Pile Group Foundation Research Articles

基于阻抗函数的土-基础-风机支撑结构地震响应建模方法

A Chebyshev nested lumped-parameter model (LPM) was proposed to incorporate the frequency-dependent impedances into the time history analysis of soil-foundation-wind turbine systems. The complex Chebyshev polynomials were introduced to approximate the foundation impedances with the least squares curve-fitting technique. The computational program for seismic analysis of the system was developed based on the direct integration of the governing equation in the time domain. The validity and efficiency of the computational program were verified through the comparison examples. The time history analysis of a wind turbine supported by a pile group foundation under seismic excitation shows the universality and stability of the computational program. The advantage of the Chebyshev nested LPM is that it can express the frequency-dependent impedance accurately in the time domain and avoid the high-order numerical oscillation. The nested form of the model enables wider application to different kinds of foundations. In addition, as the present model adopts no mass unit, it avoids the problem of modifying the seismic loading at the node of the foundation and makes the analysis of practical engineering more convenient.

Assessment the effect of pile intervals on settlement and bending moment raft analysis of piled raft foundations

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.

3D dynamic analysis of the soil–foundation–superstructure system considering the elastoplastic finite deformation of both the soil and the superstructure

In this study, in order to investigate the effect of the nonlinearity of superstructure supported by group-pile foundation and liquefiable ground on the piles and surrounding ground soils, three-dimensional (3D) dynamic finite element analysis is conducted, in which the strong nonlinear behavior of both soil and structure is considered during earthquake loading process. In the calculation, RC pile is modeled by AFD model proposed by Zhang and Kimura (Soils Found 42(3):77–92, 2002), which can describe the axial-force dependent nonlinear behavior of RC piles properly and a sophisticate elastoplastic constitutive model proposed by Zhang et al. (Soils Found 47(4):635–648, 2007, Front Archit Civ Eng China 5(2):121–150, 2011) is adopted, which can properly describe density (overconsolidation), structured and stress-induced anisotropy of soft soil in a unified way under drained/undrained condition subjected to monotonic/cyclic loading. For superstructure, its mechanical behavior is described by three different 3D models, (1) a beam element theory proposed by Goto et al. (J Struct Eng 41A:411–420, 1995) that can take into consideration both the material and geometric nonlinearity; (2) trilinear beam that can roughly consider the material nonlinearity; (3) linear elastic beam. The main purpose of the research is to find out, the influence of not only the material nonlinearity, but also the geometric nonlinearity of the superstructure, with a unified calculating model in which the superstructure, the foundation and the soft are included. The calculated results show that the nonlinear behavior of superstructure has less influence on soft ground, but the large deformation of the superstructure may give rise to large extra moment of pier, which, as the results, will increase the external forces acting on the piles. Therefore, both the geometric and material nonlinear behavior of superstructure should be properly taken into consideration in seismic design, especially when it is built on a liquefiable ground.

Engineering geotechnical investigation for coral reef site of the cross-sea bridge between Malé and Airport Island

The Malé-Airport Island Cross-sea Bridge project is the largest island-linking project in Maldives, the country known as “the kingdom of coral reefs.” Coral reef is also a special type of rock and soil medium to support significant civil engineering projects. In the Cross-sea Bridge project, the engineering geotechnical investigation of the coral reef site was divided into two stages: the feasibility study and the construction-drawing design phase. Engineering geological survey techniques were applied, and together with field exploration methods, such as geophysical prospecting and drilling exploration, the geological conditions of the site with respect to bridge engineering demands were comprehensively evaluated. In addition, the design parameters for pile group foundations were proposed based on in-situ tests, such as standard penetration, dynamic sounding, and acoustic wave testing in borehole as well as laboratory physical and mechanical experiments and bearing-capacity tests for pile foundations using rock and soil samples drilled from the site. The investigative methods adopted in the Malé–Airport Island Cross-sea Bridge project and the results obtained will provide references for similar engineering projects in the future.

Joint earthquake, wave and current action on the pile group cable-stayed bridge tower foundation: An experimental study

Sea-crossing cable-stayed bridges located in areas of active seismicity are generally subjected to earthquakes, waves, current and other dynamic loads of potential threat during their service period. The pile group foundation, which is composed of bored piles and elevated pile caps, has been applied widely for pylons to ensure the stability of cable-stayed bridge towers. Owing to its large dimensions, complexity and marked three-dimensional characteristics, it is difficult to model the precise dynamic response of the pile group pylon foundation under the joint action of various dynamic loads by means of existing theory. In this paper, an experimental study is presented for a 1/100 scale dynamic test model of a bridge tower with a grouped pile foundation. The model was designed according to elasticity-gravity similarity laws and tested using the Earthquake, Wave and Current Joint Simulation System. The structural response of the bridge tower in air and water conditions with and without incident sine waves and current was investigated. The test results may be used for engineering practice and further research.

