Pile Foundations In Liquefiable Soils Research Articles

Assessing the impact of inertial load on the buckling behavior of piles with large slenderness ratios in liquefiable deposits

Pile foundations used in liquefiable deposits often have large slenderness ratios, and these piles are particularly vulnerable to earthquake-induced soil liquefaction and occur buckling instability under axial load alone as soils around the pile liquefy. However, insight into the precise impact of inertial load on the buckling behavior of piles in liquefiable deposits is still lacking, and the current methods used to calculate the critical buckling load of the pile in liquefiable ground usually ignore inertial load. In light of the above, two shaking table tests were carried out to clarify the impact of inertial load on the buckling behavior of piles partly embedded in saturated sands. Moreover, a novel calculation method considering inertial load was presented to accurately estimate the critical buckling load of the pile in liquefiable deposits. The feasibility of the presented method had been verified using the results from a centrifuge experiment and an analytical method along with a finite element method. Furthermore, parametric analysis was conducted to study the effect of soil type, peak ground acceleration (PGA), pile diameter, and unsupported length ratio on the critical buckling load of the pile in liquefiable soils. Finally, comparing the calculated results of critical buckling load between the method presented in this paper and the method in the design code confirmed the limitation of the current design code. These combined analyses demonstrate that the critical buckling load of the pile decreases due to the action of inertial load, resulting in the pile being more susceptible to buckling failure. Therefore, designers have to consider the impact of inertial load during the seismic design of pile foundations in liquefiable soils.

Seismic response and failure modes analysis of pile foundations in liquefiable soils using various design criteria

Pile foundations may fail by bending, shear forces and buckling etc., if soil surrounding the pile liquefies during earthquake. In this paper, a detailed 3D numerical model was developed based on the Showa Bridge that collapsed during the Niigata earthquake, estimations have been made of the times that the Showa Bridge collapsed based on a soil and pile seismic response. Then, seismic design criteria of pile foundations corresponding to different failure modes are selected, it is found that the pile of Showa Bridge may have fail by buckling. Furthermore, the effects of the pile flexural rigidity, earthquake type, peak ground acceleration, and degree of soil layer liquefaction on the ground and pile response in liquefiable soil are examined. The peak bending moment of pile and pile top displacement increases with increasing degree of soil layer liquefaction. Finally, evaluates those criteria by comparing and contrasting the results in various conditions. Nonlinear discriminant methods considering the effect of pore pressure distribution can identify different failure modes with higher reliability compared to those obtained by linear theories., and suggested flowchart of evaluating bearing capacity of pile in liquefiable soils was purposed It is recommended that develop a more comprehensive theory of pile foundation failure discrimination.

A Simplified Approach of Design Pile Foundation on Liquefiable Soil in India

In India piles are designed as per IS 2911:2010 (Part 1) for different soil conditions considering all the load criteria. But there is no such provision in Indian Standard Codes for designing piles in potentially liquefiable soils. In this paper, the design of pile foundation in liquefiable soil is discussed. The provisions for design of pile foundations in liquefiable soil from different codes of practice from different countries are studied and the design approaches for the same are discussed based on those studies (Puri et al. 2008). The load bearing capacity of a pile in liquefied soil and non-liquefied soil is made based on the force equilibrium approach. A standardize graph which may be useful for practicing engineers has been plotted. Further, a comparative study is made based on the force equilibrium approach in Indian conditions.

