Normal Pile Research Articles

Semi-analytical study of defective pile-beam systems under transient excitation: Implications for low-strain testing

This paper establishes a theoretical model of defective pile-beam system. The soil around the pile is modeled as a continuous three-dimensional model. The pile is modeled as a Rayleigh-Love rod model that considers its transversal inertia effect. The defect of the pile is simulated by a pile segment with a different radius from the normal pile segment. The impedance function recursion method, along with RSPT and AIFTM, is utilized to derive the impedance of the pile top. The beam is modeled as a Timoshenko beam and the transient excitation is applied at the connection between the pile and the beam. Analytical solution for the dynamic response of the system in the frequency domain is derived, and the discrete Fourier transform is used to obtain a semi-analytical solution for the time-domain response. The velocity at the connection between the pile and beam and the pile body can be measured to assess defects. The semi-analytical solution presented in this paper was validated through comparison with FEM results. Reflection from necked segment is more pronounced at pile-beam connection than at pile body. Both velocity curves at these two points should be measured when beam cross-section height is large to determine pile integrity. The peak value and arrival time of characteristic waves are influenced by burial depth, necking section parameters, beam cross-section height, cantilever length, and soil parameters. These findings can provide guidance for the application of low strain integrity testing in pile-beam systems.

Behaviour of Extractives in Norway Spruce (Picea abies) Bark during Pile Storage.

The current practices regarding the procurement chain of forest industry sidestreams, such as conifer bark, do not always lead to optimal conditions for preserving individual chemical compounds. This study investigates the standard way of storing bark in large piles in an open area. We mainly focus on the degradation of the most essential hydrophilic and hydrophobic extractives and carbohydrates. First, two large 450 m3 piles of bark from Norway spruce (Picea abies) were formed, one of which was covered with snow. The degradation of the bark extractives was monitored for 24 weeks. Samples were taken from the middle, side and top of the pile. Each sample was extracted at 120 °C with both n-hexane and water, and the extracts produced were then analysed chromatographically using gas chromatography with flame ionisation or mass selective detection and high-performance liquid chromatography. The carbohydrates were next analysed using acidic hydrolysis and acidic methanolysis, followed by chromatographic separation of the monosaccharides formed and their derivatives. The results showed that the most intensive degradation occurred during the first 4 weeks of storage. The levels of hydrophilic extractives were also found to decrease drastically (69% in normal pile and 73% in snow-covered pile) during storage, whereas the decrease in hydrophobic extractives was relatively stable (15% in normal pile and 8% in snow-covered pile). The top of the piles exhibited the most significant decrease in the total level of extractives (73% in normal and snow-covered pile), whereas the bark in the middle of the pile retained the highest amount of extractives (decreased by 51% in normal pile and 47% in snow-covered pile) after 24-week storage.

Field monitoring of bearing capacity efficiency of permeable pipe pile in clayey soil: A comparative study

For clayey soil, an effective solution to accelerate pore water pressure dissipation after pile installation is using permeable pipe piles. But the differences in bearing capacity efficiency between permeable and normal piles are still unclear. In this paper, a series of load tests were conducted to compare their performance. The bare fiber Bragg grating (FBG) sensors were used to monitor and explore the pile-soil interaction process, together with pore water pressure and earth pressure cells. The FBG-based performance evaluation system provides an effective tool for the analysis of piles. The results show that the time required for the permeable pile to reach the ultimate bearing capacity was shorter than that of the normal one. The drainage holes did not lead to quality problems of the pile. The positive effect of drainage holes on the end-bearing resistance was gradually evident with time. This study provides valuable insight into the working mechanism of permeable pipe piles.

Impact of Inclined Load on the Performance of Under-Reamed Piles in Clay Soil

This research aims to study the behavior of under-reamed piles under the influence of inclined loads. Four piles of length 350 mm, 20 mm in diameter containing (0, 1, 2, and 3) of bulbs each one has 40 mm in diameter used, and they were inserted into stiff clay and sandy soils (CH and SP) so that the end of the pile sits on dense sandy soil, and the ultimate load capacity of the pile was calculated. The bearing capacity increase reaches more than 76% due to the presence of bulbs in a pile, and the increase reaches after there are two bulges to 15%. The lateral displacement of the pile was also studied by using the lateral load and the compound load and on four stages of the allowable load. The results showed that the effect of the compound load is limited in the normal pile, but in the under-reamed pile, the higher the vertical load, the less the lateral displacement. As for the moments resulting from the combined loads, the effect was up to 10% in the presence of an inclined load compared to the lateral load, and the effect of the presence of bulb in a pile near the ground level appeared to reduce the moments generated for the same load.

An Experimental Study on Laterally Loaded Winged Pile in Sandy Soil

Many offshore facilities such as offshore wind turbines and other engineering structures, including floating offshore facilities (FPSOs), are founded on or anchored with piles to transfer large horizontal loads relative to the imposed vertical load compared to onshore installations. The subgrade reaction of the soil surrounding the pile shaft mobilized when the lateral loading is applying on the pile to resist the applied loads. Since the soil at the midline is often weak and tends to have a poor subgrade reaction, resulting in large pile displacements near ground level. The lateral bearing capacity of pile foundations can be increased, and pile displacements near ground level can be decreased by expanding the piles’ cross-sectional area near the seabed level to compensate for the lower soil stiffness in the seabed level. One method of expanding the pile area in the lower soil stiffness zone is the addition of wings (or fins) near the seabed level. This paper presents a series of laboratory small-scale model tests that were conducted to laterally loaded piles with/without wings in sandy soil with different densities. The Piles slenderness’s ratio (L/D) is varied from 4, 6, 8, and 10 to simulate the behavior of both flexible and rigid pile designs, with different wings geometry and numbers. This study indicated that the lateral pile capacity increased, and the horizontal deformation of the pile decreased after mounting wings compared to the regular normal pile without wings. It has been found that the optimum geometry and number of adopted wings is found to be three wings, and its length equals (0.22) of the embedded pile length. The existence of wings improved the bearing capacity of the winged pile by 1.33, 1.18, and 1.16 for piles of L/D=10 in the case of loose, medium, and dense soils, respectively, compared to regular piles in the same condition.