Modeling of safety evaluation of super-large deep-water group pile foundation

In order to make a reasonable security assessment for super-large pile-group foundation in deep water during the construction and operating period, a combination of safety monitoring technology and mathematical method was adopted as modeling the security assessment as per the existing observation results. Based on the analysis of the content of safety monitoring, we firstly fused various sensors to a single target state estimation. Secondly, according to the national standards, industry standards and the existing research and practice experience, we analyzed and determined the set of safety evaluation factor, simultaneously constructed the membership function of each factor with different characteristics and establish the weight of each one. Thirdly, we evaluated result by optimal decision fusion. It comes out that this model can be a good judge method for safety of Super-large pile-group foundation in deep water.

Simplified analysis of frame structures with viscoelastic dampers considering the effect of soil-structure interaction

In this study, simplified numerical models are developed to analyze the soil-structure interaction (SSI) effect on frame structures equipped with viscoelastic dampers (VEDs) based on pile group foundation. First, a single degree-of-freedom (SDOF) oscillator is successfully utilized to replace the SDOF energy dissipated structure considering the SSI effect. The equivalent period and damping ratio of the system are obtained through analogical analysis using the frequency transfer function with adoption of the modal strain energy (MSE) technique. A parametric analysis is carried out to study the SSI effect on the performance of VEDs. Then the equilibrium equations of the multi degree-of-freedom (MDOF) structure with VEDs considering SSI effect are established in the frequency domain. Based on the assumption that the superstructure of the coupled system possesses the classical normal mode, the MDOF superstructure is decoupled to a set of individual SDOF systems resting on a rigid foundation with adoption of the MSE technique through formula derivation. Numerical results demonstrate that the proposed methods have the advantage of reducing computational cost, however, retaining the satisfactory accuracy. The numerical method proposed herein can provide a fast evaluation of the efficiency of VEDs considering the SSI effect.

Model test of the group piles foundation of a high-speed railway bridge in mined-out area

The research on the mechanism of pile-soil-cap-goaf interaction and settlement of high-speed railway bridge located in mined-out area is still relatively rare. By taking the pile group of Guanshandi bridge foundation in Hefei- Fuzhou high-speed railway as the prototype, a model test is carried out. According to the similarity theory, the similar constant is derived and the similar model material is determined. Meanwhile, three types of data including the bearing behavior of piles, and the settlement law, and soil among piles are investigated. It can be found that: the influence of goaf on the bearing capacity of pile is inversely to the loading degree, the larger of loading degree, the smaller impact of goaf on the bearing capacity. There is no negative side friction can been found in pile body and the degree of downward tendency for the barycenter of side friction layout is obvious for piles in goaf. Although the bearing ratio of soil resistance under cap is relatively large, the cap effect is suggested be ignored considering the characteristic of goaf. There is a maximum critical value for the uneven settlement of pile group in goaf, and when the value is reached, the uneven settlement stop growing anymore. In addition, the formula for calculating bearing capacity and settlement of pile group in goaf based on test results, theory analysis and related standard is established.

3D dynamic finite element analyses and 1 g shaking table tests on seismic performance of existing group-pile foundation in partially improved grounds under dry condition

Pile foundations are commonly used for heavy superstructures in soft grounds. The failures of pile foundations have been reported in past major earthquakes. An economical and effective method for improving the seismic performance of existing pile foundations is the partial-ground-improvement method (PGI). The main concern of this method is how to determine the size and the location of the areas around a pile foundation to be improved. In this paper, numerical analyses and shaking table tests are conducted to find the optimum pattern for the PGI method. In the numerical analysis, the three-dimensional (3D) dynamic finite element method (FEM) is used with a unified system consisting of a ground, a group-pile foundation and a superstructure. Furthermore, the mechanical behaviors of the ground, the group-pile foundation and the superstructure are modeled by the Cyclic Mobility model, the axial force-dependent model, and the tri-linear model, respectively. With the above-mentioned numerical method, four different patterns of PGI are investigated and then an optimum pattern for the PGI method is proposed. All the numerical analyses are also confirmed by 1g shaking table tests. All the tests and the numerical analyses are conducted under dry condition.

