Piled Raft Foundation Research Articles

Mechanical behaviour of piled-raft foundations subjected to high-speed train loading

In this paper, settlement of piled-raft foundation for high-speed train is considered systematically. It is observed in a case study that the railway settled significantly due to the cyclic train loading after a one-month trial operation. As traditional methods such as empirical methods or numerical simulation based on primitive constitutive models are unable to properly interpret the settlement mechanism, a sophisticated model-based numerical simulation, using a soil-water coupled finite element (FE)-finite difference (FD) hybrid algorithm, is conducted to investigate the mechanism of the settlement of the piled-raft foundation and excess pore water pressure (EPWP) of soft soils caused by the cyclic train loading. In order to demonstrate the performance of this numerical simulation, the calculated results are compared with the data recorded in the one-month trial operation and the reliability of the proposed numerical method is confirmed. The newly proposed numerical method is also used to predict the long-term settlement and the change in the EPWP during a one-year period. The predicted results suggest that without proper treatment, more serious settlement would have occurred, which is unacceptable in engineering terms.

Model load tests on battered pile foundations and finite-element analysis

Behaviours and resistance mechanisms of pile groups and piled rafts with or without batter piles were investigated through a series of load tests on foundation models at 1g field. Three-pile pile foundation models were used in the experiments. Dry silica sand having a relative density, Dr, of ∼82% was used for the model ground throughout the experiments. A series of triaxial CD tests of the sand were carried out to characterise the sand behaviour. Close-ended model pipe piles having a length of 255 mm and an outer diameter of 20 mm were used in the foundation models. The results of the load tests are presented and discussed in detail, focusing mainly on the horizontal load tests. Numerical analyses were conducted for cases of the piled rafts subjected to horizontal load to confirm the experimental results and to get a deeper insight into the resistance mechanisms of the piled raft foundations. It is shown from the results that the foundations with batter piles have advantages over the foundations with only vertical piles in aspects of resistance and settlement reduction.

Behaviour of model pile foundations under dynamic loads in saturated sand

In Japan and Turkey, predominantly traditional design concept of pile group is still adopted even though most pile foundations are piled raft foundations in reality. This situation may be attributed to the still limited knowledge about behaviour of piled rafts subjected to the combination of static and dynamic loads. Hence, in this study, a series of shaking table tests on 3-pile piled raft and 3-pile pile group models were carried out in saturated sand at 1-g field under the combinations of static vertical and dynamic horizontal loading, where the input motion was sinusoidal wave having a frequency of 20 Hz and 1.50 and 6.00 m/s2 amplitudes. The results showed that, raft-model ground contact in piled raft is very effective to reduce settlement compared to pile group even in liquefied soil. Moreover, even in piled raft, the horizontal resistance reduces if liquefaction of the ground surface occurs, due to the loss of the raft base resistance.

Hybrid Approach for Rigid Piled-Raft Foundations Subjected to Coupled Loads in Layered Soils

Abstract This paper proposes an efficient hybrid approach for analysis of the responses of piled-raft foundations subjected to coupled loads (combination of vertical loads, horizontal loads, and moments) in layered soils. The proposed method comprehensively accounts for pile–pile, pile–soil surface, soil surface–pile, and soil surface–soil surface interactions. Moreover, to capture the influence of embedment and active/passive effects of piles, a modified Vesic’s subgrade modulus for embedded piles and passive piles was adopted. To avoid a large number of time-consuming integration processes, the shear displacement method and elastic foundation beam method were employed to calculate the vertical and horizontal responses of a single pile, respectively, and the results were then extended for the pile group. The results calculated with the proposed method for piled-raft foundations in layered soils were found to have good agreement with those obtained from the more rigorous finite-element methods (FEMs) and ...

MECHANICAL BEHAVIORS OF PILED-RAFT FOUNDATION AND DIAPHRAGM WALL IN DEEP EXCAVATION OF TAIPEI METROPOLITAN

The piled-raft foundation has been widely used in recent years to solve the low bearing capacity and the excess settlement problems of the raft foundation on the soft soil. The soft soil is reinforced by the pile and behaviors of the diaphragm wall and the raft are also modified by the pile. However, effects of the pile on the diaphragm wall and the raft have not been fully discussed in the past. In this paper, a finite element program, Plaxis-3D, is used as the numerical simulation tool. First, simulations of pile loading tests are performed to verify the input parameters and models. Then, deep excavation cases with and without the pile group in a typical Taipei Metropolitan soil profile are modeled and discussed to identify effects of the pile. Results show that the pile lowers the lateral displacement of the diaphragm wall, reduces the influence zone of ground settlement around the excavation area and modifies the deformation pattern of the diaphragm wall and ground settlement.

