Pile Stiffness Research Articles

Experimental investigation on load carrying capacity of hollow and composite pile materials in layered soil

Composite piles are widely used in geotechnical field for its mechanical and physical properties. Composite piles are usually filled with concrete. Although the use of composite pile is increasing, the proper design and its ultimate load carrying capacity are still under investigation. This research mainly aimed to study the behaviour of hollow pile and composite pile. Two types of model pile were prepared which are hollow pile and composite pile. The composite pile was made up of stainless steel. It was hollow steel pipe has outer and inner diameters of 13 mm and 10 mm respectively, filled with standard mortar. The pipe without filling mortar known as hollow pile. Different length-to diameter ratios of 10, 15, 20, 25 and 30 are considered by varying the pile length to simulate behaviour of stiff piles. Experiments were conducted on both hollow pile and composite pile embedded in layered soil under static axial load and static lateral load. Experiments results were validated with the results obtained from finite element software (ABAQUS). The experimental investigations and numerical analysis results indicated that increasing the L/d ratios increases the load carrying capacity and decreases the settlement in both the piles.

A Review on Effect of Pile Stiffness on Seismic Response of Structure

Abstract: Pile foundations are widely employed for a variety of structures on shaky ground. The importance of seismic design in ensuring the effective operation of a structure under severe seismic loading conditions cannot be overstated. For the analysis of seismic forces on a structure, IS 1893 will be employed. This research entails the choosing of a specific form of building structure. A comparison of buildings with and without pile foundations will be shown. Because of the differences in their properties, the seismic behaviour of the various structures differs. The influence of pile stiffness on the structure's seismic response will be investigated. The rigidity of the piling foundation could have an impact on the structure.With the rise in seismic activity, there may be a need for more efficient pile foundation design to withstand earthquake loads. The major goal of this study is to compare pile stiffness with changes in diameter and zone. Keywords: Pile Foundation, STAAD-Pro, Structure, Stiffness, zone, Pile Cap, Load Estimation, Pile cap, Pattern of Pile.

Analytical solutions of the dynamic response of a dual-beam model for a geosynthetic reinforced pile-supported embankment under moving load

To analyze the dynamic response of geosynthetic-reinforced pile-supported (GRPS) embankment, a dual-beam model that includes an upper Euler-Bernoulli beam under moving concentrated load and a lower Euler-Bernoulli beam to simulate pavement structure and geosynthetic reinforcement respectively are established in this paper. Furthermore, the embankment fill layer is idealized as continuous spring-dashpot systems supporting the pavement structure. The pile improved foundation is idealized as a series of periodically distributed pile-soil spring-dashpot systems supporting the geosynthetic reinforcement. The governing equations of the dual-beam system are derived based on the assumptions above. The steady-state solutions are solved by Fourier series and verified by periodicity condition and Finite Difference Method. A detailed parametric study has been performed to analyze the effects of load velocity, pile stiffness and reinforcement moduli. The results show that the deflection and stress distribution of GRPS embankment are related to the load location. The influence of load velocity on deflection and stress distribution cannot be ignored. The deflection and stress increase as load velocity increases. Increasing pile stiffness and reinforcement modulus can reduce the influence of load velocity on the GRPS embankment. Piles and geosynthetic reinforcement play a significant role in GRPS embankment deflection and making GRPS embankment more stable.

Load-sharing mechanism of piled-raft foundation: a numerical study

Responses of the piled-raft foundation are complex due to the combined working and the existence of load-sharing mechanism between piles and raft. A clear understanding of this mechanism leads to optimization of the design of the foundation. This paper presents numerical studies on the load-sharing mechanism characterized by the load-sharing ratio under using different numbers of piles and broad ranges of values of pile spacing, pile length, settlement of the piled-raft, and the depth of the raft base based on the finite element method constructed in PLAXIS 3D. The results show that the load-sharing ratio of the piled-raft increases significantly when increasing the value of pile spacing, the settlement of the foundation, and the depth of raft base, and decreasing the number of piles. This paper also introduces the stiffness modification ratios of piles and rafts. Interestingly, these stiffness modification ratios and the load-sharing ratio can be nicely collapsed on a master curve as a function of a dimensionless number which is defined as a ratio of pile stiffness and raft stiffness for each case of pile configuration. These scalings provide clear evidence for the unified description of the key parameters to control the load-sharing mechanism of the piled-raft foundation.

