Rigid Pile Composite Foundation Research Articles

Method of settlement calculation for underlying layer of soft soil composite foundation based on load transfer mechanism

The mechanical properties of soil in soft soil area are poor, and the settlement of the underlying layer in the composite foundation accounts for a large proportion of the total settlement. At present, most of the research focuses on the settlement of the reinforced area, and the research on the settlement of the underlying layer is of great significance for the settlement of soft soil composite foundation. The differences in load transfer modes of soil and pile are analyzed, and based on the Boussinesq solution and Mindlin solution, a calculation method for the stress and settlement of the underlying layer in flexible and rigid pile composite foundation is proposed. The relative displacement of soil and pile in flexible pile composite foundation is small, and the negative friction can be ignored, but the influence of effective pile length should be considered. The relative displacement of soil and pile in rigid pile composite foundation is large, so the negative friction should be considered. Part of soil top stress is transmitted to the pile via negative friction, and then the pile axial force is transmitted back to the soil via positive friction. In addition to effective pile length, the change of stress transfer path caused by negative friction should also be considered in settlement calculation.

Retracted: 3D Finite Element Analysis of Seismic Response of Rigid Pile Composite Foundation with Microprobe Group

Retracted: 3D Finite Element Analysis of Seismic Response of Rigid Pile Composite Foundation with Microprobe Group

Study on Mechanical Properties of Composite Foundation with Rigid Pile Based on the Cushion and Strength Adjustor Control

Settlement of the pile ends in end-bearing rigid pile composite foundations is generally minimal, so only relying on the cushion to coordinate the pile soil deformation may result in insufficient deformation adjustment capacity. Using a deformation adjustor with a specific stiffness on the top of the pile is a method to coordinate pile–soil deformation, and the stiffness value of the deformation adjustor depends on the accurate calculation of soil deformation; however, the calculation of soil deformation is not mature at present. A new deformation adjustor based on strengths used in composite foundations is proposed, in which foam slabs with different yield strengths are placed on the top of the pile to coordinate the pile–soil deformation. Five tests are used to study the mechanical and deformation properties of a composite foundation with a foam slab. The test results show that when the stress at the top of the pile is less than the yield strength of the foam slab, the coordination of the pile–soil deformation mainly depends on the cushion. When the stress of a rigid pile exceeds the yield strength of foam concrete, the foam slab begins to yield and coordinate the deformation of pile and soil, and the settlement coordination ability of a rigid pile composite foundation with a foam slab is significantly improved. Finally, an engineering case is used to simulate the pile–soil stress sharing when the actual settlement is greater than the calculated settlement. The case analysis shows that the pile-top stress can be well controlled by the successive yielding of foam concrete slabs of different strengths, which reduces the influence of settlement error on the pile–soil stress sharing, and further promotes the engineering application of end-bearing rigid pile composite foundations.

Nonlinear optimization design of pile foundation based on settlement control principle

How to take certain measures to minimize the differential settlement of buildings is one of the urgent problems to be solved in the current pile-raft foundation design. In this paper, the nonlinear optimization design of pile foundation based on the principle of settlement control is developed. For the soil around the pile group, considering its nonlinear characteristics, when it yields, the ideal elastic-plastic model is adopted for calculation. Through numerical simulation, combined with the results of model test and field observation, some practical research results are obtained: the smaller the elastic modulus coefficient is, the flatter the load-settlement curve of CPF (Composite pile foundation) is, and the larger the fixed value is, the load-settlement curve is abrupt. Using settlement control to design rigid pile composite foundation has clear settlement. As a supplement to the insufficient bearing capacity of foundation soil, pile foundation makes full use of the bearing capacity of soil between piles. The design scheme is more economical, and it is a good nonlinear optimization method of pile foundation.

Calculation and Analysis of Nonlinear Algorithm for Stability of Nanosilica Powder Soft Soil Pile Foundation.

