Pile Modulus Research Articles

Stochastic seismic performance of slopes reinforced by a combination of piles and anchor cables using the probability density evolution method

ABSTRACT A combination of piles and anchor cables effectively enhances the seismic stability of slopes. However, due to the uncertainty of earthquake and soil properties, the stochastic response of slopes reinforced with piles and anchor cables (SRPC) remains unclear. This study presents a framework for the stochastic analysis of the SRPC using the probability density evolution method. The soil deformation, natural frequency of the slope, and the load sharing ratios of piles and anchor cables were investigated. Additional analysis was also conducted to evaluate the effects of the time-history characteristics and randomness of earthquakes, and pile modulus on the stochastic response of the SRPC. The results indicate that combining piles and anchor cables significantly reduced the probability of large soil deformation and increased the natural frequency of slopes compared to that reinforced with either piles or cables. However, the soil displacement increased considerably as the dominant frequency of earthquakes approached the natural frequency of the SRPC. Therefore, the variability in frequency spectra should not be neglected when considering the randomness of earthquakes. Furthermore, the load sharing ratio of piles increased dynamically and was higher than that of cables. A higher pile modulus contributed to the enhanced effectiveness of piles in sustaining earthquake loads.

Mechanical mechanism of soft soil foundation improved by geosynthetic-reinforced pile-supported technology based on field experiment

Geosynthetic-reinforced pile-supported (GRPS) technology is an effective method for improving soft soil foundations. Conducting field tests is crucial for accurately assessing the mechanical behavior of GRPS technology. Based on the fourth expansion project at Pudong Airport, field tests were conducted to investigate the effects of GRPS technology on soft-foundation treatment. Specifically, the tests examined the changes in the pile and soil settlement, pore water pressure, and pile and soil stress. The results showed that the settlement of the GRPS foundation mainly occurred during the loading period, accounting for approximately 65% of the total foundation settlement. Increasing the pile modulus and reducing the pile spacing decreased the total foundation settlement. The filling load was mainly transferred to the piles through the soil arching effect, resulting in a large excess pore water pressure in the soil layer near the pile tip. In addition, when the filling height was low, the load transfer relied predominantly on the tensile membrane effect of the geogrid, which was more pronounced near the piles. However, as the filling height increased, the soil arching effect surpassed the tensile membrane effect and played a key role in load transfer.

Safety Criterion for Hollow Pipe Piles Under Blasting Vibration Based on Wave Function Expansion Method

When the drilling and blasting method is used to excavate urban subway tunnels, the blasting seismic waves will inevitably produce vibration effects on the pile foundations under the surface buildings, which will seriously threaten the safety of surrounding buildings and the environment. Based on the transmission and reflection laws of stress waves at the interface between soil medium and pile medium and the displacement–stress continuous assumption, the wave function expansion method is used to analyze the whole process mechanism of vibration effect of hollow pipe piles under the action of incident [Formula: see text] waves. In addition, the theoretical model of safety criterion for hollow pipe piles under blasting vibration is proposed and the reliability of the model is verified. Furthermore, the impacts of the elastic modulus, density, and pile section parameters of soil and piles on the safety criterion for the blasting vibration effect of hollow pipe piles are analyzed. The results show that as the elastic modulus and density of the soil increase, the critical peak particle velocity (PPV) curves of hollow pipe piles move to the high-frequency and low-frequency bands, respectively, resulting in a decrease in the overall safety of piles. This indicates that hollow pipe piles should not be buried in soil layers with high elastic modulus and density. It is also shown that the larger the hollow area of hollow pipe piles, the lower their safety. Compared to solid circular piles, hollow pipe piles have a higher overall seismic safety reserve. The study results have guidance and reference value for effectively evaluating and controlling the harm of blasting vibration effects of hollow pipe piles.

Bearing Capacity and Deformation of the Tandem Compound Piles Improved Foundation: A Parametric Study.