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.

Soil-Structure Interaction of a Piled Raft Foundation in Clay – a 3D Numerical Study

Piled raft foundation designs consider the contribution of the pile cap in transferring load to the ground and distributing load over the piles. The concept of a piled raft foundation requires a comprehensive evaluation of a number of factors that affect the performance of the foundation system. In this research the interaction among piles, pile cap and soil of a piled raft system on medium and stiff clays was studied. The effects of various distances between piles (s/d) in affecting load transfer mechanisms and deformation were considered. The study was performed by utilizing the 3D finite element method with a professional software package called Plaxis3D Foundation. A case study of the piled raft foundation performances of a foundation design for a high-rise building based on the soil stratification in Jakarta was also performed and is presented in this paper.

Load sharing ratio of pile-raft system in loose sand: an experimental investigation

This technical note presents the results of a series of tests carried out on instrumented model pile-raft foundation to investigate the load sharing ratios between the foundation’s components where a loose sand layer is encountered near the ground surface. Four different pile-raft models with two different pile numbers and lengths were considered. In each model, the settlement of the raft and the load of each pile were monitored during the load application process. The experiments showed the effectiveness of pile length on reducing the overall settlement of the pile-raft system. The results showed also that the proportion of load transferred to any pile in a closely spaced pile group increases with its distance from the centre of the group. Unlike some previous studies that classified soil profiles containing loose sands near the surface as unfavourable situations for piled rafts, the experimental results herein represent an evidence of the efficiency of piled rafts even in soil profiles with loose sands immediately beneath the raft. Indeed, ignoring the contribution of the raft would lead to unnecessary over-conservatism in the design of piled rafts.

Numerical analysis of settlement and bearing behaviour of piled raft in Babol clay

Piled raft foundations are the composite construction of a spread foundation and a few number of piles that are usually used in soft soils to compensate the weakness of a raft in satisfying the design requirements. Due to the complex behaviour of piled raft, it is necessary to take into account a number of factors such as pile geometry and arrangement, raft thicknesses, soil properties and loading condition in the design. In this study, a parametric study has been conducted by a three-dimensional finite-element method considering the full interaction between the components of piled raft foundation. The underlying soil consists of Babol clay in drained condition with various stiffness and plasticity, determined from the results of a geotechnical investigation. The results of numerical analyses show that the bearing capacity of piled raft obviously increases with increasing pile length, pile spacing and raft thickness, especially in stiff clay. The effect of load type is more significant for the differential settlement and pile loads than other parameters. Finally, the advantages of using an optimum design method are examined in a special case of analyses and a case history.

지반조건이 Piled Raft 기초의 거동에 미치는 영향 평가를 위한 매개변수 연구

지반조건이 Piled Raft 기초의 거동에 미치는 영향 평가를 위한 매개변수 연구

Influence of Foundation Type on Seismic Performance of Buildings Considering Soil–Structure Interaction

In selecting the type of foundation best suited for mid-rise buildings in high risk seismic zones, design engineers may consider that a shallow foundation, a pile foundation, or a pile-raft foundation can best carry the static and dynamic loads. However, different types of foundations behave differently during earthquakes, depending on the soil–structure interaction (SSI) where the properties of the in situ soil and type of foundation change the dynamic characteristics (natural frequency and damping) of the soil–foundation–structure system. In order to investigate the different characteristics of SSI and its influence on the seismic response of building frames, a 3D numerical model of a 15-storey full-scale (prototype) structure was simulated with four different types of foundations: (i) A fixed-based structure that excludes the SSI, (ii) a structure supported by a shallow foundation, (iii) a structure supported by a pile-raft foundation in soft soil and (iv) a structure supported by a floating (frictional) pile foundation in soft soil. Finite difference analyzes with FLAC3D were then conducted using real earthquake records that incorporated material (soil and superstructure) and geometric (uplifting, gapping and [Formula: see text] effects) nonlinearities. The 3D numerical modeling procedure had previously been verified against experimental shaking table tests conducted by the authors. The results are then presented and compared in terms of soil amplification, shear force distribution and rocking of the superstructure, including its lateral deformation and drift. The results showed that the type of foundation is a major contributor to the seismic response of buildings with SSI and should therefore be given careful consideration in order to ensure a safe and cost effective design.

