Investigating the seismic isolation effect of the cushioned pile raft foundation in soft clay through dynamic centrifuge tests

doi:10.1016/j.soildyn.2020.106554

Soil Dynamics and Earthquake Engineering

Volume 142, March 2021, 106554

https://doi.org/10.1016/j.soildyn.2020.106554 Get rights and content

Highlights

•
Centrifuge tests were performed for the seismic isolation effect of Cushioned-PR on earthquake.
•
The isolation effect of Cushioned-PR becomes significant with the increase in the magnitude of the earthquake load.
•
The interposed layer has a significant impact on the propagation of inertial loading and interaction between soil and piles.
•
The nonlinear performance and the isolation effect mechanism of Cushioned-PR are investigated.

Abstract

Cushioned pile-raft foundation (Cushioned-PR) is a new type of foundation for sea-crossing bridges in deep water (more than 50 m in depth). Cushioned-PR is able to tolerate a certain amount of slide that occurs between the raft and the piles under strong earthquakes. This characteristic could reduce the seismic motion transmitted to the superstructure to maintain the integrity of the bridge. Thus, Cushioned-PR has become popular for bridges under the threat of strong earthquakes. However, the dynamic responses of the Cushioned-PR under various earthquake intensities in soft clay have not been thoroughly understood. It is essential to better evaluate the isolation effect of Cushioned-PR to improve the design. In this study, the non-linear behavior of Cushioned-PR and the isolation effect of its interposed layer are evaluated using centrifuge tests. A series of dynamic centrifuge tests are performed with a 3 × 3 pile group foundation embedded in soft clay under different earthquake motions. Both the cushioned pile raft foundation system (Cushioned-PR) and the connected pile raft foundation system (Connected-PR) are tested in the centrifuge tests. Acceleration and residual displacement of the super-structure, and bending moment of columns and piles, are monitored during the experiments. The results show that the interposed layer in Cushioned-PR has a significant impact on the bending moment and residual displacement of the pile-raft system. Based on the observation from this study, the maximum bending moment of the column in the Cushioned-PR is around 28%–54% of the values from the Connected-PR. On the other side, the maximum horizontal displacement of Cushioned-PR is about 2–10 times larger than that of the Connected-PR. The results show that Cushioned-PR can effectively reduce the seismic excitation transmitted to the super-structure if the seismic intensity is high. However, the benefit of Cushioned-PR is marginal under low-intensity earthquakes.

Introduction

With great demands of transportation infrastructure due to economic growth, many bridges are under construction or planning, especially those wide crossing rivers or seas [21]. Generally, the connected pile raft foundation (Connected-PR) is recognized as an economical and sustainable foundation form and is widely used due to its promising performance [8], [11], [16], [20], [25], [28], [36], [37], [39]. This is because piles below the raft foundation can reduce settlement, which not only solves the problem of bearing deformation but also improves the stability and serviceability of a bridge [22]. Analytical methods have been proposed to calculate the bearing capacity and deformation of Connected-PR [6,28,40]. Further, centrifuge testing is performed to study the response of Connected-PR under pseudo-static and dynamic loading conditions [24]. The behavior of Connected-PR has been well documented. Although Connected-PR is a good solution in many cases, it has very limited tolerance of deformation. If the deformation exceeds a certain limit, Connected-PR could lead to catastrophic failure, for example, the accident of the Kobe line of Hyogoken-Nambu Earthquake [31].

In the seismic zones, earthquake is the major natural hazard leading to structural damage [2,4,12], where Connected-PR may not always be the best choice. A new foundation type has been proposed to overcome the deficiency of Connected-PR [7,35,45], whose piles are disconnected from the raft, namely the cushioned pile raft foundation system (Cushioned-PR). For Cushioned-PR, a cushion, typically a layer of granular materials, is located between the piles and the raft. The cushion can also be referred as the interposed layer. When a bridge with Cushioned-PR encounter an earthquake, the cushion is able to tolerate a certain amount of slide occurring between the raft and the piles under strong earthquakes. This way, Cushioned-PR can effectively reduce the seismic motion transmitted to the super-structure to maintain the integrity of the bridge [15,17,41].