In order to reasonably evaluate the stability of the embankment supported by the rigid pile composite foundation, a nonlinear algorithm calculation and analysis method for the stability of the nanosilica powder soft soil pile foundation is proposed. First, the soft soil foundation reinforced by the composite structure of “piles (prestressed pipe piles, (cement fly-ash gravel, CFG) piles)—pile caps—geotextile pads” is analyzed through the soft soil embankment test section of the Wenfu high-speed railway. Second, the compressive modulus under one-dimensional confining compression is calculated using the layered summation method. Finally, the deep lateral deformation of the pile foundation soil is measured by an inclinometer to evaluate the actual displacement of the pile foundation soil. In the standard method, the empirical coefficient 1.1–1.7 is multiplied on the basis of the calculation result of this method to correct the calculation error. Combined with the test results, it is shown that nanosilica powder can give full play to its excellent characteristics: promoting hydration speed and hydration degree through the reaction of pozzolan refining and consuming Ca(OH)2 crystals produced by cement hydration. Soft soils and modified soft soils: a certain amount of nanosilica powder can significantly improve the strength of soft soil at different ages.

3D Finite Element Analysis of Seismic Response of Rigid Pile Composite Foundation with Microprobe Group.

In order to study the seismic performance of the rigid pile composite foundation, a three-dimensional finite element analysis of the seismic response of the rigid pile composite foundation with microprobe group was proposed. The three-dimensional finite element method is used to analyze the dynamic response law of pile group rigid pile composite foundation under the action of the earthquake, especially the internal force response of the pile body. It is worth noting that when the internal force response of pile decreases significantly, the maximum internal force of the whole pile is also significantly smaller than the maximum internal force of pile foundation. However, when the pile body is located on a layered foundation and the modulus of adjacent soil layers differs greatly, the earthquake action will cause the pile body to generate a large internal force. The seismic performance of the rigid pile composite foundation is feasible, and it can be extended and applied to the similar seismic performance test of other composite foundations.

Centrifuge study on behavior of rigid pile composite foundation under embankment in soft soil

The rigid pile composite foundation is widely used in highway projects in soft soil area as it can effectively increase the bearing capacity and stability of the foundation. While the research on the behavior and failure mode of rigid pile composite foundation under embankment is not enough, instability failure of rigid pile composite foundation often occurs in practical projects. This paper presents a centrifuge model test to investigate the load transfer mechanism, settlement characteristic and failure mode of rigid pile composite foundation under embankment. The test results show that: the soil displacement of different region in rigid pile composite foundation was different, obvious vertical displacement occurred in the soil under the center of embankment and the horizontal displacement was very small in this region; both vertical and horizontal displacement occurred in the soil under the shoulder of embankment; and obvious horizontal displacement occurred in the soil under the slope toe of embankment; moreover, ground heave also occurred near the slope toe of embankment. The soil displacement in rigid pile composite foundation had a large influence on the stress characteristic and failure mode of rigid piles, the compressive failure and bending failure would probably occur for the piles under the center and shoulder of the embankment, respectively, and the tension-bending failure would probably occur for the piles under the slope toe of embankment. The different failure modes of piles at different regions should be considered in the design of rigid pile composite foundation under embankment. The test results can be used to improve the design method for rigid pile composite foundation under embankment in practical projects.

Numerical analysis of bearing characteristics of composite foundation with variable diameter rigid pile

Variable diameter rigid pile composite foundation are proposed for the multi-layer foundation. The bearing characteristics of composite foundation with variable diameter rigid pile under vertical load are numerically calculated and analysed. The research content of this paper focuses on the variation law of load and settlement of composite foundation, pile axial force, pile lateral friction resistance and distribution law of soil internal force between piles under different diameter ratios etc. The results showed that Variable diameter of rigid pile composite foundation can effectively improve bearing capacity and control settlement and reduce the stress level of soil; negative skin friction section at the top of pile decreases with variable diameter ratio D/d increases, Zero skin friction section in diameter produced and increases with variable diameter ratio D/d increases; Optimal diameter ratio of pile in the variable diameter rigid pile composite foundation should be at about 1.75.

