Behavior Of Piles Research Articles

Shaft Friction Characteristics of Two FRP Seawater Sea–Sand Concrete Piles in a Rock Socket with or without Debris

Abstract The existence of debris at the bottom of a rock socket significantly influences the mechanical behavior of a rock-socketed pile. To investigate the effects of debris on shaft friction and ...

Design and first operation of the MACARON irradiation experiment of Sodium Fast reactor absorber pins in the BOR-60 reactor

The development of the next generation of Sodium-cooled Fast Reactors (SFRs) needs to integrate innovative options regarding the core design in order to comply with the objectives of the 4th generation reactors in terms of safety, cost and performance. In this framework, the aim to design fast core with economy improvements leads to limit the number of control and shutdown systems and to extend their lifetime. These objectives require choosing absorber material with maximal efficiency in terms of neutronic absorption.The French concept of absorber pin is based on the use of boron carbide (B4C) pellets with 10B various enrichments and the absorber element consists of a vented non-leaktight pin with a permanent sodium bond between the pellet column and the stainless steel clad.In order to test an innovative concept of absorber pin and with the aim to improve in one hand, the in pile behavior understanding and in the other hand, the absorber rod modelling codes, an experimental program named MACARON is undergone. This program consists in an irradiation test in the BOR-60 reactor following by a complete NDE and PIE program. Two short absorber pins are irradiated currently. This program is performed by both CEA and RIAR teams.A brief description of the experiment is first provided, in terms of objectives. The main characteristics of absorber pin with the main design criteria are detailed. The manufacturing steps and the characterization of the experimental absorber pins are given with as manufactured results.The design studies of the Irradiation Rig and the neutronic and thermal hydraulic calculations are described in details. The irradiation test has begun in September 2018 and the first experimental results are provided. The huge program of Non-Destructive and Destructive Examinations is detailed with experimental objectives and methods that will be used.

Investigation of Pile Behavior Toward Abutment Construction using PLAXIS 3D: Case Study on Lembak Bridge

Soil as a subgrade foundation under embankment construction often creates problems in terms of stability and settlement. Therefore, it needs improvement by using preloading embankment. This article presents the investigation of pile behavior towards two scenarios of abutment construction using Plaxis 3D, a three- dimensional finite element program. The use of two scenarios of analysis was Method A. The abutment construction phase conduct without using a preloading embankment, and Method B, where a preloading embankment constructs before the abutment construction. The case study location at the Lembak bridge. Compare the analysis results with the measured data. Results showed that Method A and Method B's pile deflection yielded four times and one point six times larger than the measure data, respectively. Hence, it indicates that Method B recommends for future construction of bridge abutment.

Behavior of Defective Cast in Place Piles

This paper deals with testing defected model piles in the soil in order to study their behavior. In this respect, the results of model pile tests are discussed either geotechnically or structurally according to the type of failure.
 
 Two parameters were studied in order to evaluate the general behavior of defective piles. These parameters include the defect location and the defect type for floating and end bearing pile. The results of the experimental work indicated that the critical case for floating pile is seen to be when the defect of (5%) at the first third of the pile length at which the decrease in the bearing capacity is about (21%), while the decrease in the bearing capacity is found to be (14%) and (10%), when the defect is at the middle and the lower third of the pile length, respectively. The decrease in the bearing capacity for floating pile is found to be (31%) and (21%) for void and neck defect, respectively, while the decrease in the bearing capacity for end bearing pile is found to be (43%) and (52%) for void and neck defect, respectively.

Physical Model Test and Theoretical Study on the Bearing Behavior of Pile in Expansive Soil Subjected to Water Infiltration

Abstract A loading test device with infiltration function is developed to conduct model tests on the bearing behavior of single piles in expansive soil. The infiltration observation test and vertic...

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.