Cushioned-PR is firstly applied in the Rion-Antirion bridge and has quickly become popular [23,33,34,45]. There has been a considerable amount of studies focusing on the performance of Cushioned-PR under static loadings. Previous researches suggest that the interposed layer could improve the overall performance and influence the static and dynamic characteristics of foundations [3,14,19,27,38,48]. Also, numerical simulations of the complex interactions between the components (raft, piles, and soil) of Cushioned-PR indicate the connection form of Cushioned-PR benefits the structure stability under dynamic load [43,44,46]. Previous studies have investigated the bearing capacity and settlement behavior of Cushioned-PR. Dynamic responses of Cushioned-PR are also studied by both experimental and numerical approaches [1,17,32]. Unfortunately, the vibration isolation effect of Cushioned-PR, especially Cushioned-PR in soft clay under dynamic loadings, has not been thoroughly understood [18].

This study aims to evaluate the vibration isolation effect of Cushioned-PR and its dynamic responses during seismic excitations in soft clay. A series of centrifuge tests are performed to investigate the dynamic response of both Cushioned-PR and Connected-PR in soft clay under different input motions. Parameters include acceleration, strain, and displacement are quantified and compared between the two types of foundation. The influences of the different peak base acceleration (PBA) and the earthquake waves are also analyzed through the Fourier transform and response-spectrum.

Section snippets

Centrifuge testing system

For centrifuge tests, the gravity field is simulated by increasing the centrifugal acceleration, and the actual problem is simulated by using the scale model [47,49]. In this study, centrifuge tests are performed on the centrifuge device (TLJ-150) in the Geotechnical Centrifuge Modelling Laboratory at Tongji University [29], as shown in Fig. 1. This device is able to reach a maximum centrifugal acceleration of 50 g, and a maximum vibration acceleration of 20 g. A customized laminar shear box,

Test results and discussions

In this section, the dynamic responses of Cushioned-PR and Connected-PR are analyzed and compared, including acceleration, bending moment, horizontal displacement, and vertical settlement.

Summary and conclusion

A series of centrifuge tests are conducted to compare the seismic responses of Cushioned-PR and Connected-PR to investigate the vibration isolation effect of Cushioned-PR. The synthetic ACCe100 wave, El-Centro wave, and Mexico City wave are employed to test the two types of foundations, respectively. The peak response acceleration of the super-structure, the natural period, and the natural frequency of the system, the horizontal and vertical displacement of the system, and the bending moment of

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (Grant No. 51878487). Financial support from these organizations is gratefully acknowledged.

References (51)

M.H. Baziar et al.
Effect of super-structure frequency on the seismic behavior of pile-raft foundation using physical modeling
Soil Dynam Earthq Eng
(2018)
K. Kawaguchi et al.
Several geotechnical design and construction issues with Akashi Strait Bridge
Soils Found
(2010)
A. Kumar et al.
Development of new prediction model for capacity of combined pile-raft foundations
Comput Geotech
(2018)
F. Liang et al.
Numerical analysis of composite piled raft with cushion subjected to vertical load
Comput Geotech
(2003)
G. Mylonakis
Simplified model for seismic pile bending at soil layer interfaces
Soils Found
(2001)
H. Rasouli et al.
A novel cushioned piled raft foundation to protect buildings subjected to naomal fault rupture
Comput Geotech
(2019)
J. Roy et al.
Natural frequencies of piled raft foundation including super-structure effect
Soil Dynam Earthq Eng
(2018)
F. Tradigo et al.
Non-linear soil–structure interaction in disconnected piled raft foundations
Comput Geotech
(2015)
F. Tradigo et al.
On the use of embedded pile elements for the numerical analysis of disconnected piled rafts
Comput Geotech
(2016)
J. Zheng et al.
Three-dimensional nonlinear finite element modeling of composite foundation formed by CFG–lime piles
Comput Geotech
(2008)

Y. Zhou et al.

Zhejiang University benchmark centrifuge test for LEAP-GWU-2015 and liquefaction responses of a sloping ground

Soil Dynam Earthq Eng

(2018)

J.D. Allmond et al.