Response of pile groups in layered soil to dynamic lateral loads

This paper presents an analytical solution that provides the dynamic response of laterally-loaded pile groups with an arbitrary number of piles installed in layered soil. The solution allows modelling robustly pile-to-pile interaction effects via a new stress-based interaction factor, that considers the fact that soil displacements along the periphery of large-diameter piles of a group subjected to lateral loads will not be in-phase. Layered soil conditions are introduced in the solution by modelling wave propagation in the soil surrounding the piles with the popular plane-strain model and considering soil as viscoelastic material. These idealisations greatly simplify the formulation, at no expense of accuracy when considering loading of relatively stiff piles under serviceability conditions. The solution provides the Winkler modulus for each pile in the group as function of problem parameters that have direct phenomenological meaning, and allows direct calculation of the horizontal impedance of the entire pile group. The presentation concludes with results of a parametric analysis, to demonstrate the effect of considering layered soil conditions and the cross-sectional dimensions of the piles on the response of the group.

Seismic response of helical pile groups from shake table experiments

This paper presents and discusses the measured responses of single and grouped helical piles to strong ground motions during a large-scale shake table testing program. The effects of earthquake characteristics (i.e., intensity and frequency content) on the seismic performance of single and grouped helical piles are evaluated from the measured responses. In addition, the performance characteristics of helical pile groups are discussed in terms of the interaction between piles within a group and the contributions of vertical and lateral stiffness of individual piles to the rocking stiffness and the overall capacity of the pile group. Furthermore, the effect of pile head connection to the pile cap (fixed or pinned) on the pile group's response is evaluated and the responses of fixed pile groups (2-bolts connection) and pinned pile groups (1-bolt connection) are compared. Finally, the behaviour of a single pile and a pile within a group is compared in terms of their normalized responses.

Investigation on the behavior of hybrid pile foundation and its surrounding soil during cyclic lateral loading

With increasing demand and requirements for offshore wind turbines (OWTs) construction, research on the hybrid pile foundation is gaining increasing popularity. In this paper, a series of 1-g model tests are conducted to investigate the lateral behavior of monopile and hybrid pile foundations under one-way cyclic loading. The influence of pile stiffness, pile diameter for the hybrid foundation and hybrid foundation type on the lateral behavior of the structure is analyzed. To visualize particle movements during the loading process, several colored sand bands are arranged at ground surface around the structure. Continuous monitoring of sand surface during the loading process and excavation of sand sample reveal different particle migration patterns around different structures. Experimental results verify the superiority of hybrid foundation in resisting lateral loads and reducing accumulated lateral displacement. Based on the coupled discrete-continuum modelling of cyclic load tests, the deformation pattern of monopile and hybrid structure and the particle displacement contour at different sections are provided. The numerical results further point out the potential influence of the soil plug on the lateral capacity of the hybrid pile foundation, which could be the focus of future research.

Interaction Model for Torsional Dynamic Response of Thin-Wall Pipe Piles Embedded in Both Vertically and Radially Inhomogeneous Soil

The inhomogeneity of soil is a ubiquitous problem for pile foundations due to, for example, pile installation (radial inhomogeneity) or the natural sedimentation of soil (vertical inhomogeneity). Most continuum theory solves soil equations by artificially setting the displacement at the inner soil core as zero, which results in the misestimation of soil shear strength. Although the additional mass model avoids the utilization of artificial boundaries, the internal deformation of soil is overlooked. In this paper, the modified additional mass model is proposed. The capacity of this model is verified through comparison with former studies. Through a comprehensive parametric study, it was found that (1) the inhomogeneity of soil has significant influence on pile stiffness and damping amplitudes, (2) the length and strength of the pile would affect the resonance frequency of the soil–pile system, (3) only the soil within the range of 0.3r1 to the pile shaft has a visible effect on the dynamic response at the pile head.