Development of Axial Pile Load Transfer Curves Based on Instrumented Load Tests

The load transfer method is an efficient and practical tool for the analysis of single piles and combined systems such as pile-raft foundations and rigid inclusions. The existing transfer curves rely either on the measurement of the pressuremeter modulus, which is not widespread at the international level, or they have been developed only for specific pile and ground types. In order to develop new transfer curves valid for all pile and ground types without the need of pressuremeter tests, a database of 50 instrumented pile load tests was examined. The existing curves were first compared to the measurements at the pile shaft and at the tip. Then the parameters of the most appropriate curve types, the cubic root and the hyperbolic curve, were calibrated in order to best match the measurements. A single set of parameters for each proposed curve type is suitable enough for most pile and ground types. The good agreement of the proposed curves was confirmed by applying them to assess the overall load-settlement curve of 72 other pile load tests.

Pile Spacing Optimization of Short Piled Raft Foundation System for Obtaining Minimum Settlement on Peat

Short Piled Raft is a modified piled raft foundation system, which represents combination between raft foundation and pile foundation, but the length of pile is relatively shorter. The basic concept of the Short Piled Raft foundation system considers the passive soil pressure creating a stiff condition of slab-pile system. This means that the thin concrete slab floats on the supporting soil, while the piles serve as stiffeners concrete slab and also to reduce settlement of the foundation. Slab to pile ratio of such system has been mentioned by several researchers, however the optimum pile spacing of stability performance for obtaining minimum settlement on peat haven't been clearly discussed. In this study, finite element method to simulate the stability performance related to settlement of Short Piled Raft foundation system was used. Short Piled Raft foundation system with concrete slab of 7.0 m x 7.0 m square was assumed to be built on peat with the thickness of 3.5 m. The material properties of pile and raft were constant. The outer diameter of galvanized steel pipe as pile was 0.30 m; raft thickness was considered to be constant of 0.15 m and the length of pile was 3.0 m, while the pile spacing varied from 0.50 to 3.00 m. Point load varied from 0 to 100 kN with increment of 20 kN was also considered as a static load, acted on the centre of the concrete slab. Optimization was done by comparing each numerical result of simulations, thus conclusion can easily be drawn. The optimum pile spacing was 1.00 m which produced minimum settlement of 30.11 mm under the load of 100 kN.

Evaluation of the existing piled foundation based on piled–raft design philosophy

Abstract Many well-documented case histories for conventionally designed large pile groups proved that this design approach is conservative and dramatically increases the cost of foundation without almost any benefit neither to geotechnical capacity of foundation nor to serviceability. Monitoring results of these case histories, especially in the case of floating piles, have shown low efficiency of pile capacity usage due to direct transfer of considerable part of the load to the supporting soil via the raft. In this paper, a proposed methodology for the combined-piled–raft design based on the conventional philosophy is applied to evaluate existing conventionally designed piled foundations of two identical residential towers located in Cairo, Egypt. The proposed methodology considers a conventional factor of safety for piles, and consequently, it does not violate the existing building codes. The three-dimensional finite-element analyses are performed to evaluate the load sharing between raft and piles. A detailed geotechnical investigation is carried out to obtain soil stratification and material parameters. The pile–soil interface parameters are obtained through back analyses of the available pile load tests. The results of the analyses show that the predicted geotechnical capacity of the combined piled–raft foundation system considering the conventional factor of safety for piles considerably exceeds the design capacity of the original conventional pile group.

Design and Field Monitoring of Piled Raft Foundations with Deformation Adjustors

AbstractThis paper presents a case study of applying a new device termed deformation adjustor in piled raft foundations to support a high-rise building. The deformation adjustors are mounted on a pile head to optimize load distribution of a piled raft foundation so that a relatively uniform foundation deformation can be achieved in complicated load, construction, and soil conditions. In this case study, the project site is located in a coastal city in China, featuring complicated subsurface soil conditions with abundant large boulders. The project was put on hold for a decade because in the complicated soil conditions the piles could not be installed to the required depths. The project resumed with introduction of deformation adjustors which helped to shift the applied loads from piles to subsoil below the raft and thus considerably reduced the pile lengths. This case study describes the preliminary design of pile-raft foundations with deformation adjustors, followed by a comprehensive monitoring program ...

3D Numerical Model for Piled Raft Foundation

AbstractLoad sharing of piled raft foundations is known as an economical design for deep foundations. Nevertheless, research in this area has been lagging because of the complexity of the problem and lack of field data. Numerical modeling can be used to provide valuable data with a high level of success. A three-dimensional finite-element model of a piled raft foundation was developed to simulate the case of a piled raft foundation. The model accounts for pile-to-pile, raft-to-pile, pile-to-soil, and raft-to-soil interactions. The model was used to examine the effect of the key parameters governing the performance of this foundation during loading and, accordingly, the load shared by the piles and the raft. After validating the numerical model with available data in the literature, the model was used to develop data for a wide range of parameters and to examine the role of the foundation geometry, including pile spacing in the group, pile length, pile shape, pile diameter, and raft thickness. Furthermore,...

