• Journal of the Korean Geotechnical Society
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• v.21 no.10
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• pp.73-83
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• 2005

Recently, foundation designs based on piled raft concept have been increasing, where the piles are required not to ensure the overall stability of the foundation but to act as settlement reducer. When a concrete track is constructed on soft ground, excessive settlements may occur, while it rarely has bearing capacity problems. In this case, the settlement of the concrete track may be effectively reduced by arranging a small number of small-diameter piles beneath the track. This paper presents the effect of pile installation on the reduction of concrete track's settlement. A 3D finite difference method was employed to model the piled concrete tracks. A parametric study was carried out to assess the effect of varying soil condition and pile arrangements. From the analysis results, it is verified that the effect of the pile installation is significant to effectively reduce the settlement of concrete track. Optimal number of pile rows and pile spacings was proposed for the economical design of a piled concrete track. The bearing mechanism of piles was also investigated by analyzing load sharing characteristics of pile according to soil conditions and pile arrangements.

• Journal of the Korean Geotechnical Society
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• v.35 no.1
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• pp.17-30
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• 2019

This study presents the application of the numerical and analytical technique to simulate the Load Distribution Ratio (LDR) and to define axial stiffness on reinforcing pile foundation ($K_{vr}$) in vertical extension remodeling structure. The main objective of this study was to investigate the LDR between existing piles and reinforcing piles. Therefore, to analyze the LDR, 3D FEM analysis was performed as variable for elastic modulus, pile end-bearing condition, raft contacts, and relative position of reinforcing pile in a group. Also, using the axial stiffness ($K_{ve}$) of existing piles, the axial stiffness of reinforcing pile was defined by 3D approximate computer-based method, YSPR (Yonsei Piled Raft). In addition $K_{vr}$ was defined by reducing the $K_{ve}$considering the degradation of the existing piles.

• Journal of the Korean Geotechnical Society
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• v.29 no.12
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• pp.57-67
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• 2013

Micropile technology has evolved continuously since its instruction by Fernando Lizzi in the 1950s. The effects of group micropile have been researched by many researchers. The effects of group micropile differ and change with pile length, pile spacing (S), pile angle (${\theta}$) and pile embedded conditions. In the present study, the effects of resistance increase and settlement reduction from micropiles were investigated through a series of axial load tests. For the study, axial load tests were performed using mat, group micropiles and micropiled-raft (MPR) in various pile spacing and pile angle conditions. As the result, the effects of resistance of micropiled-raft were 80% (3D) to 110% (7D) of the total resistance of mat and group micropile. The effects of settlement restraint of micropiled-raft were 20% (S=3D, ${\theta}=45^{\circ}$) to 70% (7D, ${\theta}=15^{\circ}$) of settlement of mat foundation.

• Journal of the Korean Geotechnical Society
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• v.22 no.4
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• pp.95-104
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• 2006

For the interests in the economical and safe design of foundation system, the concern on the piled raft or disconnected piled raft foundation system is increasing now. In this study, the behavior and the effects of the disconnected piled raft foundation not studied actively in this country were examined using the triaxial compression tests in place of laboratory model tests. The triaxial test samples were prepared with Jumunjin standard sand and the carbon rods, which simulate the ground soil and piles respectively. After the sample in which carbon rods were arranged was laid inside the triaxial chamber, the confining pressure was applied and then loading test was conducted. To analyze the reinforcing effects of the disconnected piled raft foundation, a few number of tests were carried out by changing the number, the diameter and the length of the model piles. As a result of this study, in the disconnected piled raft foundation system, even though the number of pile is few and the diameter of pile is small, the settlement of the foundation system decreased greatly.

• Journal of the Korean Geotechnical Society
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• v.24 no.11
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• pp.25-34
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• 2008

An application of concrete track is being actively processed for the construction of Korean high speed railway. The concrete track has an advantage in decreasing the maintenance cost, whereas it has much difficulty controlling the long term settlement after settlement occurred. Therefore, the management and control of settlement are very important for the successful construction of concrete track. The purpose of this paper is to verify the allowable settlement between concrete track and ballast track, and piled raft foundation installation effects as settlement reducers for concrete track. Therefore, a series of 3D finite element analyses that take into account the allowable settlement were performed for major parameters such as soil condition, pile installation and loading type. Based on the analysis, it is shown that concrete track causes much smaller settlement than ballast track, and the effect of installation is necessary to effectively reduce the settlement of concrete track.