Analysis of settlement of existing buildings caused by unreasonable design of foundation

As for the settlement accidents of existing buildings, people pay more attention to the construction quality than the rationality of foundation design. This paper analyzes and discusses the problem of excessive settlement of existing buildings caused by unreasonable design based on three typical engineering cases. The conclusion is that as for the upper filled soil and lower soft soil foundation, the heavy tamping method is not suitable without auxiliary measures if the foundation settlement is strictly controlled; cement-soil mixing pile method is not suitable for high-rise buildings based on soft soil foundation; the foundation design should be based on deformation control when high compressibility soil layer exists, the pile body should penetrate the main compression deformation layer, and the pile end should fall on the good bearing stratum when using pile foundation or rigid pile composite foundation.

A quasi-equal strain solution for the consolidation of a rigid pile composite foundation under embankment loading condition

Based on the deformation characteristics of rigid pile, a quasi-equal strain assumption was proposed to analyze the consolidation properties of a rigid pile composite foundation. By considering the parabolic distribution of the horizontal permeability of the surrounding soil, the initial consolidation stress difference in the underlying stratum and the time and depth dependent additional stress, analytic solutions for the consolidation degree were derived. The analytical solution was compared to the numerical simulation obtained from the standard finite element method which validates the accuracy of the proposed analytical method. Furthermore, the factors that affect consolidation properties were systematically analyzed. The results show that the consolidation rate for a rigid pile composite foundation was slower than that for a composite foundation with a granular column but was more rapid than that for a natural double-layered ground. The consolidation rate increases with the relative reinforced depth, the permeability coefficient, the ratio of the constrained modulus of the pile to that of the surrounding soil, the ratio of the area replacement and the ratio of the constrained modulus of the cushion layer to that of the surrounding soil. The consolidation rate increases with the decrease in the loading period and the pile-end resistance coefficient.

Time Effects on Settlement of Rigid Pile Composite Foundation: Simplified Models

The behavior of pile composite foundation is studied using the flexibility method. During the analysis, determination of the flexibility matrix (settlement) is critical. However, conventional methods of Winkler and elastic half-space foundation models are incapable of considering the time effects of soil consolidation and creep. The foundation model of Zaretsky and Tsytovich [1965] can be used to evaluate settlement for unsaturated soils, but the complexity of numerical integration over an arbitrary loading area hinders its application. In this paper, a novel scheme is proposed for numerical integration by rotating the loading surface using the equiareal transformation technique. Therefore, a simplified closed-form solution is developed to calculate time dependent settlement for foundation soils. The efficacy of the proposed technique is demonstrated using illustrative examples of an elastic half-space, a rigid raft foundation without piles, and rigid pile composite foundations with multiple piles under surface loading. Furthermore, parametric study is conducted to evaluate the sensitivity of model parameters. The permeability [Formula: see text] and Poisson’s ratio [Formula: see text] are found to be important, whereas pore pressure coefficient [Formula: see text] and degree of saturation [Formula: see text] are less significant in the calculation.

A foundation treatment optimization approach study in hydraulic engineering

To reach a better foundation treatment project, an optimized analysis of composite foundation was studied in the field of hydraulic engineering. Its unique characteristics in hydraulic engineering were concluded. And, the overall and detailed analysis of the composite foundation model established was carried out. The index parameters of the vertical reinforced rigid pile composite foundation were formulated. Further, considering the unique role of cushion in hydraulic engineering, its penetration and regularity were analyzed. Then, comparative and optimized analyses of cushion multistage physical dimensions and multistage material characteristics were established. The parameters of the piles distance were optimized and the multilevel scientific and reasonable parameters information was obtained. Based on the information of these parameters, the practical application was verified. It effectively supported the effective application of vertical reinforcement rigid pile composite foundation in hydraulic engineering. The service mechanism of composite foundation was fully analyzed.

