Behavior Of Piled Raft Foundation Research Articles

Static behavior of piled raft foundation in clay

Abstract Wall piles supported with anchors are considered one of the most prevalent types of engineering support. This research includes studying the behavior of wall piles through a numerical parametric study using the FE-method program (PLAXIS 2D). The study includes the most influencing factors such as the angle of the inclination, the vertical spacing between the rows of anchors, and the distance of the first row of anchors from the ground surface. The effects of these factors on the stability of the wall were studied. Optimal positioning of the anchors is crucial, as it maximizes their effectiveness and contributes significantly to reducing the overall construction costs. The use of a guys queue for the economic aspect saves the cost of executing two guys queue because the effect of having two rows does not significantly change the transfer values. The optimum angle of inclination of the tensioner row is 15° in favor of safety, and as it gives good stability of the wall to the wedge wall, with an increase in this angle, the horizontal movement decreases. The first optimum dimension for a row of guys from the horizontal surface of the earth is O = 25%H. Decrease the values of horizontal movement of the wall by increasing the angle of friction.

Settlement and load sharing behavior of piled raft foundation: a review

Settlement and load sharing behavior of piled raft foundation: a review

Effect of Pile Configuration on the Behavior of Piled-Raft Foundations in Sandy Soil

Abstract In this research, an experimental investigation to examine the behavior of piled-raft foundations in loose sand is introduced. A small-scale model was tested in a sandy soil container. Three sensors were fabricated on the pile heads to record the axial load induced by any pile in the group, and the foundation’s settlement was also measured. In addition to experiments for an unpiled raft, model groups for 1 pile, 1 × 2, 1 × 3, 2 × 2, 2 × 3, 3 × 3, 3 × 3 triangle heaps, 4 diamond piles, 5 piles, and 9 circle piles were tested in the lab. The loading test was carried out until a relative pile displacement of 10 % of the length of the raft was passed. It was found that the piled-raft models with piles placed in uniform configurations (2 × 2 and 3 × 3) showed an increase in bearing capacity higher than that of piled rafts with the circle and diamond configurations, but not higher than that of triangular configuration. Also, it was found that when the value of loading was 1,000 N and the pile spacing increased from 2.5d to 3d, the settlement increased from 11 to 13 mm, 9.5 to 11 mm, 8.5 to 10 mm, and 7 to 9 mm for models PR2, PR3, PR4, and PR5 (referring to 2-, 3-, 4-, and 5-piled-raft models), respectively. In practically the whole settlement range tested, the results demonstrated that the contribution of the edge and center piles was considerably higher than that of the single piles underneath the raft. The axial loads carried by the edge and the center piles for the PR9, PR5, and PR3 piled-raft types, respectively, were roughly 40 % and 70 %, 52 % and 70 %, and 20 % and 60 % higher than those for the PR1 pile capacity.

Static analysis of prestressed micropile-raft foundation with varying lengths resting on sandy soil

The micropile-raft system is used in the foundation system of buildings due to the combination of the advantages of raft foundations and micropiles. In this paper, the numerical model was calibrated and validated with a field test, and then several parametric studies were performed. The overarching aim of the study is to determine the efficiency of different arrangements of micropiles and the effects of these parameters on the behavior of piled raft foundations in sandy soil. Parameters including diameter, length, and distance of micropiles from each other were considered in the analyses. Prestressed rebars have been used to increase the load-bearing capacity and prevent premature buckling under severe compressive load. Therefore, to compensate for the weak bearing capacity of the raft foundation, a micropile system equipped with prestressed rebars was considered to increase the bearing capacity of the foundation. The results revealed that using a set of micropiles with a diameter of 30 cm and a length of 10 m had the maximum efficiency among other models. Furthermore, an innovative arrangement of micropiles was proposed in which a set of micropiles with a length of 30 m was placed at the middle region of the foundation, and in the peripheral area of the foundation, several short micropiles were used.

Behavior of Piled Raft Foundation in Soft Clay Layer with Geo-Foam Application

Piled raft system proves to be more effective on such problematic soft soil conditions. It takes the high vertical load and used to bring the settlement, differential settlement and tilting of structure within the permissible limit. Piled raft system proves to be cost effective than the conventional pile foundation system. Piled raft foundation accounts for complex soil-structure interaction, which needs interaction between structural engineer and geotechnical engineer. Geo-foam application is introduced below the footing to enhance floating resistance. The performance behavior of piled raft foundation in clayey soil and layered soil is carried out using laboratory experimental and then verified by 2D PLAXIS. There is a significant relationship between the decreases in settlement of the piled raft due to hydrostatic uplift.