The tandem compound piles are a combination of a granular column in the deep section and a concrete pile in the shallow section. This method effectively utilizes the consolidation and densification effects of the granular column, as well as the cementation strength of the concrete material. The granular column acts as a consolidation path, aiding in the densification of the surrounding soil. On the other hand, the concrete pile prevents the bulging deformation that commonly happens in granular columns during field construction. To study the bearing capacity and deformation of the improved foundation with tandem compound piles, a coupled continuum-discrete numerical model was developed in this study. The accuracy of the model was confirmed by comparing its results with experimental measurements. Additionally, a parametric study was conducted, considering three influential factors: (1) cushion thickness and modulus, (2) length, modulus, diameter, and spacing of the tandem compound pile, and (3) soil modulus. The results indicated that reducing the cushion thickness and increasing the cushion modulus allowed the pile to bear more loads. Moreover, increasing the length and modulus of the deep section of the pile reduced deformation and improved the bearing capacity. The pile modulus, however, had a limited effect on enhancing the bearing capacity. It is important to maintain a critical pile spacing of at least twice the pile diameter. Finally, a high modulus of the underlying stratum led to higher vertical and radial stresses in the pile.

Buckling failure mechanism and critical buckling load prediction method of super-long piles in soft-clay ground in deep water

Buckling may be a possible failure mode of super-long piles in soft-clay ground in deep water as concerned by several researchers. Although there are many studies on the failure mode of super-long piles in sands or silts deposits, few studies have been carried out thoroughly on mechanical mechanism of buckling instability in soft-clay ground in deep water and the corresponding calculation method. In this paper, first, the Riks Arc-Length method in ABAQUS was evaluated and verified using the FEM simulation and the analytical results from Bhattacharya. It is observed that buckling failure is indeed one of failure modes of super-long piles in soft-clay ground. And then, the buckling capacities of super-long piles were assessed due to various influential parameters. The results show that the critical buckling load of super-long piles increases with the increase of elastic modulus and embedding rates of piles, and the increase of elastic modulus and cohesion of soil, while decreases with the increase of slenderness ratios of piles and horizontal loads. Finally, a prediction method of the critical buckling load for super-long piles was presented based on the above sensitivity analysis for influential parameters and the Euler buckling formula, and the criterion for buckling instability for super-long piles was proposed as well.

Study on the Lateral Dynamic Impedance of Pile Groups in Transversely Isotropic Soil Using Novak’s Plane Model

In order to consider the effect of anisotropy of soil around the pile on the lateral vibration of pile groups, the soil around the pile is regarded as a transversely isotropic medium, and a lateral dynamic interaction model of pile-pile in transversely isotropic soil is established. According to Novak’s plane assumption and wave propagation theory, the lateral vibration of transversely isotropic soil layer is solved by introducing potential function and using mathematical and physical means, and the attenuation function of lateral displacement of free field is given. The Dobry and Dazetas simplified solution of attenuation function is different from that of solution of plane model. The pile-pile horizontal dynamic interaction factor in transversely isotropic soil is obtained by using the initial parameter method and Krylov function. The horizontal dynamic impedance of pile groups is obtained by using the pile-pile superposition principle. The change rule of the lateral displacement attenuation function of transversely isotropic soil with frequency is related to the direction and frequency. The ratio G h v of the shear modulus in the lateral plane to the shear modulus in the vertical plane and the pile spacing S / d have a great impact on the lateral vibration of pile groups, and when the pile spacing is large, the curves of attenuation function varying with frequency fluctuate greatly. The ratio of elastic modulus of pile to vertical plane shear modulus of soil E p / G v has an effect on the lateral stiffness of pile groups, which is related to frequency, while the effect on dynamic damping is not affected by frequency. The difference of mechanical properties on different surfaces of soil around the pile has a great influence on the lateral vibration of pile groups in transversely isotropic soil, and the influence of the anisotropy on the attenuation function of the lateral displacement and the dynamic impedance cannot be ignored.

