Piled Raft Foundation Research Articles

Research on Construction Settlement of Different Soft Foundation

Vacuum preloading, rigid foundation, raft foundation and piled raft foundation are more commonly used in soft foundation treatment. PLAXIS is large finite element software of rock and soil, which can simulate the influence of different foundation forms. The settlement of the piled raft foundation is about 1/7 of the rigid foundation settlement, and it is the 1/2 of the raft foundation settlement.

AN ESTIMATING METHOD FOR LATERAL BEHAVIOR OF PILED-RAFT FOUNDATION

Some simplified design methods were proposed to predict behavior of lateral loaded piled-raft foundations on homogenous soil. One of them is the cone model method. However, only one average solution of pile behavior can be given by this method. It can’t evaluate the location factors of piles. Therefore, this paper describes a new simplified method to predict behavior of lateral loaded piled raft foundations covering the location factor of piles. At first, ground surface displacement is derived theoretically by Cerutti’s solution, then assuming that the raft foundation has rigid stiffness, these displacements are the same to calculation lateral loading distribution. Second, the ground displacement where pile placed could be estimated under calculated lateral loading. Third, the piles behavior are evaluated based on these lateral ground displacements. In addition, 3-D FEM numerical analysis were performed to compared with these solutions.

Settlement mechanism of piled-raft foundation due to cyclic train loads and its countermeasure

In this paper, numerical simulation with soil-water coupling finite element-finite difference (FE-FD) analysis is conducted to investigate the settlement and the excess pore water pressure (EPWP) of a piled-raft foundation due to cyclic high-speed (speed: 300km/h) train loading. To demonstrate the performance of this numerical simulation, the settlement and EPWP in the ground under the train loading within one month was calculated and confirmed by monitoring data, which shows that the change of the settlement and EPWP can be simulated well on the whole. In order to ensure the safety of train operation, countermeasure by the fracturing grouting is proposed. Two cases are analyzed, namely, grouting in No-4 softest layer and No-9 pile bearing layer respectively. It is found that fracturing grouting in the pile bearing layer (No-9 layer) has better effect on reducing the settlement.

Nonlinear analysis of flexible piled raft foundations subjected to vertical loads in layered soils

In this paper, a simplified nonlinear approach is proposed to study the behavior of flexible piled raft foundations. The flexible piled raft is modeled as a thin plate with the finite element discretization. By employing the load transfer method, a nonlinear finite differential formulation for the analysis of a single pile is created. Pile groups are analyzed by the superposition principle. The interaction factor between two piles is determined by considering the interaction between a receiver pile and the surrounding soil. Based on solutions for the stress and displacement in layered elastic half space, the interactions between pile and soil surface, soil surface and pile, as well as soil surface and soil surface subjected to vertical loading are also taken into account to determine the flexibility matrix of the pile group-soil system. In order to verify the validity of the proposed nonlinear analysis method, calculated results are compared with the numerical and test results from the literature. The good agreement achieved shows that the proposed method provides a simple and useful tool for engineering design.

Testing and Modelling of Concrete Pile Foundations

Foundation of building on concrete piles is often used when it is necessary to carry the load into larger depth as by common foundation. Bearing capacity of piles or piled raft foundation is wide area to research. This paper deals with experimental load test of concrete pile and with their numerical modelling. Several types of foundation construction were tested and two kinds will be presented and compared in this paper - reinforced concrete foundation slab and raft foundation (made of reinforced concrete foundation slab supported by drilled reinforced concrete pilot). These types of foundation constructions were constructed as models, in a reduced scale, approx. 1:10. The size had to be adjusted due to limited capacity of the testing equipment and financial reasons. Except measuring of the foundation behaviour, there was also carried out measurement of the adjacent terrain.The aim of this paper is to compare the behaviour of rigid slab and the piled raft. The measurement results will be then compared with the results of numerical modelling.