Buckling analysis of pile foundation in liquefiable soil deposit with sandwiched non-liquefiable layer

Many past earthquakes have shown failure of structures with pile foundations attributed to liquefaction. Various experimental tests have also shown that buckling is one of the credible reasons for the failure of such pile foundations, which gets insignificant lateral support due to seismic liquefaction of surrounding soil. In nature, liquefiable and non-liquefiable soil can occur in alternate layers. However, while estimating the buckling capacity of a pile, there are no specific guidelines available, to the best of the author's knowledge, to reasonably estimate its buckling capacity considering the effect of sandwiched non-liquefiable layer. Some studies recommend to ignore the sandwiched non-liquefiable layer present within a liquefiable deposit and consider it as a full liquefiable layer, which can become too conservative in many situations when both the strength and the depth of non-liquefied sandwiched soil layer are high.In the present work, a rational method of estimating the buckling capacity of pile foundation in liquefiable soil with a sandwiched non-liquefiable layer is proposed through a detailed numerical investigation. The developed numerical model (using Beam on Non-linear Winkler Foundation approach) is validated against the centrifuge results. The model considers the initial imperfection of pile and material nonlinearity of pile and soil. The P-delta effect is also considered in the analysis. Detailed parametric study for major influential parameters on the buckling capacity of the pile foundation has been considered in terms of (a) sandwiched non-liquefiable soil layer's type, thickness, and position, (b) pile length above the ground level, and (c) liquefiable soil's initial relative density and thickness. Based on this study, an effective length factor (β) has been introduced, which can be easily used in standard Euler's buckling equation to find out the buckling capacity of the pile in such layered soil profile. A simple chart has been developed for β, and a step-wise methodology has been proposed with explanatory examples for the estimation of buckling capacity of pile foundation in liquefiable soil having sandwiched non-liquefiable layer, with reference to various influential parameters.

Numerical analysis for the vertical bearing capacity of composite pile foundation system in liquefiable soil under sine wave vibration

Composite pile foundation has been widely used in ground engineering. This composite pile foundation system has complex pile-soil interactions under seismic loading. The calculation of vertical bearing capacity of composite pile foundation is still an unsolved problem if the soil around piles is partially or completely liquefied under seismic loading. We have completed indoor shaking table model tests to measure the vertical bearing capacity in a liquefiable soil foundation under seismic loading. This paper will use a numerical approach to analyze the change of this vertical bearing capacity under seismic loading. Firstly, the Goodman contact element is improved to include the Rayleigh damping. Such an improvement can well describe the reflection and absorption of seismic waves at the interface of soil and piles. Secondly, the Biot’s dynamic consolidation theory incorporated an elastoplastic model is applied to simulate the soil deformation and the generation and accumulation of pore water pressure under seismic loading. Thirdly, after verification with our indoor shaking table test data, this approach is used to investigate the effects of pile spacing on liquefaction resistance of the composite pile foundation in liquefiable soil. The time histories of pore water pressure ratio (PPR′) are calculated for the liquefiable soil and the vertical bearing capacity in partially liquefied soil is calculated and compared with our indoor shaking table test data at the 3D, 3.5D, 4D, 5D and 6D cases (D is the pile diameter). It is found that the pile spacing has some influence on the extent of soil liquefaction between piles. The vertical bearing capacity varies with liquefaction extent of inter-pile soil. The optimization of pile spacing varies with liquefaction extent. These results may provide some reference for the design of composite pile foundation under seismic loading.

Shaking table test study on seismic performance of inclined pile foundations in liquefiable soil

Inclined pile foundations are widely used in civil engineering by virtue of sufficient horizontal stiffness, but few studies have touched upon the seismic performance of inclined piles in liquefiable soil. To better understand the performance of the inclined piles in liquefiable soil under earthquake conditions, a series of 1 g shaking table tests of inclined and vertical piles in liquefiable soil were performed. Superstructure-pile-soil dynamic interaction was considered while three types of earthquake waves with different characteristics were selected as the applied earthquake motions. The horizontal acceleration of the superstructure and the pile cap, the rotational acceleration of the pile cap, the total base shear force, and the bending moment of two types of physical models were monitored and analyzed. The results show that inclined piles in liquefiable soil can effectively reduce the horizontal vibration of the superstructure and the pile cap, and the acceleration reduction of the pile cap is about 2.5 times larger than that of the superstructure. Meanwhile, inclined piles can also reduce the total base shear force, and the extent of reduction depends on the input earthquake wave. Besides, the results suggest that the maximum bending moment of inclined piles is located at the pile head, and its value is positively correlated with the amplitude of the earthquake wave, and is affected by the type of the input earthquake wave. Overall, inclined pile foundations show satisfactory seismic performance for a superstructure-foundation-liquefiable soil system, and this study, with a rich amount of data, can serve as an important reference for the seismic design of inclined piles in liquefiable soil.