Dynamic responses of the sheet–pile groin under tidal bore considering the soil–structure–water interaction

ABSTRACT A sheet–pile groin composed of two rows of piles connected by sheets has been applied to resist tidal bores. This study develops an analytical framework to thoroughly investigate the dynamic responses of the sheet–pile groins under tidal bores. The piles are modeled as an Euler–Bernoulli (EB) beam, while the sheet is simulated as a Rayleigh–Love rod and an EB beam considering the vertical flexural inertia effect. The hydrodynamic pressure is calculated by using radiation wave theory. The saturated soil around the piles is described with dynamic Biot’s poroelastic theory, while the additional mass model adopts the interaction between the piles. The applicability and correctness of the formulas are verified by comparing them with numerical simulation results. It investigates the influence of water depth, sheet length, pile radius and the ratio of the soil–pile modulus on the dynamic impedance of the sheet–pile groin. Suggestions based on this study are given to guide sheet–pile groin design to avoid the resonance frequency and improve the impedance in practice engineering.

Modulus of Laterally Loaded Pile in Cohesionless Slope Crest with Varying Condition

Soil - structure interaction behaviour of pile foundation is complex for heavier structures which suffer large lateral load due to wind, wave action etc., in addition to the large vertical and oblique load. The parameters involved in determining the lateral capacity of the foundation are its structural geometry, soil properties and ground condition. The behaviour is different for horizontal ground compared to the sloping ground; it is even different under loading and unloading conditions. In this study, the modulus of single pile is studied under various lengths, diameters, slope angles and loading directions. An equation is generated is developed to obtain the modulus with varying length and diameter.

Behavior of isolated floating pile adjacent to deep excavation reinforced by dual-row batter pile wall

The construction of modern city consists of many underground facilities, and one major concern is how to construct them safely and efficiently. Thus, the excavation-induced pile response needs to be evaluated. Dual-row batter pile wall (DRBPW) exhibits better performance than traditional dual-row vertical pile wall (DRVPW) in foundation pit engineering. However, the study of single pile subjected to excavation-induced soil movement behind DRVPW is rather limited, needless to say that of the DRBPW. An explicit finite difference method (FDM) was utilized to obtain the responses of isolated floating single pile (IFSP) near deep excavations braced by DRBPW. The responses of IFSP in the vicinity of foundation pit reinforced by DRBPW were compared to that of the DRVPW. The pile length, distance of pile from wall, excavation depth, working load, and Young’s modulus of pile were considered in the parametric study. The conclusions were as follows: (1) The DRBPW can minimize the influence on the existing pile; thus, the induced lateral displacement and bending moment of pile retained by DRBPW are smaller than that of DRVPW. (2) The excavation depth, pile location, and pile length have significant influence on the responses of IFSP adjacent excavation, while the working load and Young’s modulus of pile have diminutive influence. (3) The influence zone induced by excavation can be divided into two areas. The primary influence zone is the severely affected area where the induced deformation and bending moment are remarkable. The secondary influence zone is the moderately affected area where the induced deformation and bending moment are mild. The primary influence zone is within twice of the excavation depth. The secondary influence zone is 2.0–3.0 times that of the excavation depth. (4) The pile toe of IFSP has considerable lateral displacement during excavation, and attentions should be paid to the whole pile shaft during construction.

3D Numerical Modeling of Pile embankment performance on Soft Soil

Embankments are often required in many civil engineering construction projects involving infrastructure development to elevate the ground level. Due to the limitation of land availability for infrastructure projects in many countries, a large number of projects are now being carried out on soft ground. However, embankment construction over soft ground is a challenging task due to several undesirable characteristics associated with soft soils such as local instability, inadequate bearing capacity and large settlements, which can occur over a long period of time. These problems can generally result in expensive remedial measures and long construction delays. The conventional soft ground improvement methods based on consolidation such as vertical drains and preloading are not suitable when projects have to be completed within a short period of time or the ground improvement has to be carried out in contaminated ground. In such situations, reinforced pile-supported embankments are increasingly used as an alternative construction method due to the shorter construction time required compared to consolidation based methods and due to the higher reliability of the method when the subsoil properties cannot be relied upon. . This paper presents a comprehensive numerical study carried out using the finite element method in order to investigate the performance of reinforced pile supported embankment. A detailed parametric study is presented inthree-dimensional conditions incorporating the full geometry of embankment system. The influence of pile embedded length, pile diameter, elastic modulus of piles, height of the embankment, construction rate of the embankment were investigated on the performance of the selected embankment.