The behaviour of piled raft foundation in loose sandy soil

The conducts of pile raft basis depend on piles, raft, as well as soil. When designing a pile group, it is expected that only the piles carry out the applied loading. No contribution is given to soils underneath the raft because of the complicated interacting amid the piles and their cap with soils. When the soil under the raft foundation shares carrying the applied loads, this interaction will increment the piled raft system’s bearing capability as well as decrease the settlements. To comprehend the piled raft system’s complicated conduct, testing for twenty-seven experimental models was done within loose sands with a load applied to the piled raft foundation via a compressing jack then the measurement was done using a loading cell. Wide parametrical examinations had been executed with the variables number of piles, pile length, raft dimension ratio. The soil under the raft contributed a certain percentage in carrying the applied weights in the piled raft foundation. Similarly, there is an increase in the loading taken via piles to the overall load executed on pile raft with the growth of the number of piles in the series, and there is a decrease in the share of the soil under the raft for the applied loads when there is increasing within the piles’ amounts. The increment within the piles’ lengths causes an increase in the soil’s share underneath the raft, and the maximum settlement of the piled raft system does not exceed 5% of the raft width in all cases.

Investigating the behavior of piled raft foundation in core wall foundation of high-rise buildings

Core structure is an indispensable part of high buildings. Normally, the foundation of the core structure has a raft of larger size than the other foundations in the same project; therefore, the foundation of the core structure can be viewed as a small piled raft foundation. Currently, when calculating the piled foundation of the core, it is mostly assumed that the piles system will bear all the project loads. But this calculation method is not suitable for the actual constructions as well as does not make full use of the bearing capacity of the structure and the ground, leading to using more materials and causing more waste. Core structure aims to increase both stiffness and horizontal load capacity in high-rise buildings, so the moment inside the core transmitted to the foundation is very large. One of the shortcomings of the Plaxis 3D Foundation software is its inability to declare the moment affecting on the foundation due to the loads in this program just includes distributed loads, line loads and point loads in the geometry model. Consequently, when using Plaxis 3D Foundation software to calculate the core wall foundation of high-rise buildings, this moment is converted into an equivalent pair of moments. The research shows that when the core foundation of a high-rise building is placed on soft soil, the pile carries 96%, most of the load transmitted to the foundation. However, when the foundation is placed on hard soil, the soil surrounding the raft will bear about 10% of the load transmitted to the foundation. If this matter is skipped, there will be a large error in calculation and design.

Three-dimensional numerical analysis on seismic behavior of soil-piled raft-structure system

Increasing demand for high-rise buildings and other important structures in urban areas and unfavorable land has resulted to opt for piled raft foundation by the designers. The present study is an attempt to investigate the seismic behavior of piled raft foundation supporting structural system embedded in very soft clay encompassing variations of different influential parameters. The piled raft system is modeled using three-dimensional (3D) finite element analysis. At first, the 3D numerical model is validated with past numerical studies. This is followed by a detailed parametric study on the effect of different influential parameters, such as flexibility of raft, pile spacing to diameter ratios, and asymmetry in pile length on dynamic characteristics and seismic response of the piled raft foundation system considering dynamic soil-structure interaction (DSSI). It is observed that the fundamental period of the structure gets significantly lengthened with increasing raft flexibility whereas pile head shear considerably reduced. Further, non-identical pile lengths attributing asymmetric group configuration results in a significant change in the fundamental period of the structure and pile head shear.

Behaviour of piled raft foundation in sand subjected to combined V-M-H loading

A combined piled raft foundation (CPRF) is generally used for massive and tall structures. The conventional design of piled raft does not include the capacity of piled raft under combined lateral and vertical load. However, vertical (V), horizontal (H) and moment (M) loading may act on the foundation simultaneously. The present study examines the behaviour of piled raft foundation in sandy soil under V-M-H interaction using three-dimensional finite element analysis. The horizontal and moment capacity of piled-raft is assessed due to various influential parameters, such as relative stiffness of pile and soil, raft-soil relative stiffness, spacing to diameter ratio of the pile, length to width ratio of the foundation and pile head connection with the raft. It is observed that piled-raft lateral capacity increases due to combined loading than that of independent capacity. Both failure and design envelopes are also developed considering V-M-H interaction. Finally, the design implication of the outcome of the present study is presented using a case study. It is revealed that the design of piled raft with lateral capacity obtained from the combined action of the V-M-H load may reduce the number of piles as compared to conventional design performed using individual capacity.