Numerical simulation on the seismic absorption effect of the cushion in rigid-pile composite foundation

In order to quantitatively study the seismic absorption effect of the cushion on a superstructure, a numerical simulation and parametric study are carried out on the overall FEA model of a rigid-pile composite foundation in ABAQUS. A simulation of a shaking table test on a rigid mass block is first completed with ABAQUS and EERA, and the effectiveness of the Drucker-Prager constitutive model and the finite-infinite element coupling method is proved. Dynamic time-history analysis of the overall model under frequent and rare earthquakes is carried out using seismic waves from the El Centro, Kobe, and Bonds earthquakes. The different responses of rigid-pile composite foundations and pile-raft foundations are discussed. Furthermore, the influence of thickness and modulus of cushion, and ground acceleration on the seismic absorption effect of the cushion are analyzed. The results show that: 1) the seismic absorption effect of a cushion is good under rare earthquakes, with an absorption ratio of about 0.85; and 2) the seismic absorption effect is strongly affected by cushion thickness and ground acceleration.

Analysis of piled raft coefficient and load-settlement on sandy soil

A piled raft foundation is a combined foundation, which is developed to utilize the load-carrying capabilities of both raft and piles. To obtain an optimum piled raft design, it is important to properly evaluate and consider the load-sharing behavior between the raft and piles, which changes according to the settlement level of the piled raft. In this study, 27 three-dimensional finite element models were analyzed to investigate the piled raft coefficient with linear and nonlinear load-settlement behaviors. The length of piles was varied between 10, 15, and 20 m. The spacing between pile centers was varied between 3D, 5D, and 7D, and the pile diameter was kept constant. The number of piles and the distance between the exterior piles and the edge of the raft were maintained at 9 and 1 m, respectively. The sand conditions varied between dense, medium, and loose. The results indicated that the piled raft coefficient increases when the load-settlement curve is linear and decreases when the load-settlement curve is nonlinear. The influence of the incremental increase in pile length on the piled raft coefficient is more pronounced in short piles than in longer piles. The raft thickness has a negligible effect on the piled raft coefficient.

Effect of in-situ variability of soil on seismic design of piled raft supported structure incorporating dynamic soil-structure-interaction

Inherent variability of soil considerably affects the seismic design of piled raft supported structures. Conventional design of such structure adopts fixity at base level of superstructure and pile head. However, soil–pile–superstructure interaction largely affects the fundamental frequency and design forces in columns and piles. In contrast, fixed base assumption cannot capture soil structure interaction (SSI) effect. In addition, uncertainty in soil may further leads to a change in the dynamic behavior of the system. This study examines the effect of inherent variability of undrained shear strength of soil in seismic design of structures supported by piled raft foundation embedded in soft clay. Superstructure is modeled as lumped mass stick model and piled raft slab is modeled as rigid plate. Pile is modeled as Euler–Bernoulli beam element and soil resistance is modeled using linear Winkler springs attached to the pile. Dynamic analysis is carried out in time domain to estimate the responses. Monte Carlo simulation technique is used for probabilistic assessment of the fundamental frequency and forces at column and pile attributing a wide range of parametric variation of a representative soil–piled raft–superstructure system. The study shows that the fundamental frequency and forces in column and pile changes significantly due to soil variability.

PROBLEMS IN RECONSTRUCTION OF PILE-RAFT FOUNDATION

In practice, in many cases using combination of piles and large-slabs could be observed technological and structural defects before the start of their operation. These defects are dictated by the complex interaction between piles system and thin raft slabs. In order to establish the causes of defects can be imposed a wide range of studies covering research on the ground, the reinforced concrete structural elements and materials (piles and raft), the technology performance and others. In this study in order to identify the causes of defects are used a series of research methods for determining the properties of materials, environmental conditions and computational models to describe the interaction between ground and upper structure. With this set of methods are established causes and selected measures for appropriate reconstruction. The scope of these measures consists in the use of a combination of hardening by injection of the ground under the contact base of raft. With grouting the aims are to improve the skin friction and end bearing resistance of the piles. In the complex decision are sought the approaches to keep the completed structures-piles and raft. The focus of this work is to improve the interaction of the pile-raft system and ground base at the expense of reducing the load on piles. In this case, the geological formation, represented by Paleogene sediments with alternating layers of hard clay and clay sandstones largely supports the realization of the design measures.