• Geomechanics and Engineering
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• 제10권5호
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• pp.577-598
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• 2016

This paper presents a numerical study of pile force distribution in a pile group foundation subjected to vertical load and large moment. The physical modeling of a pile foundation for a wind turbine is analyzed using 3D finite element software, PLAXIS 3D. The soil profile consists of several clay layers, which are modeled as Mohr-Coulomb material in an undrained condition. The piles in the pile group foundation are modeled as special elements called embedded pile elements. To model the problem of a pile group foundation, a small gap is created between the pile cap and underlying soil. The pile cap is modeled as a rigid plate element connected to each pile by a hinge. As a result, applied vertical load and large moment are transferred only to piles without any load sharing to underlying soil. Results of the study focus on pile load distribution for the square shape of a pile group foundation. Mathematical expression is proposed to describe pile force distribution for the cases of vertical load and large moment and purely vertical load.

• Earthquakes and Structures
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• 제19권4호
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• pp.273-286
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• 2020

The pile group foundation is widely used for gravity pier of high-speed railway bridges in China. If a moderate or strong earthquake occurs, the pile-surrounding soil will exhibit obvious nonlinearity and significant pile group effect. In this study, an improved pushover analysis model for the pile group foundation with consideration of pile group effect is presented and validated by the quasi-static test. The improved model uses simplified springs to simulate the soil lateral resistance, side friction and tip resistance. PM (axial load-bending moment) plastic hinge model is introduced to simulate the impact of the axial force changing of pile group on their elastic-plastic characteristics. The pile group effect is considered in stress-stain relations of the lateral soil resistance with a reduction factor. The influence factors on nonlinear characteristics and plastic hinge distribution of the pile group foundation are discussed, including the pier height, longitudinal reinforcement ratio and stirrup ratio of the pile, and soil mechanical parameters. Furthermore, the displacement ductility factor, resistance increase factor and yielding stiffness ratio are provided to evaluate the seismic performance of soil-pile system. A case study for the pile group foundation of a railway simply supported beam bridge with a 32 m-span is conducted by numerical analysis. It is shown that the ultimate lateral force of pile group is not determined by the yielding force of the single one in these piles. Therefore, the pile group effect is essential for the seismic performance evaluation of the railway bridge with pile group foundation.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 기초기술학술발표회
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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.

• Geomechanics and Engineering
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• 제16권2호
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• pp.187-194
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• 2018

Application the pile group foundation to reduce overall settlement of the foundation and also avoid a very fruitful settlement of foundations, inconsistent was carried out. In such a case, in event that the Foundation, not as a mere pile group, which as a system consisting of a broad foundation with pile Group, economic design criteria will be provided in spite of high safety. A new approach in the design of the Foundation can be introduced as the piles are just a tool to improve the parameters of soil hardness; that it can work with detachable piles from raft. Centralized arrangement of piles as the most optimal layout of piles in reducing inconsistent settlement, which is the lowest value of resulting layout in this differential settlement. Using the combination of piles connected and disconnected to form the raft, bending moment created in the raft is reduced. It also concentrated arrangements have greatest effect in reducing amount of moment applied to the raft.

• Earthquakes and Structures
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• 제3권3_4호
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• pp.495-506
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• 2012

An elasto-dynamic model for pile-soil-pile interaction together with a simple plate model is used in this study to assess the effect of flexible foundation slabs on the dynamic response of pile groups. To this end, different pile configurations with various slab thicknessesare considered in two soil media with low and high elastic moduli. The analyses include dynamic impedances and seismic responses of pile-group foundations. The presented results indicate that the stiffness and damping of pile foundations increase with thickness of the foundation slab; however, the results approach those for rigid slab as the slab thickness approaches twice the pile diameter for the cases considered in this study. The results also reveal that pile foundations with flexible slabs may amplify the earthquake motions by as much as 10 percent in the low to intermediate frequency ranges.

• Geomechanics and Engineering
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• 제23권6호
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• pp.513-521
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• 2020

In this paper, due to the need for cutting cement-soil group pile composite foundation under the 7-story masonry structure of Zhenghe District and the shield tunnel of Zhengzhou Metro Line 5, a field test was conducted to directly cut cement-soil single pile composite foundation with diameter Ф=500 mm. Research results showed that the load transfer mechanism of composite foundation was not changed before and after shield tunnel cut the pile, and pile body and the soil between piles was still responsible for overburden load. The construction disturbance of shield cutting pile is a complicated mechanical process. The load carried by the original pile body was affected by the disturbance effect of pile cutting construction. Also, the fraction of the load carried by the original pile body was transferred to the soil between the piles and therefore, the bearing capacity of composite foundation was not decreased. Only the fractions of the load carried by pile and the soil between piles were distributed. On-site monitoring results showed that the settlement of pressure-bearing plates produced during shield cutting stage accounted for about 7% of total settlement. After the completion of pile cutting, the settlements of bearing plates generated by shield machine during residual pile composite foundation stage and shield machine tail were far away from residual pile composite foundation stage which accounted for about 15% and 74% of total settlement, respectively. In order to reduce the impact of shield cutting pile construction on the settlement of upper composite foundation, it was recommended to take measures such as optimization of shield construction parameters, radial grouting reinforcement and "clay shock" grouting within the disturbance range of shield cutting pile construction. Before pile cutting, the pile-soil stress ratio n of composite foundation was 2.437. After the shield cut pile is completed, the soil around the lining structure is gradually consolidated and reshaped, and residual pile composite foundation reaches a new state of force balance. This was because the condensation of grouting layer could increase the resistance of remaining pile end and friction resistance of the side of the pile.