<b>Influence of relative stiffness on the behavior of piled raft foundations

The behavior of piled foundations is influenced by several factors, especially those related to the geometry of the foundations, the number of piles, the height of the element that tops the piles and the type of soil in which the foundations are inserted. Given the various situations and variations of parameters to be analyzed, it is common to use numerical modeling for the analysis of geotechnical engineering problems. The piled rafts in this article are numerically analyzed by means of the three-dimensional finite element method using CESAR-LCPC ® v.5 software. Thus, it was possible to conduct various analyses of piled rafts by varying the amount of piles and the thickness of the raft supported on the soil and piles. The results demonstrate that piled raft foundations tend to make displacements uniform, thus minimizing problems with differential settlement in structures. The thickness of the plate of the piled raft influences the load distribution in the piles under the raft when the piles are supported on the ground. The relative stiffness (K rs ), which is the ‘stiffness’ of the piled raft combined with the soil, increases with increases in the amount of piles and the thickness of the piled raft.

A laboratory study of the effect of piles asymmetric arrangement on the behavior of piled raft foundation in sand

Nowadays, the employment of piled rafts foundations as a solution for decrease of settlement is common. The number of piles and their configuration are determined that settlement of the foundation decreases to an allowable value. In these situations, the configuration of piles is determined in optional manner and strategically. This paper concentrates on laboratory study of effect of asymmetric arrangement of piles beneath the raft in sand. The piles and raft models were made of cast-cast-in-place concrete. The physical models consisted of single pile, single pile in pile group, unpiled raft and piled raft foundation with symmetrical and asymmetrical piles arrangement. The results showed that in the asymmetrical models, increase of bearing capacity due to increase of the number of piles was inefficient and tilt of the foundation increased, significantly. In some of these asymmetrical models, available analytical method overestimated the load capacity of the piled rafts.

An investigation about seismic behavior of piled raft foundation for oil storage tanks using centrifuge modelling

Some level of settlement is allowed in the design of oil tank if the uneven settlement can be controlled in an allowable value. Considering a critical condition of piled raft foundation (PRF), that is, secure contact of raft base to the ground surface, and the expected function of piles to impose additional resistance against the local settlement, PRF is considered as one of the rational foundation systems for the oil tanks. However, PRF has a complex interaction with soil under horizontal seismic loading, especially if the tank rests on a liquefiable soil, which may cause an extreme change of the soil stiffness underneath the tank. In this study, a series of centrifuge model tests was performed to investigate the mechanical behavior of oil tank supported by piled raft foundation on liquefiable saturated sand and non-liquefiable dry sand. In the tests, two types of foundation were modelled; a slab foundation, and a piled raft foundation. Using the observed results, such as accelerations of the tank and ground, dynamic and permanent displacement of the foundation, and excess pore water pressures of the ground, advantages and limitations of piled raft foundation for application to oil tanks on sandy soil are discussed.

3-D NUMERICAL ANALYSIS OF CONSOLIDATION EFFECT ON PILED RAFT FOUNDATION IN BANGKOK SUBSOIL CONDITION

This study focused on the investigation of influencing factors on behaviour of piled raftfoundation in Bangkok subsoil. To evaluate the possibility of implementing this system in Bangkok subsoilcondition, this research performed the consolidation analysis of piled raft foundation systems for low-rise (8-storey) and high-rise (25-storey) buildings with basement levels in clay soil, using coupled three-dimensional(3D) mechanical and hydraulic numerical model. The soils are modelled with Hardening Soil model andMohr-Coulomb model. Evaluations of piled raft foundation, i.e., the load sharing ratio of piles, settlementbehaviours in the foundation system are performed. The parametric study on the effect of raft depth, and loadcarried by piles of piled raft was done. The consolidation had a strong influence on the load carried by pilesof the piled raft foundation in Bangkok. The load shared by piles can increase by up to 12% and 6% for lowrise and high-rise buildings, respectively due to the consolidation effect. Therefore, the design of the piledraft foundation system in Bangkok subsoil essentially consider the consolidation effect.

ANALYTICAL STUDY ON PILED-RAFT FOUNDATION CONSIDERING NONLINEAR BEHAVIOR OF GIBSON SOIL

Randolph (1994) was proposed simplified estimated equations to carried out the proportion of load between the components of piled-raft foundation. These equations are based on elastic theory. Therefore, Authors focus on the point of applicability for nonlinear behavior of soil. This paper is a part of study on behavior of piled-raft foundation under considering the nonlinear behavior of ground. Authors already discussed the effect of nonlinear behavior of soil on the equations by Randolph. In addition, as the extension of research, authors also discussed the applicability of these equations for irregular raft shape. However, foundations were rarely set in an ideal homogeneous single soil layer in our previous studies. Therefore, the applicability of these equations are discussed in case of inhomogeneous soil (Gibson soil) in this paper.