Transient thermal response of a thermally activated pile during a long-term maintained load test at Lambeth College, London

The energy pile test at Lambeth College, London was first reported just over 10 years ago; however, the original appraisal of the test only looked at the thermal response at the end of extended cooling and heating stages, and did not examine the transient response within these stages or in the daily cyclic thermal loading stage that followed. This paper revisits the earlier results, allowing for concrete creep under sustained load and using a revised strain-dependent pile modulus. The strong influence of the latter and the possible importance of stiffness changes during load reversal is highlighted. Detailed evaluation of the long-term transient results suggests that within a given thermal loading interval the thermal effects are similar, but there is some further discrepancy in the results, possibly due to an underestimation of the concrete creep. This re-evaluation has mitigated pile head displacement and increased thermal stress in the cooling phase, with the reverse occurring in the heating phase, and appears to be in better agreement with back-analysis reported by others. The transient response within the thermal loading stages illustrates that the development of the thermal stress–displacement response is related to the time for heat to diffuse through the pile body – around 3 days in this case.

Simulation of pile cap contribution to the lateral pile performance due to adjacent excavation

Laboratory and field test data on the lateral pile response with caps due to adjacent excavation are rather limited. The current practice for design of capped piles is to consider the cap resistance and the pile capacity independent of each other. This paper presents some results from three-dimensional finite-difference analyses that couple the constrain effect of pile cap on the lateral pile performance adjacent to an excavation. The analyses were performed in saturated homogeneous clays, and 38 cases of various pile head conditions restrained by caps including embedded depths of the pile into the cap, relative pile cap–pile modulus and pile cap–pile interface stiffness were carried out. The results have shown that the pile–pile cap connections can significantly affect the distribution of lateral pile deflections and bending moments and change the lateral pile performance, especially with a deep-buried and completely fixed cap. To combine the effects of the pile head embedded depths and the cap material properties, a convenient design method based on statistical analysis for estimating the pile–pile cap connections was presented. The proposed constraint coefficient method can be used to assess the lateral performance of the capped pile and simplify the design procedure of the pile cap due to excavations.

Study on Long‐Term Performance of Geogrid‐Reinforced and Pile‐Supported Embankment at Bridge Approach

Bridges have been widely used in highway and railway engineering, especially in mountain areas. The differential settlement between bridge abutment and approach embankment is one of the most challenging problems, and it will result in “bumps” to affect the driving safety and comfortableness at the end of a bridge. The geogrid‐reinforced and pile‐supported embankment (GRPS embankment) is proposed to mitigate the differential settlement at the bridge approach. In this paper, the model tests and numerical studies are carried out to study the long‐term performance of the GRPS embankment considering the consolidation of subsoil. Firstly, a series of model tests are conducted to evaluate the long‐term performance of the GRPS embankment using a specially designed model box. Then, the numerical model is constructed using the finite element software MIDAS, and the numerical model is verified from the model test results. Finally, a parametric study is conducted to investigate the influences of pile net spacing, pile modulus, and filling modulus.