Influence of Stratified Soil System on Behavior of Laterally Loaded Pile Groups: An Experimental Study

Laterally loaded piles are most commonly used in foundations of structures subjected to wave action, winds, earthquakes and traffic loading. More complexity is involved in analyzing the pile group response under the action of lateral loads. Soil–pile interaction significantly influences the behavior of pile groups under lateral loading. The current study aims to understand the behavior of individual pile and pile groups under lateral loads in uniform sand (relative density 80%) and stratified soil (sand overlain by clay) by conducting laboratory model tests. Test tank of length 1.52 m, width 0.76 m, height 1.2 m and model aluminum test piles of 16 mm diameter (D) and aspect ratios 12, 25 and 40 were used for the tests. The response of individual pile and 2 × 2 pile group was evaluated in terms of deflection at pile head for varying aspect ratio and pile spacing of 3D, 5D and 7D for the case of pile groups. The lateral load taken by the single pile for a deflection of 0.2D in the stratified soil was increased by 200% compared to that of the pile embedded in the uniform sand. It is noted that at all stages of the loading, the pile head deflection of the single pile and pile group was reduced for the stratified soil when compared to the uniform sand bed. However, the efficiency of the pile groups embedded in the stratified soil medium was observed to be less than that of the pile groups embedded in the uniform sand.

Numerical study of single helical piles and helical pile groups under compressive loading in cohesive and cohesionless soils

In recent years, the use of helical piles as a deep foundation option for structures has increased dramatically because they offer definite advantages over other solutions. The present study undertook a comprehensive investigation of the axial compressive behavior of helical piles in both sandy and clayey types of soil using finite element (FE) modeling. Since the helices of helical piles are more likely to disturb the soil adjacent to the pile, first some approaches are proposed to consider the effect of soil disturbance during a helical pile installation in numerical models. The numerical models have been validated and calibrated through full-scale compressive loading results using the ABAQUS software. The validated numerical models were used to investigate the load transfer mechanism of a typical helical pile in different types of sandy and clayey soil, and the numerically obtained ultimate bearing capacities were compared with the theoretical ones. Based on the comparison, it was found that the theoretical procedure overpredicts the ultimate capacity of helical piles in medium and dense sand. Additionally, different geometrical aspects of a typical helical pile were investigated using FE modeling in order to employ perfect geometry for studying the compressive behavior of a helical pile group with a square grid arrangement. The results revealed that the shape of the block failure mechanism in clayey soil differs from that in sandy soil. The acquired shapes are used to suggest a theoretical method for calculating the ultimate bearing capacity of a helical pile group based on the block failure mechanism.

Influence of Geometry and Separation Walls on The Behaviours of Pull-out Pipe Piles Embedded in Sandy Soil

Predicting of piles capacity and their behavior is always an important and serious problem for a safe geotechnical engineering design. In the present study, experimental model tests have been conducted on a single steel pipe piles driven in sandy soil and subjected to pull-out force. The experimental tests were conducted on vertical open-ended piles with circular and square cross-sectional area and three various diameters 3 cm, 4 cm and 5 cm in a steel soil box have been used. The tested pile’s model has embedment with three penetration ratios (PR=L/D) of 10, 15 and 20. All tests were done in medium density soil (Dr = 50%) with open ended pipe pile to study the effect of pile geometry on pile behavior, and three other tests were conducted on the 5cm diameter and 10 penetration ratio in medium soil density to study the importance of addition of separating wall. The study discovered that the capacity of single piles with circle cross-section area under pull-out force increasing by 211% and 458% with the increasing of pile diameter (width) from 3cm to 4cm and 5cm respectively, and increasing by 210%, 448% and by 112%, 288%. Also, by 79% and 211% with increasing penetrating ratio (PR) from 10 to 15 and 20 for diameters 3cm, 4cm and 5cm respectively, with respect to reference pile. And the same behavior for square cross-section pipe pile, when the pull-out capacity increasing with the increase of pile width and penetration ratio due to the increasing in the friction area. Besides that, It was also found that the separation walls increased the coefficient of lateral pressure in addition to the friction area. At the same time, there are an optimum number of separation walls that can be used to increase the pile pull-out capacity and that when using three separation walls.