Effect of interactions between piled raft components and soil on behavior of piled raft foundation

The use of piled raft foundations has been considered as an economical alternative to conventional deep foundations because a portion of the applied load is thought to be transferred to the raft. In analyzing the behavior of a piled raft as a settlement reducer, an accurate estimate of settlement of the system should be made, based on the adequate understanding of nonlinear behavior of piles in layered soils as well as the interaction between the raft, soils, and piles. This study developed a computer program incorporating an approximate hybrid analysis method for the practical design of piled raft foundations. In the presented method of analysis, the interactions between pile-soil, raft-soil, pile-soil-pile and raft-soil-pile are considered, and the effect of nonlinear behavior of piles and the interactions between piled raft components and soil are investigated by comparing with 3-dimensional FEM program analysis results.

Settlement behavior of piled raft foundation supporting a 300 m tall building in Japan constructed by top-down method

Settlement behavior of piled raft foundation supporting a 300 m tall building in Japan constructed by top-down method

3D Finite Element Analysis on Behaviour of Piled Raft Foundations

This paper highlights settlement behaviour of piled raft foundation by 3D finite element analysis through Plaxis 3D Foundation program. The effects of pile number, pile length, pile layout and pile spacing on the behaviour of piled raft foundation were studied. The numerical results show that: Piled raft foundation has much more efficency to reduce settlement than that of traditional raft foundation. The value of vertical defomation decreases as the result of the increase of pile number, pile length, pile spacing and vice versa. Pile layout has significant effect on both value and location of maximum settlement of piled raft foundation.

Time dependent behavior of piled raft foundation in clayey soil

Settlement of the piled raft can be estimated even after years of completing the construction of any structure over the foundation. This study is devoted to carry out numerical analysis by the finite element method of the consolidation settlement of piled rafts over clayey soils and detecting the dissipation of excess pore water pressure and its effect on bearing capacity of piled raft foundations. The ABAQUS computer program is used as a finite element tool and the soil is represented by the modified Drucker-Prager/cap model. Five different configurations of pile groups are simulated in the finite element analysis. It was found that the settlement beneath the piled raft foundation resulted from the dissipation of excess pore water pressure considerably affects the final settlement of the foundation, and enough attention should be paid to settlement variation with time. The settlement behavior of unpiled raft shows bowl shaped settlement profile with maximum at the center. The degree of curvature of the raft under vertical load increases with the decrease of the raft thickness. For the same vertical load, the differential settlement of raft of (10x10 m) size decreases by more than 90% when the raft thickness increased from 0.75 m to 1.5 m. The average load carried by piles depends on the number of piles in the group. The groups of (2x1, 3x1, 2x2, 3x2, and 3x3) piles were found to carry about 24%, 32%, 42%, 58%, and 79% of the total vertical load. The distribution of load between piles becomes more uniform with the increase of raft thickness.

A Settlement Compensation Method for Design of Settlement Controlled Piled Raft Foundations under Vertical Loadings

In order to analyze the behavior of piled raft foundations under vertical loadings, a simplified method called settlement compensation method (SCM) is proposed based on the basic principles in the code for design of building foundation of China. The effect of several influence factors of the SCM was investigated through an exemplar case. The applicability and accuracy of SCM was checked theoretically with a finite element analysis, and verified practically through a case study in which the results of settlement analysis of other methods were included for comparison.

말뚝지지 전면기초의 3차원 근사해석기법 개발

철지반의 비선형성을 고려한 말뚝지지 전면기초의 3차원 해석기법(YSPR)을 개발하였다. 전면기초는 6개의 자유도를 가진 평면쉘 요소로, 말뚝은 보-기둥 요소로 모델링하여 전면기초와 결합하였다. 또한 말뚝두부 및 지반의 강성은 <TEX>$6{\times}6$</TEX> 강성행렬로 모델링 하였으며, 전면기초-말뚝-지반의 상호작용은 비선형 하중전이함수를 이용하여 선형/비선형거동의 모사가 가능하도록 하였다. 기존의 단순해석기법, 유한요소해석 및 현장계측값과의 비교 분석 결과, 본 해석기법이 대단면 말뚝지지전면기초에서 말뚝의 축하중 분포와 침하량을 비교적 정확히 산정하는 것으로 판단되며, 이러한 검증을 토대로 실제 대단면 기초설계에 대한 적용 가능함을 확인할 수 있었다. A three-dimensional approximate computer-based method, YSPR (Yonsei Piled Raft), was developed for analysis of behavior of piled raft foundations. The raft was modeled as a flat shell element having 6 degrees of freedom at each node and the pile was modeled as a beam-column element. The behaviors of pile head and soil were controlled by using <TEX>$6{\times}6$</TEX> stiffness matrix. To model the non-linear behavior, the soil-structure interaction between soil and pile was modeled by using nonlinear load-transfer curves (t-z, q-z and p-y curves). Comparison with previous model and FEM analysis showed that YSPR gave similar load-displacement behaviors. Comparison with field measurement also indicated that YSPR gave a reasonable result. It was concluded that YSPR could be effectively used in analysis and design of piled raft foundations.