Study on Bearing Capacity of Tank Foundation with Alternatively Arranged Vortex-Compression Nodular Piles

Types of tapered piles are widely applied in tank foundation consolidation, but their inherent deficiencies in design and construction limit their further promotion. Vortex compression pile is a novel nodular pile. Compared with the traditional equal-section pile, vortex compression nodular pile is featured by stronger bearing capacity and slighter settlement. In this paper, the model test results showed that vortex compression nodular pile can greatly improve the bearing capacity and reduce the settlement. Through the finite element software ABAQUS analysis the bearing characteristics of equal-section pile foundation and vortex-compression nodular pile foundation were compared. The three-dimensional solid model was established by ABAQUS finite element software. The impact of cushion modulus, cushion thickness, vertical load, pile modulus, soil modulus around the pile on the bearing capacity of the vortex-compression nodular pile foundation were studied.

Study on Vertical Vibration of Partially Exposed Friction Pipe Pile Groups Based on Fictitious Soil Pipe Pile Model

Regarding soil below the pipe pile as fictitious soil pipe pile, the vertical dynamic model of partially exposed friction pipe pile is established. Winkler spring-damper model is used to simulate the vertical dynamic interaction between soil around the pile and pipe pile, and between pile core soil and pipe pile by ignoring the radial displacement and circumferential displacement of soil. Considering the displacement boundary conditions of the soil around pile and pile core soil, the effects of the soil around pile and pile core soil on the pipe pile are obtained, and the complex stiffness of vertical vibration of a partially exposed friction pipe pile is obtained by using the initial parameter method and the transfer matrix method. The vertical dynamic interaction factor of partially exposed friction pipe pile-pipe pile is obtained by considering the dynamic interaction between pipe pile and pipe pile. Based on the principle of pile groups superposition and the vertical dynamic interaction factor of pipe pipe-pipe pile, the vertical vibration of partially exposed friction pipe pile groups is studied, and the vertical dynamic impedance of pipe pile groups is also obtained, and the influences of relevant parameters on the vertical dynamic impedance of partially exposed friction pipe pile groups are investigated by numerical examples of 3 × 3 pipe pile groups. The results show that the dynamic stiffness and damping of end-bearing friction pipe pile groups are larger than friction pipe pile groups, and the change of peak values of curves varying with frequency are gentler. The restraint effect of bedrock under pipe pile can increase the vertical dynamic impedance of pipe pile groups. Increasing the length of pipe pile is beneficial to increase the vertical dynamic impedance of pipe pile groups. The larger the pipe pile spacing, the sharper the peak values of curves of the dynamic stiffness and damping curves of pipe pile groups varying with frequency. The influence of pipe pile geometry on vertical vibration of pipe pile groups is greater than that of physical properties such as elastic modulus of pipe pile and shear modulus of soil.

Analysis of ground vibrations induced by high-speed train moving on pile-supported subgrade using three-dimensional FEM

The pile-supported subgrade has been widely used in high-speed railway construction in China. To investigate the ground vibrations of such composite foundation subjected to moving loads induced by high-speed trains (HSTs), three-dimensional (3D) finite element method (FEM) models involving the pile, pile cap and cushion are established. Validation of the proposed model is conducted through comparison of model predictions with the field measurements. On this basis, ground vibrations generated by HSTs under different train speeds as well as the ground vibration attenuation with the distance away from the track centerline are investigated. In addition, the effects of piles and pile elastic modulus on ground vibrations are well studied. Results show that the pile-reinforcement of the subgrade could significantly contribute to the reduction of ground vibrations. In particular, the increase of elastic modulus of pile could lead to consistent reduction of ground vibrations. However, when the pile elastic modulus is beyond 10 GPa, this benefit of pile-reinforcement on vibration isolation can hardly be increased further.

Effects of soil arching on behavior of pile-supported railway embankment: 2D FEM approach

Abstract The construction of railway embankment on soft soil is a challenging task for practitioners. In the past, several approaches have been employed in practice to overcome this problem. Pile foundation is considered one of the reliable solutions for soft ground. In a pile-supported railway embankment, soil arching plays a vital role in the efficient load transfer to the piles. In this study, the soil arching phenomenon in a granular embankment subjected to train induced loading is demonstrated based on the two-dimensional (2D) finite element modeling approach. A 2D plane strain idealization is used to convert a real three-dimensional (3D) case into 2D. The effects of the piled railway embankment properties on soil arching are investigated. It is found that pile modulus, embankment modulus and friction angle affect the arching mechanism significantly. Pile spacing (s) variation affects soil arching (i.e., the arching zone can be increased by reducing s). In addition, the height and shape of arching are studied. A comparison with the available analytical design methods for embankments is presented which indicates inconsistencies in the previously published results.