Kinematic Bending Moments in Square Pile Groups

AbstractThis paper describes kinematic seismic interaction analysis of square pile groups in homogeneous soil deposits, focusing on bending moments induced by the transient motion. Analyses were performed by means of a three-dimensional (3D) numerical procedure able to account for both pile–soil–pile interaction and radiation damping. The seismic motion was defined by an artificial accelerogram at the outcropping bedrock, and one-dimensional (1D) propagation analyses were performed to define the free-field motion within the deposits. An extensive parametric study was conducted to determine the effects of different variables, such as the soil properties, the bedrock location, the number of piles, and the pile spacing, on the dynamic response of pile-group foundations. Bending moments obtained from the analyses of the pile group, both at the pile head and at the interface separating soil layers, were normalized with respect to the single-pile bending moments, allowing for the proposal of a new design formul...

Development of Graphical Method of Pile Group Foundation Design

In the construction projects, a pile group foundation is often utilized. The group of bored piles is usually installed relatively close to each other and joined at the top by a pile cap to hold up the loads. In other hand, a fast estimation of the groups of piles capacities are needed in the preliminary design and in other conditions of projects, such as a supervisor of projects want to estimate the capacities of the group of piles. The purpose of this research is to study the correlations of groups of piles efficiencies with the number of piles and to compare the groups of piles capacities with the single piles capacities. Furthermore, this study is aimed to make a fast estimation of groups of piles capacities using proposed graphical method.The piles efficiencies are calculated using several methods, such as Simplified Analysis, Converse-Labare [1][2], Los Angeles Group, Seiler - Keeney, Das, and Sayed - Baker. In order to calculate the groups of piles capacities, the capacities of single piles are needed. The singles piles capacities are taken from graphical method proposed by Djarwanti et al. (2015a and 2015b). Three graphical methods utilized are derived from the Briaud et al. (1985) , Reese and Wright (1977), and Reese O’Neill method. Moreover, the proposed graphical method is applied in the case study. The case study takes palace in Graha Indoland Condotel Inside Yogyakarta Construction Project.The pile efficiency graph is recommended for this research since the value of pile efficiency could be easily taken. The value of pile efficiency for Graha Indoland Condotel Inside using Simplified Analysis, Converse - Labare, Los Angeles Group, Seiler – Keeney, Das, and Sayed – Baker are 1,75; 0,89; 0,94; 0,99; 4,00; 1,56 respectively. Meanwhile the value of pile group capacity with the value of pile group efficiency more than 1, showed that the pile group capacity based on the efficiency is bigger than the one based on single down pattern.

Study of static lateral behavior of battered pile group foundation at I-10 Twin Span Bridge using three-dimensional finite element modeling

In this study, the static lateral behavior of a battered pile group foundation was investigated using three-dimensional finite element (FE) analysis. The FE model was used to simulate the static lateral load test that was performed during the construction of the I-10 Twin Span Bridge over Lake Pontchartrain, La., in which two adjacent bridge piers were pulled against each other. The pier of interest was supported by 24, 1:6 batter, 34 m long piles in a 6 × 4 row configuration. The FE model of the battered pile group was developed in Abaqus and verified using the results from the field test. The model utilized an advanced constitutive model for concrete, which allowed distinct behavior in tension and compression, and introduced damage to the concrete stiffness. The soil domain comprised of several layers in which the constitutive behavior of clay layers was modeled using the anisotropic modified Cam-clay (AMCC) model, and for sands using the elastic perfectly plastic Drucker–Prager (DP) model. FE results showed good agreement with the results of the lateral load test in terms of lateral deformations and bending moments. The results showed that the middle rows carried a larger share of lateral load than the first and the last rows. The pile group resisted a maximum lateral load of 2494 t at which the piles were damaged within a 6 m zone from the bottom of the pile cap. The edge piles carried larger internal forces and exhibited more damage compared to the inner piles. The soil resistance profiles showed that soil layering influenced the distribution of resistance between the soil layers. A series of p–y curves were extracted from the FE model, and then used to study the influence of the group effect on the soil resistance. The p–y curves showed that the group effect reduced the soil resistance in all rows, with the lowest resistance in the third row. Finally, the p-multipliers were calculated using the extracted p–y curves, and compared to the reported p-multipliers for vertical pile groups.

Numerical investigations of pile load distribution in pile group foundation subjected to vertical load and large moment

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.

Responses of Liquefiable Soils in Pile Group Foundations of Tall Buildings from Shaking Table Tests

The responses of liquefiable soils around pile group foundations of tall buildings to earthquakes were measured using acceleration arrays in shaking table tests. System identification techniques were used to analyze the measured accelerations and pore pressures and to calculate the shear stress and shear strain in the soil inside and outside the pile group of a 12-story building as well as the soil shear moduli and damping. The analysis shows that the calculated soil stiffness is similar to the stiffness determined using laboratory tests and that the soil damping is higher. It also shows that pore pressure buildup reduces the shear wave velocity and the soil stiffness.