Kinematic Response of Pile Foundations in Liquefiable Soil of Indo-Gangetic Basin During Earthquake

Indo-Gangetic Basin (IGB) lying toward south of the Himalayas formed of deep alluvial layers is tectonically very active. It experienced some great earthquakes in past and signs of liquefaction had been reported by previous researchers. Understanding of deep alluvial deposit impact and liquefaction phenomena on response of pile foundations under seismic loading is of immense importance. This paper presents linear as well as nonlinear analyses of pile foundations of approach viaduct of a rail–road bridge near Patna situated in the liqueafiable soil of IGB. The above study was based on the parameters obtained from both field and laboratory tests. Six synthetic earthquakes of different magnitudes and peak ground acceleration were considered. A comprehensive state-of-the-art approach of determining kinematic response of pile foundation (considering liquefaction) using finite element method has been presented. A series of analyses were conducted such as free field ground response analysis, eigenvalue analysis for finding modes of vibration and dynamic linear and nonlinear time history analysis using HHT-α (Hilber, Hughes and Taylor) implicit direct method. Mohr–Coulomb criteria and UBCSAND model were used in this analysis. In linear analysis, liquefaction could not be simulated. However, in nonlinear analysis it could be done successfully, because the dynamic nonlinear analysis method has capability to perform investigation in the required strain range of liquefaction and lateral spreading.

Flexural Response of Pile Foundation in Liquefiable Soil Using Finite-Difference Formulation Following Pseudostatic Approach

The collapse of pile-supported structures, especially in liquefiable soils, is still a major concern to the geotechnical earthquake engineers. In the last few decades, extensive research has been carried out to analyse the behaviour of pile foundations under seismic conditions. However, there are only a few codal provisions that take into account the effects of liquefaction and liquefaction-induced ground movement considering the developments made so far. The prime objective of this paper is to stipulate a simplified methodology to assess the flexural response of a pile foundation under liquefied ground conditions considering the latest developments. In this study, a finite-difference-based formulation is devised to analyse the flexural response of a single pile foundation. The formulation is capable of evaluating the performance of the pile foundation under both the inertial and kinematic loading conditions through the pseudostatic approach. The implemented formulation has been validated with the established theoretical method, field test results and one past case history. Moreover, a detailed systematic investigation is presented for the evaluation of the flexural response of a single pile foundation embedded in a liquefiable site in Patna city, India, considering recently developed bending and buckling criteria in tandem. It is highlighted in the study that the bending and buckling collapse mechanism may be avoided by suitable selection of geometric configurations of pile ignoring the frictional resistance in the liquefaction zone.

Case Studies of Liquefaction-Induced Damages to Two Pile-Supported River Bridges in China

Pile supported river bridges still continue to collapse after most major earthquakes in the event of liquefaction. The identified failure mechanisms of piles in liquefied soil are: bending failure due to the inertial loads of the superstructure and kinematic loads due to the lateral spreading of soil; shear failure due to shear loads; buckling instability failure due to vertical loads and associated imperfections; settlement failure due to loss of effective stress in the liquefied zone and finally failure due to the effects related to the elongation of natural period of the piers (also referred to as dynamic failure). This paper revisits the collapse of Shengli Bridge (due to 1976 Tangshan Earthquake) and Panshan Bridge (due to 1975 Haicheng Earthquake) based on the aforementioned failure mechanisms. It has been concluded that pile supported bridges in liquefiable soil can collapse due to each of these five failure mechanisms or due to a suitable combination thereof. It is therefore quite imperative to design pile foundations in liquefiable soil by taking all the failure mechanisms into consideration. The simplified calculation procedure presented in this paper can also be used to carry out the design of bridge piles in the liquefiable soil.

