standing pile groups. From the test results, it is found that the bearing characteristics of cap-soil-pile system are related with load levels and pile spacings. Before yield, the bearing resistance by cap is not fully mobilized, however, as the applied load increases, the bearing resistance of cap approaches to that of cap alone and settlement hardening occurs after yield due to the compaction caused by the contact pressure between cap and soil. By the cap-soil-pile interaction, shaft friction and point resistance of piles considerably increase with dependency of pile spacings. In two layered soil, the increasing effect of dilatancy in dense sandy soil adjacent to pile tips, increases the point resistance of pile.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.03a
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• pp.259-266
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• 1999

In case that pile cap is in direct contact with underlying soil, the bearing mechanism for pile groups, including direct bearing effect of cap and its induced influence on pile-soil-cap interaction, should be properly considered. In this paper, the effects of pile caps on behaviors of pile groups in sandy soils were investigated by model tests, which consist of tests on 3 by 3 pile groups with/without contact on subsoil, single pile with/without contact and cap as a shallow foundation. Also, the influences of pile spacing in group piles on contact effects were investigated. The test results showed that the load carrying capacity of pile cap was large enough not to be ignored. However, the interaction effects due to contact between cap and subsoils were not revealed obviously in working load range. And in the design of pile groups, the bearing effect of pile cap when contacted with subsoils, can be reflected by simply summing up load settlement behaviors of each cap and group piles without contact.

• Journal of the Korean GEO-environmental Society
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• v.19 no.7
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• pp.5-11
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• 2018

Instead of a single pile, group piles are usually used for the pile foundation. If the earthquake occurs in the ground where group piles are installed, dynamic behavior of group piles are affected not only by interaction of piles and the ground movement but also by the pile cap. However, in Korea, the pile cap influence is not taken account into the design of group piles. Research on dynamic behavior of group piles has been performed only to verify interaction of piles and the ground and has not considered the pile cap as a factor. In this research, 1g shaking table model tests were performed to verify the thickness of the pile cap affects dynamic behavior of group piles that were installed in the ground where the earthquake would occur. The test results show that, as thickness of the pile cap increased, acceleration and horizontal displacement of the pile cap decreasd while vertical displacement of the pile cap increased. The results also showed that, among the group files tested, acceleration, horizontal displacement, and vertical displacement of the bearing pile are smaller than those of the friction pile.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.363-370
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• 2001

A computationally efficient algorithm to analyze a group pile behavior is proposed by consideration of both soil-pile and pile-cap interactions. Using toad transfer method the nonlinear characteristics of the soil-pile interaction for a single pile is modeled by piecewise linear soil springs (p-y, t-z, and q-z curves). Beam-column method, one of the most practical approaches, is used for numerical modeling of the soil-pile system. In addition to the group effect resulting from the soil-pile-soil interaction, for a more realistic analysis it is essential to consider the effect of pile-cap interaction including geometric configuration of the piles in a group and conectivity conditions between piles and the cap. This paper mainly focuses on the pile-cap interaction and the development of a rational numerical procedure of its incorporation with the beam-column method.

• Journal of the Korean Geotechnical Society
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• v.23 no.9
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• pp.39-49
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• 2007

The load deformation behavior of the cap-pile-soil system is investigated, based on numerical analysis. Special attention is given to consideration of pile cap flexibility. Rigid pile cap analysis and flexible cap analysis were conducted for comparison. A numerical method that takes into account the coupling between the rigidities of the piles, the cap, and the column has been introduced to analyze the response of pile group supported columns. The prediction of the lateral loads and bending moments in the pile cap is much more conservative for a flexible cap than for a rigid cap.