Design considerations for rocking foundations on unattached piles

J Geotech Geoenviron Eng

(2014)

ASCE/SEI 41 Seismic evaluation and retrofit of existing buildings

(2014)

A.S. Azizkandi et al.

Load sharing and carrying mechanism of piles in non-connected pile rafts using a numerical approach

Int J Civ Eng

(2019)

S. Banerjee et al.

Seismic risk assessment of reinforced concrete bridges in flood-prone regions

Struct Infrastruct Eng

(2013)

A. Bhaduri et al.

Serviceability-based finite-element approach on analyzing combined pile–raft foundation

Int J GeoMech

(2020)

X. Cao et al.

Behavior of model rafts resting on pile-reinforced sand

J Geotech Geoenviron Eng

(2004)

P. Clancy et al.

An approximate analysis procedure for piled raft foundations

Int J Numer Anal Methods GeoMech

(1993)

C. Cui et al.

Effect of radial homogeneity on low-strain integrity detection of a pipe pile in a viscoelastic soil layer

Int J Distributed Sens Netw

(2018)

C. Cui et al.

Dynamic response of pipe pile embedded in layered visco-elastic media with radial inhomogeneity under vertical excitation

Geomech Eng

(2018)

R.P. Cunha et al.

Investigation of design alternatives for a piled raft case history

J Geotech Geoenviron Eng

(2001)

L. Deng et al.

Seismic design of rocking shallow foundations: displacement based methodology

J Bridge Eng

(2014)

M.G. Durante et al.

Experimental measurements of geotechnical system in 1-g tests[C]//Imeko Tc4 International Symposium & International Workshop on Adc Modelling & Testing Research on Electric & Electronic Measurement for the Economic Upturn

(2014)

V. Fioravante et al.

Contact versus noncontact piled raft foundations

Can Geotech J

(2010)

G. Gazetas et al.

Simple Methods for the Seismic Response of Piles Applied to Soil-Pile-Bridge Interaction. Third International conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics April 2-7

(1995)

Cited by (16)