Influence of site-specific soil amplification on seismic response of piles in liquefiable soils

Kolkata city in eastern India is spread along the banks of Hooghly River in a north–south direction and having typical alluvial soil which is generally soft and thick in nature. The city is situated in seismic zones III and IV and is an implication of moderate to high seismic risk. Hence in the present study, the influence of ground response analysis and subsequent soil amplification in the design of pile foundations in liquefiable soils is thoroughly discussed. One-dimensional equivalent linear ground response analysis of Kolkata city is conducted using SHAKE2000 computer program and 1989 Loma Gilroy, 1995 Kobe, 2001 Bhuj and 2011 Sikkim motions being the chosen input ground motions. The spectral acceleration at a damping ratio of 5% is seen to be 0.41 g, while the amplification factor of maximum horizontal acceleration is found to be 2.98 when 2001 Bhuj motion is the selected earthquake motion. The high magnitudes of soil amplification are attributed to the alluvial soil in maximum parts of the city. The analysis is further extended to earthquake resistant analysis of pile foundation embedded in liquefying and non-liquefying soil strata and exposed to combined loadings. The maximum bending moment is noticed at the boundary of the liquefying and non-liquefying soil layers with the depth of liquefying soil layer being almost 65% of total pile length. The importance of deflection and bending moment of the pile foundation as important parameters in seismic analysis of deep foundations is portrayed in the current study. The present results and design charts can be used by engineers for designing pile foundations against earthquake forces.

An investigation of the influence of near-fault ground motion parameters on the pile’s response in liquefiable soil

The performance of a soil-pile system can be significantly influenced by ground motion parameters. However, few research efforts have been performed to provide a complete description of the influence of key ground motion parameters on the pile’s behavior in liquefiable soil. In this study, a three-dimensional finite element (FE) model, incorporating a multisurface plasticity solid-fluid fully coupled formulation soil constitutive model, is developed and calibrated based on centrifuge test data. Seventy-two near-fault non-pulse-like (NF-NP) and seventy-two near-fault pulse-like (NF-P) ground motion records are studied with the calibrated FE model to distinguish the effects of several common ground motion parameters soon afterwards. Base on the parametric study results, a simple index, RPGV/PGA (i.e., the ratio of peak ground velocity (PGV) to peak ground acceleration (PGA)), shows its capability on characterizing the pile behavior under both NF-NP and NF-P ground motions. Furthermore, two equations are developed to characterize the relationships between the RPGV/PGA as well as the maximum pile’s moments and displacements. In general, this study can be helpful to gain new insights on the influence of typical index parameters for near-field ground motions on the response of the pile foundation in liquefiable soil.

Impact of Ground Response Analysis on Seismic Behavior and Design of Piles in Kolkata City

Kolkata city is a major metro city of eastern India and spread in a north–south direction along the east bank of the Hoogly river with the soil being predominantly soft, thick and alluvial in origin. According to seismic code of India, Kolkata city is located along the boundary of seismic zone III and IV which indicates moderate to high seismic hazard. In this paper, using derived empirical correlations between shear wave velocity V s and SPT N values, soil site classification is carried out and it indicated CLASS E category, highlighting the seismic hazard of Kolkata city. The alluvial nature of soil located in Kolkata city is prone to soil amplification when subjected to different earthquake motions at the bedrock level and amplification factor for bedrock level acceleration varying between 1.7 and 2.5 is obtained in the present study. The spectral acceleration at 5% damping ratio is observed to be 1.94 g, when subjected to 1995 Kobe earthquake motion. The results obtained from ground response analysis is used for seismic design of pile foundations passing through liquefiable and non-liquefiable soil strata by considering both kinematic and inertial loading. The maximum bending moment is observed to occur at the interface of liquefiable and non-liquefiable soil layers. Both bending moment and pile head deflection showed a substantial increase in magnitude when inertial loads are considered in the analysis in addition to kinematic loading. Hence the present study illustrates the significance of deflection and bending response of pile foundations in liquefiable soil as important parameters for seismic design of pile foundations in Kolkata city.