• Geomechanics and Engineering
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• 제38권2호
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• pp.139-155
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• 2024

The piled raft foundations are subjected to lateral loading under the action of wind and earthquake loads. Their bearing behavior and flexural responses under these loadings are of prime concern for researchers and practitioners. The insufficient experimental studies on piled rafts subjected to lateral loading lead to a limited understanding of this foundation system. Lateral load sharing between pile and raft in a laterally loaded piled raft is scarce in literature. In the present study, lateral load-displacement, load sharing, bending moment distribution, and raft inclinations of the piled raft foundations have been discussed through an instrumented scaled down model test in 1 g condition. The contribution of raft in a laterally loaded piled raft has been evaluated from the responses of pile group and piled raft foundations attributing a variety of influential system parameters such as pile spacing, slenderness ratio, group area ratio, and raft embedment. The study shows that the raft contributes 28-49% to the overall lateral capacity of the piled raft foundation. The results show that the front pile experiences 20-66% higher bending moments in comparison to the back pile under different conditions in the pile group and piled raft. The piles in the piled raft exhibit lower bending moments in the range of 45-50% as compared to piles in the pile group. The raft inclination in the piled raft is 30-70% less as compared to the pile group foundation. The lateral load-displacement and bending moment distribution in piles of the single pile, pile group, and piled raft has been presented to compare their bearing behavior and flexural responses subjected to lateral loading conditions. This study provides substantial technical aid for the understanding of piled rafts in onshore and offshore structures to withstand lateral loadings, such as those induced by wind and earthquake loads.

• Geomechanics and Engineering
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• 제39권3호
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• pp.227-240
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• 2024

This study investigates the control effect of isolation piles on ground settlement resulting from foundation pit excavation. Based on the three-stage analysis method, first, the Kerr three-parameter foundation model is introduced, and the deflection differential equation is derived to solve the horizontal displacement of the diaphragm wall. Then, based on the horizontal displacement of the diaphragm wall, the boundary element method is used to calculate the additional stress at the boundary of the foundation pit, and the horizontal additional displacement and additional stress of the soil free field at the position of the isolation pile are obtained using the Mindlin solution. Subsequently, soil free field additional stress is applied to the pile foundation, and the shielding effect of group piles is also considered. Based on the Kerr three-parameter foundation model, the deflection differential equation of the pile foundation under the influence of horizontally oriented additional stress is established to solve the horizontal displacement of the isolated piles. Finally, the boundary element method is used again to invert the additional stress caused by the horizontal displacement of the isolation pile, and the surface settlement after the isolation pile is calculated in combination with the Mindlin vertical displacement solution. The spatial finite element model is established and compared with the theoretical calculation results to prove the rationality of the theory. The influence of basic construction parameters is analyzed theoretically, and it is found that the surface settlement is reduced by 30.9% compared with no isolation pile. Of the selected parameters in this paper, the effects of the isolation pile's controlled diameter, spacing, and elastic modulus, the thickness and elastic modulus of the diaphragm wall on the surface settlement are 4.9 mm, 3.1 mm, 3.3 mm, 3 mm, 1.7 mm, respectively, which are 45.4%, 28.7%, 30.6%, 27.8%, 15.7% of the standard working conditions, respectively. This shows that optimization of the isolation pile parameters has the best effect on surface settlement, optimization of the diaphragm wall parameters has the poor effect.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회
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• pp.515-518
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• 2010

Horizontal forces may form a major part of the loading system for structures supported on pile groups. It is known that during a strong earthquake, the dynamic behavior of a group-pile foundation is related not only to the inertial force coming from the superstructures but also to the deformation of the surrounding ground. Therefore, it is necessary to understand the behaviors of the group-pile foundations and superstructures during major earthquakes. In this paper, numerical simulation of real-scale group-pile foundation subjected to horizontal cyclic loading is conducted by using a program named as DBLEAVES. In the analysis, nonlinear behaviors of ground and piles are described by cyclic mobility model and axial force dependent model (AFD model). The purpose of this paper is to prove availability of the analysis method by comparing numerical results and test results.

• 한국지반공학회논문집
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• 제28권2호
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• pp.57-70
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• 2012

연약지반에 시공되는 송전철탑의 경우 말뚝기초가 주로 사용되나, 부등침하로 인한 철탑구조물의 손상이 유발될 수 있으며, 이에 따라 미국과 일본에서는 4각의 기초를 연결보로 연결한 연결형 기초의 사용을 추천하고 있다. 본 연구에서는 송전철탑에 작용하는 하중조건과 연결보의 강성조건이 연결형 말뚝기초의 수평거동에 미치는 영향을 조사하기 위해서 1/8 규모의 축소모델을 이용한 연결형 말뚝기초의 수평재하시험을 수행하였다. 본 시험결과 연결형 기초는 말뚝기초에 비하여 지지력이 크고 부등변위등의 송전철탑의 안전성을 저해하는 요인에 저항하는 효율적인 기초 형식인 것으로 나타났으며, 특히 연결보의 상대강성에 따른 효과를 분석한 결과 연결보의 강성이 매트의 강성대비 25%에서 연결형 기초의 형식으로 사용의 효율성이 좋은 것으로 나타났다.