Improved calculation of the rigidity of double-row piles and double-beam composite support and displacement analysis under different soil properties

As a new type of cantilever-type supporting structure, the double-row pile supporting combination system can improve the overall rigidity to maintain the safety and stability of the side of the foundation pit. The case of a double-row pile foundation pit support project in the Wanquan District of Zhangjiakou is taken as an example. Based on the existing double-row pile crown beam stiffness coefficient calculation method, the effect coefficient of the crown beam and the coupling beam is introduced to optimize and improve the effect of the coupling beam and the crown beam. The results show that (1) in the calculation of the double-row pile structure, the common lateral restraint effect of the crown beam and the connecting beam on the double-row supporting piles should be considered, and the rigid connection of the crown beam and the connecting beam should be taken as a whole to improve the rigidity coefficient of the double beam lateral support of a rectangular double-row pile. (2) The combined stiffness of the double-beam combined support system has a greater impact on the displacement of the pile top, and the displacement under a combined stiffness of 40-50 MN/m are close to the observed value. The calculated length of the crown beam and the introduced crown beam and connecting beam effect coefficient have a great influence on the combined stiffness of the double-beam composite support system. The combined stiffness decreases with the increase of the calculated length, and increases with the decrease of the effect coefficient. (3) The lateral support stiffness of the double-row piles under the double-beam composite support system is affected by the difference between the vertical and lateral displacements of the front and rear piles. The maximum lateral displacement of the front and rear piles is affected by the friction angle of the soil, the cohesion and the proportional coefficient of the horizontal resistance of the soil. Changing the tensile strength will not affect the displacement and deformation of the double-row piles. There is a displacement inflection point below the buried depth of the foundation pit and within the scope of the pile bottom. The displacement at the inflection point is equal under different friction angles and different cohesive forces.

Estimation of bending moment and pile displacement for soil-pile-quay wall system subjected to liquefaction induced lateral spreading

The liquefaction-induced lateral spreading has been responsible for severe damages on the pile foundation during major earthquakes. Therefore, the seismic response of soil-pile-quay wall systems in liquefiable soils still needs further investigations. In this paper, a three-dimensional (3D) nonlinear dynamic finite element (FE) analyses are used and developed for the coupled dynamic soil-water system considering the soil, pile, and quay wall interaction. The numerical analysis efficiency was verified by the data of a large-scale (1 g) shaking table experiment. A parametric study was also investigated on the model to clarify the effect of each parameter, such as pile stiffness, pile diameter, and pile length, under various peak ground acceleration. On this basis, the results obtained indicate the three factors have significant effects on bending moment and pile displacement. Furthermore, it is observed that the depth of liquefaction changes as the peak ground acceleration changes. Based on the dimensionless soil-pile interaction parameter, a simplified method is provided for predicting the maximum bending moment and the maximum pile displacement of the pile group subjected to liquefaction induced-lateral spreading.

Permanent accumulated rotation of offshore wind turbine monopile due to typhoon-induced cyclic loading

In order to study the effect of typhoons on the accumulated deformation of monopile foundations for offshore wind turbines, a series of 1-g laboratory model tests with a geometrical scale of 1:100 were carried out. Through the horizontal static and cyclic loading tests of a stiff pile embedded in a medium dense sand deposit, the relationship between the accumulated rotation of the pile and the number of loading cycles under different loading conditions was obtained. The results show that the final accumulated rotation is mainly caused by the typhoon load series and is not affected by the loading sequence. Based on these results, a method is presented to predict the accumulated rotation of the monopile foundation during its service life, and a case study of a 6 MW wind turbine supported by a monopile at a water depth of 30 m in sand is conducted by using the method. The results show that the permanent accumulated rotation of the monopile throughout the design life is mainly contributed by cyclic loading induced by typhoons and the contribution of cyclic loading with small amplitudes can be ignored.

Time-varying characteristics of the durability and lateral bearing behaviour of FRP bar-reinforced concrete piles in marine environments