Behavior of Piled Raft Foundation Model Embedded within a Gypseous Soil Before and after Soaking

The paper explain an experimental study to show piled raft system behavior when embedded within gypseous soil in three different stats (dry, socking for 1 day and placing a bearing layer of dense sand below the gypseous soil when socking for 1 day). A small-scale “prototype” model of steel box with dimension of (60cm length x 60cm width x 75cm heights) was used for carried out the model tests. Two different lengths of reinforced concrete pile models (40cm and 45cm) of 2.0cm dia. were used to keep the same imbedded length ratio during testing piled raft and piles only. Three different configurations of pile groups (single, three and six piles) were tested in the laboratory in two ways, first; the raft does not contact with the soil and the second; the raft is in contact with the soil. In dry state, the gypseous soil showed a very high carrying capacity with reduction in settlement. Piled raft foundations show an efficient in dry state, where the load carrying capacity increased and the settlement decreased. The improvement ratios in the load carrying capacity were about 16% for single piled raft and 39% for group of three-piled raft, while settlement reduction ratios were about 18% for single piled raft and 45% for group of six-piled raft. When the gypseous soil socked with water for 1 day, the ultimate bearing capacity of foundations is generally reduced by about (69%-83%) compared with dry state for all model configurations. The improvement ratios in ultimate bearing capacity due to using piled raft in soaking state was about (11% -50%) whilst the reduction settlement ratios was about (16% -44%).

Settlement Analysis of Piled Raft Foundation System (PRFS) in Soft Clay

Settlement Analysis of Piled Raft Foundation System (PRFS) in Soft Clay

Vertical harmonic vibration of piled raft foundations in layered soils

SummaryThis paper develops a method to analyze the piled raft foundation under vertical harmonic load. This method takes into account the interactions among the piles, soil, and raft. The responses of the piles and raft are formulated as a series of equations in a suitable way and that of layered soils is simulated with the use of the analytical layer‐element method. Then, according to the equilibrium and continuity conditions at the piles–soil–raft interface, solutions for the piled raft systems are obtained and further demonstrated to be correct through comparing with the existing results. Finally, some examples are given to investigate the influence of the raft, pile length‐diameter ratio, and layering on the response of the piled raft foundations. Copyright © 2017 John Wiley & Sons, Ltd.

Nonlinear 3D interactive analysis of superstructure and piled raft foundation

An interactive design method that takes into account the coupling between the stiffness of the superstructure, the piled raft and the soil has been proposed for analyzing the response of building structure. Special attention is given to consideration of interaction between the superstructure and the piled raft. And a series of numerical analysis is performed to validate the interactive analysis routine in comparison to the unified analysis method. Through the comparative studies, it is found that the iterative and interactive analysis gave similar results of settlement and raft bending moment compared with finite element analysis. And it is also found that the proposed design method considering interaction between superstructure and foundation is capable of predicting reasonably well the behavior of building structures. It can be effectively used to perform the design of a superstructure-piled raft foundation system.

Soil–structure interaction in a combined pile–raft foundation – a case study

The present work explains the use of a piled-raft foundation in a raw materials storage building in South Bà Rịa–Vũng Tàu Province of Vietnam. The proposed foundation comprises an 81 m by 55·5 m raft that connects 581 precast hollow concrete piles 20 m long with 400 mm outer diameter. The proposal takes into consideration a specific in situ soil profile and a loading scenario. After the effectiveness of a single bay of the foundation had been checked, the entire foundation system was modelled using finite-element-based geotechnical software to enable a detailed soil–structure interaction analysis. Field pile load test data were used to validate the finite-element model. Various loading conditions, such as all compartments full to all compartments empty, were considered in the analysis. The results of the analyses indicate the importance of the raft in sharing 23–31% of the total vertical load. The results obtained – such as vertical settlement, differential settlement, tilt in the raft and axial load in the piles – were used in the final design. These results can also be used in similar practical applications.