The P-y Response of Laterally Loaded Flexible Piles in Residual Soil

This paper describes the main features related to lateral displacements with depth after successive lateral loading–unloading cycles applied to the top of reinforced-concrete flexible bored piles embedded in naturally bonded residual soil. The bored piles under study have a cylindrical shape, with 0.40-m in diameter and 8.0-m in length. Both bored piles types (P1 and P2) include an embedded steel pipe section in their center as longitudinal steel reinforcements: pile type P1 has another 16 steel rods as steel reinforcement to concrete while pile type P2 has no further steel reinforcement. Pile type P1 has three times as much stiffness (EI) and four and a half times the plastic moment (My) than pile type P2. A similar load–displacement performance was observed at initial loads as for small displacements of both piles. At this initial loading stage, the response of the reinforced concrete piles is a function of the soil characteristics and of a linear elastic pile deformation. During this stage, piles can even be understood as probes for evaluating soil reactions. For larger horizontal displacements, after the concrete section starts undergoing large deformations, approaching the ultimate bending moment, pile behavior and consequently the load–displacement relation starts to diverge for both piles. For pile P1 the values of relevant lateral displacements are extended to about 2.5-m in depth, while for pile P2 lateral displacements are mostly constrained to about 2.0-m in depth. Measurements of horizontal displacements of pile P1 against depth recorded with a slope indicator show that, after unloading, lateral loads at distinct stages (small and near failure loads), exhibits a much higher elastic phase of the system response. An analytical fitting model of soil reaction is proposed based on the measured displacements from slope indicator. The integration of a continuous model proposed for the soil reaction agrees fairly well with the measured displacements up to moments close to plastic limit. Results of load–displacement show that the stiffer pile (P1) was able to mobilize twice as much lateral load compared to pile P2 for a service limit displacement of about 20 mm. The paper shows results that enable the isolation of the structural variable through real scale pile load tests, thus granting understanding of its importance and enabling its quantitative visualization in examples of piles embedded in residual soil sites.

Discrete element simulation on the behavior of open-ended pipe pile under cyclic lateral loading

The offshore pile foundations are subjected to lateral cyclic loadings such as winds, waves, and currents with complex force characteristics, which can cause complex structure responses. In this paper, the discrete element method (DEM) is used to carry out a numerical study on the force characteristics of open-ended pipe piles under lateral loading. The simulation results show that the pile rotates under cyclic loading, the centre of rotation is about 85% of the buried depth of the pile, and the cumulative angle of the pile is less than 0.1°. When a periodic load is applied, the soil around the pile is disturbed, resulting in plastic displacement, and the soil affected area around the pile forms a “butterfly shape”. The displacement in the “active zone” is larger than that in the “passive zone”. As the cycle time increases, the horizontal stiffness gradually decreases in the first 10 cycles, and the attenuation amplitude reaches more than 29% after 100 cycles. The reduction of the internal and external frictional resistance of the pile mainly occurred in the first 10 cycles, and the reduction was less than 15%. It can be seen from the static p-y curve of the pile foundation after cyclic loading that the larger the load amplitude, the greater the reduction in the bearing capacity of the pile foundation under cyclic loading. In addition, the reduction in the bearing capacity of the pile foundation under one-way loading is larger than that under two-way loading.

Inelastic lateral and seismic behaviour of concrete-filled steel tubular pile foundations

Undertaken with industry, this paper analyses concrete-filled steel tube (CFTs) pile members in deep foundation systems under cyclic and seismic loads considering inelasticity for both pile and soil. Real seismic events have pointed out that piles may fail by forming multiple plastic hinges at various location or global buckling instability. This study confirms that CFT piles efficiently reduce damage in pile-heads and over the pile length, in depths that is difficult to access and repair the damage. The paper performs a set of analyses that enables understanding of the nonlinear mechanical behaviour of CFT piles and soil-structure interaction effects. The capacity margins of the novel foundation system are firstly assessed through controlled loading analyses (i.e., monotonic and cyclic loading histories), and then investigated further by a two-level seismic-intensity analysis. CFT pile damage patterns, displacement profiles and residual displacement are discussed and compared with those of corresponding concrete piles. Moreover, comparisons with four test campaigns taken from the literature confirm the correctness of the adopted nonlinear models for soil-pile interaction and soil inelasticity. Although its simplicity, the developed p-y modeling can successfully account for soil degradation effects making possible the simulation of the rather demanding, but advanced “s” shape of soil's cyclic behaviour, allowing for a reasonable comparison between composite and concrete piles. While the damage areas of both CFT and RC piles are mainly developed in pile heads and stiffness-discontinuous soil layers, CFT piles exhibit a lower damage than that of the RC piles nearly by 40% on average.