In this paper, the time-varying characteristics of the durability and lateral bearing behaviour of fibre reinforced polymer (FRP) bar-reinforced concrete piles in marine environments are studied. A diffusion model of chloride ions in FRP bar-reinforced concrete piles is established based on Fick's second law. The failure probability of the corrosion initiation time of FRP bar-reinforced concrete piles induced by chloride attack is evaluated. The stiffness degradation model of FRP bar-reinforced concrete piles with different replacement ratios of FRP bars is established based on the time-dependent reinforcement corrosion model. The lateral bearing behaviour of FRP bar-reinforced concrete piles under lateral loading is obtained by the finite difference method. The Monte Carlo simulation method is used to generate random parameters to evaluate the failure probabilities of FRP bar-reinforced concrete piles under the failure criteria of bending moment and lateral displacement. The analysis results show that for the same FRP replacement ratio, the bending stiffness of FRP bar-reinforced concrete piles decreases with increasing exposure time, and the decreasing range of bending stiffness of FRP bar-reinforced concrete piles decreases with increasing FRP replacement ratio. For an exposure time of 50 years, the lateral displacement of the pile top increases with an increase in the replacement ratio of the FRP bars but decreases with an increasing replacement ratio of the FRP bars for exposure times of 100 years and 150 years. Before an exposure time of 75 years, the failure probability of FRP bar-reinforced concrete piles under the two failure criteria increases slightly with the increase in the replacement ratio of FRP bars but decreases significantly with the increase in the replacement ratio of FRP bars after an exposure time of 75 years.

Time-varying behavior of corrosion-damaged piles under cyclic lateral loading in marine environments

In this study, degradation models for pile and soil stiffnesses under cyclic lateral loading in marine environments are established. Based on the proposed models, the time-varying behavior of corrosion-damaged piles under cyclic lateral loading in marine environments is analyzed. The influences of the surface chloride concentration, number of cycles and cyclic load amplitude on the behavior of corrosion-damaged piles under cyclic lateral loading are investigated. The results show that the degradation rate of the pile stiffness speeds up with the increase in surface chloride concentration and that the attenuation coefficient of the soil stiffness gradually decreases with the increase in the number of cyclic lateral loads. The lateral displacement of the pile at the same depth increases with increasing exposure time and the number of cycles. The bending moment of the pile decreases with the deepening of the corrosion degree of the pile at the same pile depth. The position of the rotation center gradually moves down with the increase in the cyclic load amplitude. For the same exposure time, the lateral displacement of the pile top increases with increasing cyclic load amplitude, and the maximum bending moment of the pile increases with increasing cyclic load amplitude.

Influence of Surcharge Load on the Adjacent Pile Foundation in Coastal Floodplain

In this paper, in order to investigate the behavior of existing piles caused by the horizontal and compression deformation of soft substratum due to backfill surcharge on coastal floodplain, three-dimensional finite element models of piles adjacent to surcharge load were established. The deformation and migration law of soft soil was analyzed. The behavior of single pile and double row pile adjacent to surcharge load were studied, in which the influence of surcharge load location, surcharge pressure, pile stiffness, and pile top constraint conditions were considered. The results show that as the position of surcharge load is closer and the surcharge pressure increases, the response (e.g. deformation and bending moment) is more obvious. With the increase of pile stiffness, the range of passive load is increased. The deformation behavior of pile body under different constraints of pile cap is significantly different. The effect of secondary bending moment caused by pile axial force is obvious and cannot be ignored. If there is a thick soft substratum, it is beneficial to improve the behavior of adjacent piles by using cement mixing pile reinforcement.

Centrifuge testing on monotonic and cyclic lateral behavior of large-diameter slender piles in sand

The existing studies have been primarily focused on the lateral behavior of large-diameter stubby pile or small-diameter slender pile in sand, with little attention paid to large-diameter slender pile. This study presents a unique series of centrifuge tests on monotonic and cyclic lateral behavior of heavily instrumented large-diameter slender piles in medium dense sand. Two typical length to diameter ratios (L/D) are considered with the same length (L = 60 m) but different diameters (D = 4 and 6 m). It is found that the lateral behaviors of large-diameter slender pile, including its monotonic p-y response, cyclic accumulation of lateral displacement and cyclic stiffness evolution, are marginally different from those of small-diameter slender piles, but significantly deviate from the large-diameter stubby piles. This may suggest the longstanding argument of ‘diameter effect’ is relatively minor, while the lateral behavior of monopile in sand is more significantly governed by the relative pile-soil stiffness. The API (2011) non-conservatively predicts both stiffness and capacity of the large-diameter slender piles, leading to development of a new p-y formulation. These centrifuge testing results form a unique database to support development of new design methods for large-diameter slender piles, and to verify advanced numerical analyses involving cyclic models.