• Geomechanics and Engineering
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• v.33 no.5
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• pp.463-475
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• 2023

Tunnel construction activity, conducted mainly in mountains and within urban centres, causes soil settlement, thus requiring the relevant management of slopes and structures as well as evaluations of risk and stability. Accordingly, in this study we performed a three-dimensional finite element analysis to examine the behaviour of piles and pile cap stability when a tunnel passes near the bottom of the foundation of a pile group connected by a pile cap. We examined the results via numerical analysis considering different conditions for reinforcement of the ground between the tunnel and the pile foundation. The numerical analysis assessed the angular distortion of the pile cap, pile settlement, axial force, shear stress, relative displacement, and volume loss due to tunnel excavation, and pile cap stability was evaluated based on Son and Cording's evaluation criterion for damage to adjacent structures. The pile located closest to the tunnel under the condition of no ground reinforcement exhibited pile head settlement approximately 70% greater than that of the pile located farthest from the tunnel under the condition of greatest ground reinforcement. Additionally, pile head settlement was greatest when the largest volume loss occurred, being approximately 18% greater than pile head settlement under the condition having the smallest volume loss. This paper closely examines the main factors influencing the behaviour of a pile group connected by a pile cap for three ground reinforcement conditions and presents an evaluation of pile cap stability.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.06a
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• pp.77-89
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• 2002

To analyze a bearing capacity for pile groups, a number of model tests have been done and theoretical methods studied. In the case of design of group pile bearing capacity is calculated with only pile capacity. But uncertainty of bearing capacity and behavior of foundation cap(raft) leads to conservative design ignoring bearing effects of foundation cap. In the case of considering bearing capacity of foundation cap, the simple sum of bearing capacity of foundation cap and pile groups cannot be the bearing capacity of total foundation system. Since cap-pile-soil interaction affects the behavior of pile groups. Thus, understanding cap-pile-soil interaction is very important in optimal design. In this paper, the piled raft behavior is studied through model tests of 2$\times$2, 2$\times$3, 3$\times$3 pile group. Changes of behavior of pile group foundation by touching effects of foundation cap with soil are studied. Also changes of spacing between piles. Foundation cap is made of rigid steel plate and piles are made steel pipes. From this model tests, the changes of behavior changes of pile groups by touching effects of foundation cap with soil are studied.

• Structural Engineering and Mechanics
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• v.41 no.3
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• pp.395-406
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• 2012

Basic problem of pile foundation is three dimensional in nature. Three dimensional finite element formulation is employed for the analysis of pile groups. Pile, pile-cap and soil are modeled using 20 node element, whereas interface between pile or pile cap and soil is modeled using 16 node surface element. A parametric study is carried out to consider the effect of pile spacing, number of piles, arrangement of pile and soil modulus on the response of pile group. Results indicate that the response of pile group is dependent on these parameters.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.343-358
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• 2008

Piles of a bridge pier are connected with a column through a pile cap(footing). Behavior of the pile foundation can be different according to the connection method between piles and the pile cap. This difference causes a change of the design method. Connection methods between pile heads and the pile cap are divided into two groups ; rigid connections and hinge connections. KHBDC(Korea Highway Bridge Design Code) has specified to use rigid connection method for the highway bridge. In the rigid connection method, maximum bending moment of a pile occurs at the pile head and this helps the pile to prevent the excessive displacement. Rigid methods are also good to improve the seismic performance. However some specifications prescribe that conservative results through investigations for both the fixed-head condition and the free-head condition should be reflected in the design. This statement may induce an over-estimated design for the bridge which have very good quality structures with casing covered drilled shafts and the PC-house contained pile cap. Because the assumption of free-head conditions (hinge connections) are unreal for the elevated pile cap system with multiple piles of the long span sea-crossing bridges. On the other hand, elastic displacement method to evaluate the pile reactions under the pile cap is not suitable for this type of bridges due to impractical assumptions. So, full modeling techniques which analyze the superstructure and the substructure simultaneously should be performed. Loads and stress state of the very large diameter drilled shaft and the pile cap for Incheon Bridge which will the longest bridge in Korea were investigated through the full modeling for rigid connection conditions.