• Journal of the Korean Geotechnical Society
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• v.25 no.11
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• pp.17-26
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• 2009

The concrete cap, which was established on the top of the micropile, usually considered as an important structural component in micropile supported foundation systems. However, relatively few studies have been made on the load sharing behavior of the capped micropile foundation systems. The primary objective of this study is to assess the load sharing behavior of the capped micropile foundation systems. Therefore, a full-scale test on an instrumented capped micropile is conducted for establishing the load-displacement responses. Nonlinear numerical method was used to quantify the load sharing behavior of the pile cap and micropile respectively. As a result, it was found that the pile cap shares about 50% load from final loading steps in the case of 2 by 1 micropile foundation systems. In the case of 2 by 2, the pile cap shares about 30% load from final loading steps. In addition, the load sharing behavior of the micropile cap becomes larger with an increase in spacing and the battered angle of micropile respectively.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.11a
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• pp.102-117
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• 2002

The general design practice for piled footings is based on the assumption that the piles are free-standing, and that all the external loads are carried by the piles, with any contribution of the footing being ignored. This approach is not reasonable, because the footing itself is actually in direct contact with the soil, and thus carries a significant fraction of the loads. In the case of not considering the bearing capacity of footing, the bearing capacity of group piles can be evaluated conservatively in the designing the group piles. There are a number of reasons why the idea of piled raft design with considering the capacity of footing has not become widely used. One of the reasons is the lack of reliable calculation methods for estimating the behavior of piled raft. In this study the bearing capacity, settlement, load distribution, etc. of piled raft footing are studied.

• The Journal of Engineering Geology
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• v.29 no.4
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• pp.451-460
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• 2019

In this study, a complex behavior connector is proposed to overcome the problems that may occur when small pile pipe and micro pile is used as a friction pile concept in the lower foundation of an oil sand plant where a piloti foundation is used. The individual settlement and heaving of piles were connected in one group to allow the composite behavior. This study performed to analyze the load carrying capacity to identify a complex behavior. In addition, the shape of the composite behavior connector was examined to apply the advantages of pile-group and piled raft foundations to oil sand plants. A scale model was constructed to measure the behavior of the load. The stability and weakness of the device were selected to determine the shape of the connector using the scale model testing.

• Journal of the Korean Geotechnical Society
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• v.40 no.2
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• pp.41-53
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• 2024

Micropiles are small, cast-in-place piles with a diameter of 300 mm or less, primarily used to reinforce existing structures and support new constructions. As the application of these piles has expanded, extensive research has been conducted on their bearing characteristics, particularly in micropiled rafts. These studies have consistently demonstrated the positive impact of micropiles on foundation reinforcement. However, previous research often overlooked the potential variations in behavior between micropiled and conventional piled rafts based on different pile conditions. Furthermore, the influence of the cohesive characteristics of the soil layer beneath the foundation on the reinforcing effect of the micropiles has not been adequately addressed. This study, therefore, undertook 3D numerical analysis to assess the reinforcing effect of micropiles, considering both pile conditions and the cohesive characteristics of the soil layer beneath the foundation. The findings revealed that micropiles are significantly more effective in non-cohesive soil layers compared to cohesive ones, with the potential to increase the bearing capacity of the raft by up to 3.7 times.

• Proceedings of the Korean Geotechical Society Conference
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• 2003.03a
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• pp.439-446
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• 2003

In this paper the model tests have been conducted and the results are compared with those by the theoretical methods to study the behaviors of the piled raft. The size of model box is 2.2m${\times}$2m${\times}$2m. The raft is made of rigid steel plate and piles made of steel pipes. Generally the bearing capacity of group piles is designed with only the pile capacities, and the bearing capacity of raft is ignored. But the uncertainty of pile-raft-soil interaction leads to conservative design ignoring the bearing effects of raft. In the case of considering the bearing capacity of raft, the simple sum of bearing capacity of raft and that of each pile cannot be the bearing capacity of piled raft. Because the pile-raft-soil interaction affects the behavior of piled raft. Thus the effects of pile-raft-soil interaction are very important in the optimal design. In this paper, the behaviors of piled raft are studied through model tests of 2${\times}$2, 2${\times}$3, and 3${\times}$3 pile groups. The spacing between piles is changed in the model tests. And the behaviors of free standing and piled raft are also studied.