DSSI analysis of pile foundations for an oil tank in Iraq

Seismic analysis and design of pile foundations in weak soil strata to support oil tanks are of great importance to geotechnical practitioners. This paper presents an actual field study and dynamic soil–structure interaction (DSSI) analysis for an oil tank foundation design in weak soil strata for the Kafza site in Iraq, which is located in a seismically active region. For the particular in situ soil profile, a pile group foundation is proposed comprising a 24·1 m dia. by 1·5 m thick pile cap connecting together 89 piles, each pile being 800 mm in diameter and 26 m long. The foundation system was modelled using the finite-difference-based geotechnical program Flac3D to carry out detailed DSSI analysis. Field pile load test data for a static analysis were used for validation of the Flac3D model. The outcome of a probabilistic seismic hazard assessment was used to estimate target input motions resulting in maximum bending moments of 114 kN.m and maximum settlement of 21·9 mm for piles under dynamic conditions. The results obtained, comprising total and differential settlements and bending moments, were used for the final design of the proposed pile foundation and can be used for similar practical applications.

A multiphase approach for evaluating the horizontal and rocking impedances of pile group foundations

A multiphase approach for evaluating the horizontal and rocking impedances of pile group foundations

Numerical analyses and shaking table tests on seismic performance of existing group-pile foundation enhanced with partial-ground-improvement method

Numerical analyses and shaking table tests on seismic performance of existing group-pile foundation enhanced with partial-ground-improvement method

Seismic Retrofit of Pile Group Foundation with Thickened Caps

The case studied in the paper proves that thickening the pile cap is an effective seismic retrofit alternative to strengthen a pile group foundation. Unlike the typical seismic retrofitting of foundation, the proposed method eliminates the need to drive long piles into existing bridge substructures, substantially reducing cost, construction time and traffic interruption. The method thickens the pile cap of the bridge foundation to engage with a larger quantity of soil when under the influence of seismic excitations. The additional friction provided by the surface of the concrete encasement helps to resist the overturning moment of the earthquake forces, while the passive pressure provided by the soil helps to resist lateral forces during earthquakes. The method is recommended for implementation in the freeway bridge retrofit project in Taiwan due to construction constraints. A successful retrofit requires existing piles in at least moderate condition, detailed construction sequences and installation of the encasement.

Seismic Material Properties of Reinforced Concrete and Steel Casing Composite Concrete in Elevated Pile-Group Foundation

Abstract The paper focuses on the material mechanics properties of reinforced concrete and steel casing composite concrete under pseudo-static loads and their application in structure. Although elevated pile-group foundation is widely used in bridge, port and ocean engineering, the seismic performance of this type of foundation still need further study. Four scale-specimens of the elevated pile-group foundation were manufactured by these two kinds of concrete and seismic performance characteristic of each specimen were compared. Meanwhile, the special soil box was designed and built to consider soil-pile-superstructure interaction. According to the test result, the peak strength of strengthening specimens is about 1.77 times of the others and the ultimate displacement is 1.66 times of the RC specimens. Additionally, the dissipated hysteric energy capability of strengthening specimens is more than 2.15 times of the others as the equivalent viscous damping ratio is reduced by 50%. The pinching effect of first two specimens is more obvious than latter two specimens and the hysteretic loops of reinforced specimens are more plumpness. The pseudo-static tests also provided the data to quantitatively assessment the positive effect of steel casing composite concrete in aseismatic design of bridge.

Erratum to: Effect of seabed slope on the pile behaviour of a fixed offshore platform under lateral forces

Fixed offshore platforms supported by pile foundations have to resist lateral loads due to wave and current forces. The response to environmental loads is strongly affected by the soil-structure (pile) interaction. Forces exerted by waves are the predominant lateral environmental forces governing jacket structure design, especially the foundation piles. The purpose of the present investigation is to perform a static wave analysis of a typical fixed offshore platform in extreme environmental conditions and to study the effects of the combined lateral and vertical loads on pile group foundations. The three-dimensional modelling and analysis of the offshore platform are carried out using the finite difference method. The present analysis is done under static conditions considering the structural and environmental loads at extreme environmental conditions, reaching the state of static equilibrium. A parametric study is done by varying the seabed slope to examine the differences in the soil-structure interaction behaviour of piles. The lateral displacement at the pile top and at the seabed level increases with the seabed slope. Also the depth at which the maximum shear force and bending moment occur from the pile top increases with the seabed slope.