Lateral response of pile foundations in liquefiable soils

Liquefaction has been a main cause of damage to civil engineering structures in seismically active areas. The effects of damage of liquefaction on deep foundations are very destructive. Seismic behavior of pile foundations is widely discussed by many researchers for safer and more economic design purposes. This paper presents a pseudo-static method for analysis of piles in liquefiable soil under seismic loads. A free-field site response analysis using three-dimensional (3D) numerical modeling was performed to determine kinematic loads from lateral ground displacements and inertial loads from vibration of the superstructure. The effects of various parameters, such as soil layering, kinematic and inertial forces, boundary condition of pile head and ground slope, on pile response were studied. By comparing the numerical results with the centrifuge test results, it can be concluded that the use of the p-y curves with various degradation factors in liquefiable sand gives reasonable results.

Seismic Requalification of Pile Foundations in Liquefiable Soils

Pile-supported structures founded on liquefiable soils continue to collapse during earthquakes despite being designed with required factors of safety against bending due to lateral loads and axial capacity (shaft resistance and end-bearing). Recent research identified a few weaknesses in the conventional design approach: (a) when soil liquefies it loses much of its stiffness and strength, so the piles now act as long slender columns, and can simply buckle (buckling instability) under the combined action of axial load and inevitable imperfections (e.g. out-of-line straightness, lateral perturbation loads due to inertia and/or soil flow). In contrast, most codes recommend that piles be designed as laterally loaded beams; (b) Natural frequency of pile supported structures may decrease considerably owing to the loss of lateral support offered by the soil to the pile and the damping ratio of structure may increase to values in excess of 20 %. These changes in dynamic properties can have important design consequences. The immediate need is not only to rewrite the design code to incorporate these effects, particularly buckling instability but also to requalify and, if necessary, strengthen the existing important piled foundations in liquefiable soils. This paper aims to provide a methodology for carrying out requalification studies. A practical example is taken to show the application of the methodology.

Numerical simulations of shake-table experiment for dynamic soil-pile-structure interaction in liquefiable soils

A shake-table experiment on pile foundations in liquefiable soils composed of liquefiable sand and overlying soft clay is studied. A three-dimensional (3D) effective stress finite element (FE) analysis is employed to simulate the experiment. A recently developed multi-surface elasto-plastic constitutive model and a fully coupled dynamic inelastic FE formulation (u-p) are used to model the liquefaction behavior of the sand. The soil domains are discretized using a solid-fl uid fully coupled (u-p) 20-8 noded brick element. The pile is simulated using beam-column elements. Upon careful calibration, very good agreement is obtained between the computed and the measured dynamic behavior of the ground and the pile. A parametric analysis is also conducted on the model to investigate the effect of pile-pinning, pile diameter, pile stiffness, ground inclination angle, superstructure mass and pile head restraints on the ground improvement. It is found that the pile foundation has a noticeable pinning effect that reduces the lateral soil displacement. It is observed that a larger pile diameter and fixed pile head restraints contribute to decreasing the lateral pile deformation; however, a higher ground inclination angle tends to increase the lateral pile head displacements and pile stiffness, and superstructure mass seems to effectively influence the lateral pile displacements.