Inertial and kinematic demands of isolated pile-supported wharves in liquefiable soils: Centrifuge tests
2024, Soil Dynamics and Earthquake Engineering
Pile-supported wharves in liquefiable soils are prone to severe damage during earthquakes. This study employs seismic isolation techniques to adapt for wharf construction, evaluating their seismic performance under lateral ground deformation due to liquefaction. Experimental and numerical analyses are necessary for confirming the efficiency of the isolation in decreasing the requirements for pile-supported wharves. The study initially tests two pile-supported wharves under geotechnical centrifuge conditions, one reinforced by isolation bearings and the other without. The objective is to simulate the force characteristics of isolated pile-supported wharves in liquefiable soils and to analyze the impact of isolation on reducing the seismic response of these wharves. Subsequent analysis delves into the interaction between inertia and kinematics for two types of pile-supported wharves, providing crucial insights. The development of plastic hinges for two kinds of pile-supported wharves under inertia and kinematics is also analyzed. Quantifiable thresholds are established to study the influence of isolation on the resistance of wharves to seismic disruptions, thus preventing pile-supported wharves damage.
Seismic isolation effect of unconnected piles-caisson foundation: Large-scale shake table tests
2024, Soil Dynamics and Earthquake Engineering
The seismic response and isolation mechanism of a new unconnected pile-caisson foundation (UPCF) suitable for supporting deep-water large-span bridges under seismic loading were investigated by large shaking table tests. Five scaled models were constructed utilizing different cushion material (aggregate), cushion thickness and piles configuration. Each model was tested under 18 different seismic loading conditions. The tests observations were analyzed to evaluate the seismic response characteristics and isolation mechanism of UPCF. The maximum displacement of UPCF and the peak acceleration of the input ground motion were linearly related. Under strong ground motions, the foundation soil and cushion displayed a significant softening behavior manifested in reduced natural frequencies and prolonged periods, which resulted in lower acceleration amplification. However, the stiffnesses of soil and cushion were largely restored after the ground shaking ended. The cushion model with larger aggregate particles performed better in terms of the caisson residual displacement and displacement restoration rate of the caisson. It was found that the UPCF constructed with a thin cushion layer comprised of large, rounded aggregate particles exhibited acceptable seismic isolation effect and reduced the peak seismic acceleration by up to 26.7%. It was also observed that the front and middle piles experienced larger loads, and accordingly, their peak moment envelopes were greater and the location of peak moment was shallower.
A 3D coupled ALEM-BEM method for assessing pile mitigation performance to moving-harmonic-load induced vibrations in cross-anisotropic porous saturated media
2023, Computers and Geotechnics
The present investigation aims at proposing a three-dimensional ALEM-BEM coupling analytical approach to evaluate the isolation effectiveness of pile barriers in stratified cross-anisotropic porous saturated media under moving harmonic loads. The governing equations of Biot’s porous elastic theory are decoupled through an analytical layer-element method (ALEM). The pile-soil boundary equation is derived using BEM combined with a two-stage theory. Two-node beam cells are adopted to discretize the piles based on Timoshenko beam theory. The pile barrier mitigation effectiveness is obtained depending upon a vibration screening theory. After carefully validating the presented solutions by various reduced instances, the impacts of two-phase compressibility, geomaterial cross anisotropy, and load frequency on the mitigation effectiveness are analyzed. Results illustrate that the isolation effectiveness is more sensitive to the velocity in the medium with high two-phase compressibility or low cross-anisotropic coefficient. The pile screening effectiveness influenced by a high-speed load is more sensitive to the frequency.
State-of-the-art review on responses of combined piled raft foundation subjected to seismic loads using static and dynamic approaches
2023, Soil Dynamics and Earthquake Engineering
Rapid urbanization and the unavailability of suitable ground conditions escalated the demand for high-rise superstructures over the years. Challenges persuaded geotechnical engineers to think of a robust yet economical foundation system that can support these superstructures without compromising their safety and serviceability. The combined piled raft foundation (CPRF) has been distinguished as an effective foundation that regulates the total and differential settlements and considerably improves the overall performance of the whole structure. Substantial pieces of research have been conducted previously to understand the responses of this robust foundation under static vertical loading. A few static loading code provisions are also available to help engineers to practice such foundation systems in real field conditions. In fact, many South-East Asia and European nations have appreciated the conceptualization of CPRF based on their worthwhile functioning reported in various on-field projects. However, design provisions for CPRF under lateral loading are still terse. The present paper, therefore, attempts to critically review contemporary research on the responses of CPRF under lateral loading in different subsoil strata and discusses the importance of soil-structure interaction (SSI) consideration in the seismic design of CPRF. The emphasis of discussion is oriented to several important design aspects of CPRF such as load-sharing, bending moment, peak acceleration, lateral and vertical deformation, period lengthening, etc. A few case studies on the performance of CPRF under seismic conditions are also discussed. The significance of such a study lies in framing constructive design guidelines of CPRF under lateral loading and resting in different subsoil conditions.
Effect of cushion types on the seismic response of structure with disconnected pile raft foundation
2023, Structures
In recent years, the benefits of reducing the impacts of the earthquake on the seismic response of disconnected pile raft foundation (DPRF) have simulated increasing research on this type of foundation to provide references for foundation design. One effective way to study the seismic response of soil-structures is to investigate the scaled models in 1-g shaking table tests. In this paper, a series of scaled 1-g shaking table tests were carried out to study the seismic response of scaled nuclear power stations with DPRF under earthquake excitations founded in clay. Three different cushion types were adopted to study their different effects on the seismic response of the structure and the foundation. The fundamental structural frequency, horizontal displacement, and acceleration results showed that cushion A with well-graded gravel and cushion B with a mixture of two gravel sizes were better than cushion C with a single gravel size. Although the cushion type had an insignificant influence on the bending moments of the disconnected piles, the maximum bending moments in all cases were found to be proportional to the near-pile acceleration. Furthermore, design engineers should pay more attention to the rocking of a structure with DPRF under earthquake loads.
A simplified approach for the response of pile groups composed of dissimilar piles
2021, Structures
Citation Excerpt :
However, it is difficult to apply the traditional load transfer approach directly to the analysis of the behaviour of pile groups. The pile interactions need to be considered in the analysis of load-settlement behaviour of pile groups [20–28]. The interaction coefficient, defined as the additional settlement at the pile top induced by the loaded neighbouring pile divided by the settlement under self-loading, was originally proposed by Poulos [23] to analyse the behaviour of pile groups.
In practice, saddle-shaped settlement is often investigated in the pile group foundation with identical piles. For the purpose of decreasing the differential settlement, uneven-distributed pile groups can be used. This paper provides a simplified approach to capture the behaviour of pile groups with dissimilar pile length or pile diameter. The hyperbolic function was adopted to express the mechanism of the interface between pile and soil. Considering the interaction of piles with dissimilar length, the hyperbolic load-transfer model of individual pile in pile groups composed of dissimilar piles were proposed. The related parameters of load transfer function of pile shaft or pile base of dissimilar piles were determined. To clarify the deformation mechanism of pile-soil system, an iterative approach for the analysis on the behaviour of non-uniformly arranged pile groups was proposed. Comparisons between the present computation results and the finite element simulation results were drawn to check the dependability of the proposed approach. Moreover, taking 3 × 3 pile groups as an example, the bearing characteristics of the centre pile, the edge pile and the corner pile in pile groups with different pile arrangements were analysed. For practical purposes, some suggestions on the pile groups composed of dissimilar piles were given to alleviate differential settlement among each individual pile and decrease the cost of pile groups and the construction difficulties.