Numerical simulation on behavior of pile foundations under cyclic axial loads

On the basis of the two dimensional finite element analysis model, the pile foundations’ mechanical effect of the rigid pile composite foundation under the dynamic load was researched. Through the research, the development law and deformation property of axial force of pile body, shaft resistance of pile, and cumulative settlement of pile head under vertical cyclic dynamic loads were concluded. Through the comparison and analysis of the test results of dynamic models, the test results of Poulos (1989) and cumulative settlement model of the single pile under cyclic loads were confirmed. Based on the above research, Fortran language was adopted to introduce the soil attenuation factor, the secondary development of relevant modules of ABAQUS was carried out, and the effect of soil attenuation factor on dynamic property of pile-soil was discussed further.

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.

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.

Effect of Flexible Pile on Rigid Flexible Pile Composite Foundation with Geogrid Reinforced Cushion

Compared with pile-supported reinforced embankments, rigid-flexible pile composite foundation with geogrid reinforced cushion (RFPCFGRC) has its advantage of its economics. Piles play an important role in rigid flexible pile composite foundation with geogrid reinforced cushion. The bearing mechanics of RFPCFGRC is more complicated than that of pile-supported reinforced embankments because of addition of flexible piles. This paper discussed the diffence and the bearing mechanics of the two types of composidte foundation. The results show that addition of flexible piles has changed bearing mechanics of composite foundation and changes the load distribution among piles and soil. Soil arching degree of RFPCFGRC is larger than that of pile-supported reinforced embankments.

Character Analysis of Balance and Imbalance of Varying Rigidity of Rigid Pile Composite Foundation under Seismic Load

Based on ABAQUS finite element analysis software simulation, the finite element model for dynamic analysis of rigid pile composite foundation and superstructure interaction system is established, which selects the two kinds of models, by simulating the soil dynamic constitutive model, selecting appropriate artificial boundary.The influence of rigid pile composite foundation on balance and imbalance of varying rigidity is analyzed under seismic loads. The result shows that the maximum bending moment and the horizontal displacement of the long pile is much greater than that of the short pile under seismic loads, the long pile of bending moment is larger in the position of stiffness change. By constrast, under the same economic condition, the aseismic performance of of rigid pile composite foundation on balance of varying rigidity is better than that of rigid pile composite foundation on imbalance of varying rigidity.

Analysis of the Settlement in Rigid Pile Composite Foundation

On the basis of rigid pile composite foundation mechanism, This paper makes assumptions and establishes settlement calculation models, then applies shear displacement method to solve interaction flexibility coefficient of the pile-soil system and raises a rigid pile settlement calculation method, considering the effect of cushion.By calculating a certain experiment, it was found that theoretical and measured values of the relative error is smaller ,which can provide a reference for settlement calculation of rigid pile composite foundation in engineering.

The Analysis on Rigid Core Pile Composite Foundation Dynamic

Through studying the field test results of rigid core pile composite foundation, Analyzing dynamic characteristics and dynamic response from peak acceleration and frequency duration, peak velocity and seismic waves. The following conclusion were got: Along with the rising of the upper load, peak acceleration of rigid core pile decrease, The frequency of Rigid core pile was between 6Hz-44Hz, Peak rate in the bottom of core pile have obvious change.

Prediction of Composite Foundation Settlement Based on Multi-Variable Gray Model

In this paper, based on the principle of gray theory, MGM(1,n) multi-variable settlement prediction model was established. Combined with specific examples of projects, settlement of rigid pile composite foundation was predicted, and the prediction results are compared with both prediction results of GM(1,1) gray model which is currently comparatively mature and the settlement observation results. The study shows that it is effective to use MGM(1,n) multivariate gray model to predict composite foundation settlement.