Thermomechanical behaviour of an energy pile–raft foundation under intermittent cooling operation

This paper presents two in situ experimental investigations of the influence of intermittent and continuous cooling operation on thermal and mechanical responses of a foundation. The experiment was conducted with 16 h of cooling operation and 8 h of rest (C-16 mode) for 46 days and with 24 h of cooling operation (C-24 mode) for 32 days. A lower number of daily operating hours promoted natural ground thermal recovery and led to higher heat exchange rates with lower thermal loads on the foundation. The constant heat exchange rate in C-16 was approximately 115 W/m, which was 53.3% higher than the constant heat exchange rate at the same time in C-24. The pile temperatures at all depths in C-16 were decreased by 29.0–36.8% compared to those in C-24. Thermally induced stresses of the pile and raft in C-16 were 25.8–35.7% and 85.9% lower than the thermally induced stresses of the pile and raft in C-24. The mechanical responses of the energy pile in C-16 were reversible. During the cyclic cooling and recovery of C-16, stable changes in axial strain and stress with pile temperature were observed over further cycles, without significant variations in pile end displacement and the vertical stress at the pile toe.

Sway-Rocking Spring System Applicable to Short-Rigid Monopile Foundations

Sway-Rocking (SR) spring system is a foundation modelling method in which a 2 × 2 spring stiffness matrix represents the foundation stiffness at seabed level. Since each individual element of the spring stiffness matrix is a function of a few physical properties of the soil and pile, it is the simplest and computationally cheapest method to estimate the deformation at the seabed level and the natural frequency of an offshore wind turbine structure. Formulae currently available are only applicable to conventional long-flexible piles or perfectly rigid foundations such as footings or caissons. This study aims to extend the application of the SR spring system to a so-called short-rigid pile range, which lays between the two ranges: long-flexible and perfectly rigid. Monopiles, the most commonly selected type of offshore wind foundations, are categorized in the short-rigid pile range. By conducting three-dimensional finite element analyses, the short-rigid pile behaviour is investigated. Based on the results, a new set of formulae of the SR spring stiffness, which is applicable to a wide range (long-flexible, short-rigid and perfectly rigid) of piles, is proposed. The new formulae also improve the accuracy of frequency estimation for practical use cases.

Responses of single and group piles within MSE walls under static and cyclic lateral loads

To investigate the behavior of piles and the performance of the mechanically stabilized earth (MSE) walls under static and cyclic lateral loading, six reduced-scale model tests of single and group piles within the MSE walls were conducted inside a test box. In the single pile tests, a hollow aluminum tube as a pile was placed at a distance of 2D or 4D (D is pile diameter) behind the wall facing, while in the group pile tests, the piles were only placed at the distance of 2D with a spacing of 3.3D between the piles. The piles were subjected to static lateral loading only and cyclic lateral loading followed by static loading until failure. The test results showed that the lateral load capacity of each pile in the group pile test was approximately 60% that of the single pile, while the wall facing displacements and the geogrid strains in the group pile test were larger than those in the single pile test. The lateral pile capacity, the wall facing displacement, the strain in the geogrid, and the lateral earth pressure behind the wall facing in the static and cyclic loading tests were evaluated at the pile head displacement equal to 20%D.

The flame development process and thermal radiation of tire stacks in a large-scale experiment

In the past, most researches on tire fire are carried out small-scale fire experiments, the results are limited to reflect the details about fire development and spread characteristics in the rubber tire stacks. In this study, a large-scale experiment was carried out by two tire stacks (stacking I and stacking II) to study the burning behavior of large pile. The interior and surface thermocouples (T1–T24), exterior heat flux meters were performed, the high-definition videos were also recorded by two cameras (C1–C2). The results indicated: (1) Flames spread quickly, the melting of rubber materials in the combustion process accelerated the development of the fire. (2) The flame height variation can divide into three stages: ignition stage, development stage and stable stage. Through the analysis of three stages, we found that despite ignition durations are different, fire development after ignition of tire stacks shows similarities. (3) The highest temperature was found in the inner part of the stacks, suspected that the melting and dripping material of surface tires ignited the inner tire, or the plume attenuation effect caused heat accumulation occurred inside the stacks. (4) A thermal radiation calculation model was established to roughly estimate the heat flux and compared with measured values; the relative error is about 55.23%. Due to the parameter selection and other influence factors, the relative error is within the acceptable range.