View all citing articles on Scopus

View full text

Investigating the seismic isolation effect of the cushioned pile raft foundation in soft clay through dynamic centrifuge tests

Highlights

Abstract

Introduction

Section snippets

Centrifuge testing system

Test results and discussions

Summary and conclusion

Declaration of competing interest

Acknowledgments

Soil Dynam Earthq Eng

Soils Found

Comput Geotech

Comput Geotech

Soils Found

Comput Geotech

Soil Dynam Earthq Eng

Comput Geotech

Comput Geotech

Comput Geotech

Soil Dynam Earthq Eng

Design considerations for rocking foundations on unattached piles

J Geotech Geoenviron Eng

ASCE/SEI 41 Seismic evaluation and retrofit of existing buildings

Load sharing and carrying mechanism of piles in non-connected pile rafts using a numerical approach

Int J Civ Eng

Seismic risk assessment of reinforced concrete bridges in flood-prone regions

Struct Infrastruct Eng

Serviceability-based finite-element approach on analyzing combined pile–raft foundation

Int J GeoMech

Behavior of model rafts resting on pile-reinforced sand

J Geotech Geoenviron Eng

An approximate analysis procedure for piled raft foundations

Int J Numer Anal Methods GeoMech

Effect of radial homogeneity on low-strain integrity detection of a pipe pile in a viscoelastic soil layer

Int J Distributed Sens Netw

Dynamic response of pipe pile embedded in layered visco-elastic media with radial inhomogeneity under vertical excitation

Geomech Eng

Investigation of design alternatives for a piled raft case history

J Geotech Geoenviron Eng

Seismic design of rocking shallow foundations: displacement based methodology

J Bridge Eng

Experimental measurements of geotechnical system in 1-g tests[C]//Imeko Tc4 International Symposium & International Workshop on Adc Modelling & Testing Research on Electric & Electronic Measurement for the Economic Upturn

Contact versus noncontact piled raft foundations

Can Geotech J

Simple Methods for the Seismic Response of Piles Applied to Soil-Pile-Bridge Interaction. Third International conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics April 2-7