The role of concrete creep under sustained loading, during thermo-mechanical testing of energy piles

The energy pile test at Lambeth College London was first reported some 10 years ago, and since the results were published, some potential anomalies in the results have been identified. This article revisits the results of this test using a strain dependent pile modulus, accounting for residual strain from unload/reload loops and allowing for concrete creep under sustained load. The result of this re-evaluation has been to substantially modify the interpreted pile response, especially near the pile head, which leads to a mitigation of the maximum pile head displacements in the cooling phase, and the maximum thermo/mechanical stresses in the heating phase. Two other case studies have been examined to illustrate that concrete creep may be a significant factor in the responses of each, and it is concluded that existing studies should be re-examined and future testing should account for concrete creep. It is highlighted however that while the quantitative interpretation of the test has changed, the underlying mechanisms of behaviour remain consistent with those described in the literature.

Dragload of pile groups in consolidating non-Darcian clays

In the present study, the behaviour of pile groups with flexible cap in consolidating non-Darcian soil is investigated in terms of dragloads and downdrag. The effective stresses and the settlements are computed at different depths of the soil layers using a non-linear, one-dimensional consolidation equation for variable permeability and the non-Darcian condition. The relationship between displacements and shear stresses at the pile–soil interface and at the pile tip are modelled using a hyperbolic function. The proposed model is validated with the reported experimental results. The effects of pile spacing, slenderness ratio, soil modulus, pile modulus and the effects of non-Darcian parameters (α and n) on the developed dragload and downdrag have been studied for line pile groups (3 × 1), square pile groups (2 × 2, 3 × 3 and 5 × 5) and rectangular pile groups (3 × 2). It is observed that the central pile of a 5 × 5 pile group mobilises only about 30–45% of dragload as compared to the single piles during 1 year to 10 years of consolidation. In a 2 × 2 pile group, only 20–30% of ultimate pile settlement is attained after 5 years of consolidation owing to the non-Darcian condition, in comparison to 90% of ultimate settlement for the Darcian flow condition.

Optimization analysis of modern tram embedded track composite foundation

In order to analyze the key parameters of tram embedded track composite foundation and get the optimal combination of parameters, the finite element method is applied to establish the calculation model of embedded track composite foundation. Based on the existing research, the influence of five key factors, such as the thickness of track plate, the thickness of supporting layer, the elastic modulus of pile, the diameter of pile and the longitudinal spacing of pile, on the stress and deformation of embedded track composite foundation is studied by orthogonal test. The results of the calculation are analyzed with the difference analysis and variance analysis, and the key factors and the optimal combination of parameters are obtained. The results show that the orthogonal test method can greatly reduce the number of tests on the basis of ensuring the correctness of the analysis results. The elastic modulus of pile has the greatest influence on the vertical displacement of rail. The thickness of supporting layer has the greatest influence on the longitudinal bending moment of track plate, and the pile diameter has a great influence on the vertical displacement of rail. The longitudinal spacing of pile has a great influence on the vertical displacement of rail, longitudinal bending moment of track plate and longitudinal tensile stress of supporting layer. Therefore, when determining the longitudinal spacing between piles, the service performance of track structure and the cost of composite foundation should be considered comprehensively. The design scheme of optimal tram embedded track composite foundation is the thickness of track plate 0.20 m, the thickness of supporting layer 0.26 m, the elastic modulus of pile 280 MPa, the diameter of pile 0.75 m and the longitudinal spacing of pile 1.40 m. The results of this study have reference value for the design of tram embedded track composite foundation.