Coupling hardening soil model and Ménard pressuremeter tests to predict pile behavior

This paper presents a simple method to apply the Ménard Pressuremeter Test (PMT) results for the calibration of the soil stiffness due to primary deviatoric loading used in the Hardening Soil (HS) Model. A hyperbolic extension is used to rebuild the PMT pressure-expansion curve at small-strain values. The method was applied to simulate a series of PMT tests using axisymmetric finite element analysis (FEA) and was compared with the conventional HS model calibration using consolidated drained triaxial tests with reasonable accordance. Finally, the method was used in axisymmetric FEA of two static load tests in instrumented piles, performed in different sites. The results indicate good agreement between predicted and measured values of pile load-settlement behavior, average shear stresses at pile shaft and pile base pressure considering usual pile working loads. For highly mobilized piles, the numerical simulations indicated that an increase in soil cohesion was able to match the predictions of pile failure, in order to consider in a simplified way the effects of soil suction and pile execution procedure, which were not simulated herein.

Effect of vertical loads on pile group response subjected to lateral cyclic loading with different configuration of piles: experimental study

Many previous studies have mainly investigated only the effect of cyclic loading on the behaviour of group pile without taking in to account the influence of axial load in the other mean (without the effect of vertical load on the behaviour on the group pile), which is represented most realistic case. In addition, due to the large number of variables in soil and piles, which make these studies not fully understood, so deep studies of the behaviour of the group pile is needed. This study aiming to knowing the effect of axial load and piles shape on the performance of piles group under cyclic loads and identifying the best configuration of piles also to study the effect of pile spacing on lateral displacement under pure and combined loading. by developing cyclic laboratory system that can test the pile of group. Aluminium pile with slenderness ratio L/D of 40 in-groups (1×2), (2×1) is used in this study. The most important results explained that the presence of vertical loads on the pile group cap according to allowable vertical load capacity and the pile shape have positive effect. Where it is reducing the lateral displacement of the head group pile a rounded of 60 %and 30% respectively.

The Effect of installation Torque on the Behavior of Helical Piles under Compression Load Tested by Centrifuge Device

In complex geotechnical problems, to perform a realistic study related to the soil-structure interaction and bearing capacity of foundations, a centrifuge modeling must be considered. New centrifuge device for installation and testing screw pile models is designed and manufactured with different velocities depending on the value of N (gravity scaling factor) and applying compression, uplift and inclined loads during rotation and their electronic control. The new installation system for helical piles was used in this device to install each pile with different torque depending on its capacity. Helical piles represent one of the deep innovative foundations as an alternative for increasing the size of the existing foundation solutions. In this study, the helical pile models are tested by centrifuge device with different parameters embedded within sand with relative density (R.D) of 75% and 55% under compression load. These parameters are spacing ratio, diameter and number of helices. The installation torque causes a soil disturbance which increases by increasing the diameter of helix and R.D of soil. The reduction percentages of the bearing capacity of the helical pile models with two helices of diameter (40 mm) embedded in sand with R.D of 75% and 55% are 17% and 9%, respectively, and when R.D of (55%) and helix diameters of 40 mm and 50 mm are 9% and 15%, respectively.

Siesmic Response of Single Pile Soil Structure Interaction Effect of Cordera bridge foundation

The response of single pile foundations to the dynamic loads is considered in this paper. The behaviour of such foundation is important specifically in case of earthquake excitation through the supporting soil medium. An axisymmetric finite element model has been implemented to simulate the behaviour of pile in relatively clayey soil deposit using Abaqus software including the soil structure interaction effect soil system. Eight node axisymmetric quadrilateral element CAX8R used to simulate the soil continuum. Contact behaviour between the single pile part and the part of soil was simulated using the ‘surface to surface’ contact method with master-slave concept. Furthermore, the pile behaviour material has been simulated with a linear elastic model while, soil material has been simulated with an elasto-plastic model “Mohr-Coulomb failure criterion”. Two different excitation have been adopted during the analysis: El-Centro and Ali-Algharbi earthquakes in order to investigate the effect of various intensities. The results of the analysis demonstrate alteration in the relative displacement and stresses along the pile with different soil layer and different stiffness with both earthquake excitations.