Estimation of the response of piled raft using nonlinear soil and interface model

ABSTRACT In this research paper, the complex interaction mechanism between different components of CPRF was simulated through 3D finite element analyses using the nonlinear interface and soil model for three case histories. The interface behaviour between concrete and soil was accounted using combined adhesion and friction model. The nonlinear soil behaviour was included using cap plasticity model, which has stress-dependant shear and compression yield surface, and captures the effect of stress history and stress path. The computed response parameters for the three case histories resulted in reasonably close agreement with the field measurements and led to significant improvement in the estimation of the load sharing of piles. The comparison of the results with the different methods showed that the stiffer interface results in a higher pile-raft coefficient and lesser settlement. The pile and soil stiffness found to vary with their position below the raft due to the different interactions.

Determination of the Pile Stiffness Matrix Based on the Pile Load Test Results and the Effect of Pile Interaction

Determination of the Pile Stiffness Matrix Based on the Pile Load Test Results and the Effect of Pile Interaction

Shaking table testing of two single piles of different stiffnesses subjected to liquefaction-induced lateral spreading

Lateral spreading is the main cause of pile foundation damage in liquefaction-prone areas during earthquakes. A soil profile in which a non-liquefied soil is on top of a liquefied soil is a critical design scenario. To investigate the influence of lateral spreading on pile responses in this type of soil profile, a shaking table test was performed on two single piles in the ground with a 2° slope. Considering different pile stiffnesses, an aluminum pile (Al pile) and a polypropylene pile (PP pile) were tested. The piles were embedded in multilayered soil comprising a clay layer sandwiched between dry sand above and saturated sand below it. The two piles had considerably different displacement and moment responses to an input motion based on a 1999 Taiwan Chi-Chi earthquake record. The experimental lateral spreading soil displacement profile approximated the cosine profile proposed by Tokimatsu and Asaka. Compared with the upper non-liquefied soil, the magnitude of the lateral spreading pressure of the liquefied soil was small. The experimental lateral spreading pressure from the non-liquefied soil layer was approximately 2.1 and 4.5 times Rankine's passive earth pressure for the PP and Al piles, respectively. The difference between the derived p-y curves of the Al and PP piles for the non-liquefied soil layer may have been due to the contribution of downhill soil reactions. To reflect the influence of pile stiffness, both the downhill and uphill p-y curves of the non-liquefied crust layer should be considered in lateral spreading analysis.

Calibration and parametric investigation of integral abutment bridges

Integral abutment bridges (IABs) are a special type of bridges that are built free of joints on the superstructure to overcome the undesirable consequences associated with conventional jointed bridges. Despite of the proven advantages of IABs, no consensus exists among bridge engineers about design guidelines. This paper presents a parametric study validated to a field monitored concrete IAB using a three-dimensional finite-element model to study the parameters that affects the bridge response. Bridge length, pile size and orientation, and soil type were included in the study. Bridge components were simulated using 3D solid elements for best reflection of the real behavior of the IAB. Nonlinear p-y method was employed to model soil-pile and soil-abutment interactions. Several shrinkage models, earth pressure theories and temperature distribution across the bridge superstructure were considered in simulating the field response of the IAB. The outcomes of the calibration process were utilized in building sound models for the parametric study. The soil stiffness around the pile was found to has more impact than the pile orientation on the pile displacement. Pile stresses were found to be proportional to the soil stiffness and inversely proportional to the pile stiffness. Moreover, the maximum stresses occurred within the middle segment of the pile rather than the pile-abutment interface due to apparent abutment rotation. The study promotes understanding of important facts which could assist in a better IAB design.

Capacity degradation method for piles under cyclic axial loads

Piles used for jacket type foundation of offshore wind turbine are subjected to highly cyclic tension and compressive loading. The pile capacity under cyclic tension loading decreases with increased number of loading cycles due to reduction of the pile shaft resistance. A numerical simulation scheme is presented, which allows the calculation of the pile capacity degradation (CDM) due to cyclic loading for driven steel piles. The volume compaction of soil near the pile surface during the cyclic loading is determined from the cyclic simple shear test results and then applied to the pile-soil system.From the limited number of tests available, interaction diagrams have been developed, which give the number of load cycles leading to failure dependent on the mean load and the amplitude of the cyclic load portion, which are both related to the static pile capacity. However, such diagrams cannot account for different soil conditions or pile geometry and pile stiffness. The calculation results for different piles in sandy soil under cyclic axial loading are presented and compared with existing interaction diagrams. Finally, recommendations regarding further investigations and improvements of the method are given.