ANALYSIS FOR AXIAL LOAD DISTRIBUTION IN PILE IN A PILED RAFT FOUNDATION STIFF CLAY BY FINITE ELEMENT

In this paper piled raft foundation has been analysed by nonlinear finite element method. The three dimensional nonlinear finite element analyses predict the actual behaviour of axial load distribution. The axial load variation is nonlinear for all the piles. For all pressure the element stress is more than the element stress. For any pressure the nodal deflection is maximum at top and minimum at bottom. Up to certain height the element stress is almost zero for all pressures. After that height the element stress increases with increase in height. The element stress increases with increase in pressure the measurement of axial load distribution in pile in field is very difficult and costly.

Evaluation of Piled Raft Performance Using a Verified 3D Nonlinear Numerical Model

The piled raft foundation system presents a feasible foundation option for high rise buildings. Piled raft foundations have a complex three-dimensional soil-structure interaction scheme including the pile-soil interaction, pile–pile interaction, raft-soil interaction, and finally the piles-raft interaction. Consequently, comprehensive 3D numerical models are sought to investigate this complex interaction. In this paper, a 3D finite element model was verified using published geotechnical centrifuge test results to further enhance the accuracy of the model. The study considered piled rafts installed in sand with stiffness that varies linearly with depth. A comprehensive parametric study was conducted to evaluate the effect of different foundation parameters including: pile diameter, pile spacing, raft width, and raft thickness on the overall behavior of the piled raft. The load carrying capacity of the piled raft and the load sharing mechanism between the raft and piles are evaluated. It was found that the load carried by piles is higher for rigid rafts (Kf > 600) due to the minimal interaction between the raft and subsoil compared to the relatively flexible rafts (Kf < 150). Moreover, the load transmitted by the raft increased by about 75% as the raft width increased from 4 to 7 m.

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.

Issues on Design of Piled Raft Foundation

Issues on Design of Piled Raft Foundation

Numerical simulations of the reuse of piled raft foundations in clay

The development and growth of urban environments in recent years is requiring geotechnical engineers to consider foundation reuse as a more sustainable solution to inner city redevelopment. Two main phenomena associated with foundation reuse have been reported in the literature, namely ‘preloading effects’ and ‘ageing effects’. The aim of this paper is to investigate the relative merits of these effects on the reusability of both piled and unpiled raft foundations in clay. Finite element analysis, in conjunction with an isotropic elasto-viscoplastic soil model, is employed for this purpose. The study is presented in two phases: (1) evaluation of preloading effects only by using a very low creep coefficient and (2) evaluation of combined preloading and creep effects. The variables considered in the parametric study include the number of piles, pile spacing, pile length, and soil type. Results show that both unpiled and piled rafts can exhibit significant capacity and stiffness increases upon reloading even for moderate levels of preload. Moreover, these increases are strongly dependent on the piled raft load sharing where unpiled raft and free-standing pile group capacity gains serve as upper and lower bounds, respectively, for that of a piled raft. This study underlines foundations reuse as an effective and sustainable solution for inner city redevelopment.

Experimental and Numerical Analysis of Piled Raft Foundation Embedded within Partially Saturated Soil