A New Method for Dynamic p-y Curves of Pile-Cap Structure in Layered Soil

Lateral dynamic response of pile foundation in liquefiable soil has been one of the focal problems of the geotechnical engineering field and varieties of test methods are put forward by experts and scholars. In the dissertation, a shaking table test is based on and a new calculation method is involved too. It’s the first time that using Fiber Prague Grating (FBG) technology in the method of study on lateral dynamic response of pile foundation in liquefiable soil. Experimental results indicate that calculation by method of FBG is more accurate than that by acceleration integral method. Data processing shows that p-y curve of pile foundation in liquefiable soil can be better to indicate the actual dynamic constitutive relation, and it establishes the theoretical basis of experimental study and engineer application of pile foundation in liquefiable soil

Study on Lateral Dynamic Response of Pile Foundation in Liquefiable Soil by Using FBG Method

The study on lateral dynamic response of pile foundation in liquefiable soil is a significant part about seismic damage. In this paper, a new data acquisition system of FBG and calculation methods is used in the small shaking table test. The results show that FBG method used in this test is proved to be efficient and acceptable in both time characteristics and precision characteristics, it may be widely applied in the future doubtlessly. What’s more, the characteristics of p-y curves in different peak accelerations are discussed. And varying of maximum stress and displacement by corresponding acceleration is discussed. A contrast about p-y curve between dry sand and saturate sand is related, which provides a new direction in research about p-y curve.

Probabilistic pseudo-static analysis of pile foundations in liquefiable soils

This paper presents the development, implementation, and application of a probabilistic framework for the pseudo-static analysis of pile foundations in liquefied and lateral spreading soils. The framework allows for rigorous consideration and propagation of the large uncertainties regarding quantification of seismic loads and soil–pile interaction relationships, which exist in the pseudo-static method. Building upon previous relationships proposed by others, the key features of the presented framework are outlined. In particular, the uncertainty estimation of the induced lateral soil displacements; superstructure inertia loads; and stiffness and strength of the liquefied soils are discussed in detail. The results of applying the pseudo-static method to a case study bridge structure are compared to that obtained using a rigorous seismic effective stress analysis within a similar framework. It is illustrated that the consideration of uncertainties in the pseudo-static framework provides enhanced communication of the foundation's seismic performance to end-users, and that the pseudo-static method provides seismic performance prediction consistent with that obtained using advanced seismic effective-stress analyses.

Seismic response of pile foundations in liquefiable soil: parametric study

The performance of pile foundations in liquefiable soil subjected to earthquake loading is a very complex process. The strength and stiffness of the soil decrease due to the increase in pore pressure. The pile can be seriously destroyed by the soil liquefaction during strong earthquakes. This paper presents the response of vertical piles in liquefiable soil under seismic loads. A finite difference model, known as fast Lagrangian analysis of continua, is used to study the pile behavior considering a nonlinear constitutive model for soil liquefaction and pile–soil interaction. The maximum lateral displacement and maximum pile bending moment are obtained for different pile diameters, earthquake predominant frequencies, Arias intensities, and peak accelerations. It is found that the maximum lateral displacement and the maximum pile bending moment increase when the predominant earthquake frequency value decreases for a given peak acceleration value.

Effective stress analysis of piles in liquefiable soil

When evaluating the seismic performance of pile foundations in liquefiable soils, it is critically important to estimate the effects of cyclic ground displacements on the pile response. Advanced analyses based on the effective stress principle account for these effects in great detail by simulating the process of pore pressure build-up and associated stress-strain behaviour of soils. For this reason, the effective stress method has been established as a principal tool for the analysis and assessment of seismic performance of important engineering structures.
 In this paper, effective stress analysis is applied to a case study of a bridge pier founded on piles in liquefiable soil. The study examines the likely effects of liquefaction, cyclic ground displacements and soil-structure interaction on the bridge foundation during a strong earthquake. A fully coupled effective stress method of analysis is used to compute the dynamic response of the soil-pile-bridge system. In the analysis, an elastoplastic deformation law based on a state concept interpretation is used for modelling nonlinear behaviour of sand. The seismic performance of the pile foundation is discussed using computed time histories and maximum values of ground and pile displacements, excess pore water pressure and pile bending moments. The advantages of the effective stress analysis are discussed through comparisons with a more conventional pseudo-static analysis of piles.