This paper presents an experimental and numerical study to investigate the load carrying capacity of piled raft foundation embedded within partially saturated sandy soil. The effect of matric suction on the bearing capacity of the foundation system was investigated. The experimental work consists of two models of foundation, circular raft foundation and circular piled raft foundation. The circular raft foundation has dimensions of 10cm in diameter, and 2.5cm thickness, while the piled raft foundation has the same dimensions of the circular raft model but with a single pile of 2.0cm in diameter and 40.0cm in length fixed at the center of the raft. Both models are loaded and tested under both fully saturated condition and unsaturated conditions, which are achieved by, predetermined lowering of water table. The lowering of water table below the soil surface was achieved in to two different depths to get different values of matric suction and the relationship between matric suction and depth of ground water table was measured in suction profile set by using three Tensiometers (IRROMETER). The soil water characteristic curve (SWCC) estimated by applying fitting methods through the software (SoilVision). A validation process then was carried out for the case of circular piled raft foundation with lowering the water table 45cm bellow soil surface in the aid of a sufficient finite element computer program ABAQUS 6.12. An eight-node axisymmetric quadrilateral element CAX8RP and CAX8R were used to simulate the soil continuum and piled raft respectively. The interaction method used to simulate the intersect surfaces of the system (pile-raft-soil) is a surface-to-surface discretization method under the concept of master and slave theory. The behavior of piled raft material is simulated by using a linear elastic model while the behavior of soil is simulated by an elasto-plastic model by the use of the Mohr-Coulomb failure criterion. The results of the experimental work demonstrate that the matric suction has a significant role on the bearing capacity of all tested models. It shows that the ultimate bearing capacity of circular raft foundation under a partially saturated condition is increases by about (7.0-8.0) times than the ultimate bearing capacity of fully saturated condition when lowering the water table 45 cm below the soil surface. While the ultimate bearing of circular piled raft foundation under partially saturated condition increases by about (8.0-9.0) times than the ultimate bearing capacity of fully saturated condition when lowering the water table 45 cm below the soil surface. The results of the ultimate bearing capacity of piled raft foundation that obtained from the experimental model and from the numerical modelling for the same soil condition and same matric suction indicate that a successful validation is achieved for the simulation process.

말뚝지지 전면기초의 실용적 근사해석법 개발

말뚝지지 전면기초의 실용적 근사해석법 개발

The experimental study of eccentric loading for piled raft foundations settling on slope crest

In this study, bearing capacities and settlements have been determined for a piled raft foundationsunder eccentric loading conditions. For this purpose, slope models which were safe against collapsing have been used. Pile raft foundations located in the sand have been fixed on slope crest. At experiments, poorly graded sand samples and steel piles have been used and the optimum value of the pile spacing from literature have been selected. For determining the effect of eccentric vertical loading for piled raft foundations, a series of experiments have been carried out to identify the contribution of the bearing capacity and settlement. As a result of this study, it has been determined important effect of eccentric vertical loading at piled raft foundations and design parameters have been proposed for basic engineering applications.

Analysis of the Load Sharing Behaviour and Cushion Failure Mode for a Disconnected Piled Raft

Disconnected piled raft (DPR) foundations are characterized by having no structural connection to a raft. The raft-pile gap is filled with a granular cushion, which creates a more uniform pressure distribution on the raft and reduces the differential settlement. A series of tests has been performed to investigate the load transfer mechanisms of a DPR. The effects of the thickness and stiffness of the cushion and the pile diameter are presented and discussed. A simple failure mode of the cushion is also put forward according to the cushion slip plane obtained by using the digital image correlation technique that tracks the pixels in the images and generates a displacement field. Then a new theoretical analysis has been presented for rigid pile composite foundation. Through comparative studies, it is found that the present method is validated as reasonable by laboratory tests and is in agreement with several current design methods.

Analysis and Prediction of Foundation Settlement of High-Rise Buildings under Complex Geological Conditions

Based on an example of a project in Tangshan, the high-rise buildings are built in karst area and mined out affected area which is treated by high pressure grouting, and foundation is adopted the form of pile raft foundation. By long-term measured settlement of high-rise buildings, It is found that foundation settlement is linear increase with the increase of load before the building is roof-sealed, and the settlement increases slowly after the building is roof-sealed, and the curve tends to converge, and the foundation consolidation is completed. The settlement of the foundation is about 80% - 84% of the total settlement before the building is roof-sealed.Three layer BP neural network model is used to predict the settlement in the karst area and mined affected area.Compared with the measured data, the relative difference of the prediction is 0.91% - 2.08% in the karst area, and is 0.95% - 2.11% in mined affected area. The prediction results of high precision can meet the engineering requirements.