Analysis of Stresses in Pile Caps by Finite Element.(Dept.

The behaviour of normal and shear stresses inside the body of squared pile caps, are studied by finite element F.E. The aim of the study is to give insight into the parameters affecting the stress distribution parameters such as, geometrical properties of the cap, different loading conditions (concentric, inclined, eccentric in one two directions), and different supporting conditions (normal piles and large piles are considered). Three dimensional elastic body was used to represent the pile cap while point supports were used to represent the piles.

Investigation of the penetration characteristics of snake skin-inspired pile using DEM

Snake can perfectly utilize its scales to move. Inspired by the snake scales, this study investigated the characteristics of the snake skin-inspired pile penetration process. Six kinds of pile shaft inspired by snakeskin and one normal pile as reference were designed. In order to investigate the influence of scale layouts on the pile and particle responses, the discrete element method was adopted to simulate the process of pile penetration numerically. Effects of three potentially relevant factors, including the scale height, scale length and penetration direction were analyzed. According to the computed results, the snake skin-inspired pile has a greater shaft resistance, causes obvious soil disturbance with aspect to soil displacement and particle rotation compared with the reference pile. The shaft resistance and soil disturbance are positively correlated with the scale height, and inversely relevant with the scale length. The inspired pile installed in cranial direction causes a wider disturbance range in surrounding soil compared with the caudal installation. The cranial penetrated pile contributes to significant soil dilatancy, leading to greater loading–unloading behavior and less major principal stress rotation of surrounding soil.

Settlement analysis of pile cap with normal and under-reamed piles

The use of pile foundations has become more popular in recent years, as the combined action of the pile cap and the piles can increase the bearing capacity, reduce settlement, and the piles can be arranged so as to reduce differential deflection in the pile cap. Piles are relatively long, slender members that transmit foundation loads through soil strata of low bearing capacity to deeper soil or rock strata having a high bearing capacity. In this study analysis of pile cap with considering different parameters like depth of the pile cap, width and breadth of the pile cap, type of piles and different types of soil which affect the behaviour of pile cap foundation is carried out by using Finite Element Software ANSYS. For understanding the settlement behaviour of pile cap foundation, parametric studies have been carried out in four types of clay by varying pile cap dimensions with two types of piles namely normal and under-reamed piles for different group of piles. Furthermore, the analysis results of settlement and stress values for the pile cap with normal and under-reamed piles are compared. From the study it can be concluded that settlement values of pile cap with under-reamed pile are less than the settlements of pile cap with normal pile. It means that the ultimate load bearing capacity of pile cap with under-reamed piles are greater than the pile cap with normal piles.

Study of fin shape on the behaviour of finned piles under combined loading conditions

Several types of structures, such as bridge abutments, retaining walls, transmission line towers and other structures exposed to wind and earthquake loads, supported by pile foundation are being subjected to large lateral loads. Finned pile is an emerging form of pile foundation that is capable of resisting large lateral displacements. Here, it is attempted to assess the effect of the shape of fins on the lateral carrying capacity of a pile with fins subjected to combined loading conditions. Small-scale laboratory model tests were performed on normal piles (without fins) and also with finned piles. These piles were embedded in sand. The studies were carried out by varying the geometric factors such as length, width and shape of the fins. Results show that there is a substantial increase in lateral resistance capacity of the piles after fitting the fins close to the pile head. The increase in lateral resistance capacity gained by placing fins on a pile varies with dimension of the fins. On the basis of the laboratory model test results, optimum dimension of the fin for maximum improvement are recommended for combined loading conditions. The trend showed in the results were comparable with those reported in the literature as on studies with lateral load alone.

Model study on the performance of single-finned piles in clay under lateral load

Generally, foundations of many structures, such as transmission towers, bridge abutments, ocean engineering structures, marine dolphins, dock-fendering systems, and moorings are subjected to different modes of lateral loading. This research aims to study an alternative and novel technique to improve the lateral pile capacity in clay using fins at the top of piles. Laboratory small-scale model tests were carried out to study the behavior of laterally loaded finned piles installed in clay soil for different undrained shear strengths (Cu = 11 and 15 kPa). The effects of different factors, such as pile type, stiffness, geometric dimensions, and shapes of fins, were studied. Moreover, the effects of the fin number and inclination angle were also investigated. Results emphasized that there is an increase in the lateral pile resistance against the lateral load after placing fins at the top of the pile head. It has been found that the optimum length of the adopted fins should equal 0.4 of the pile embedded length and the fin width should equal the pile diameter. The existence of fins improved the behavior of finned piles by 1.67 and 1.55 for piles of L/D = 10 in the case ofCu = 11 and 15 kPa, respectively, compared to regular normal piles in the same condition. Also, the improvement in L/D = 22 piles due to fins reached to 1.29 and 1.35 for the case of Cu = 11 and 15 kPa, respectively.

New interaction model for the annular zone of stepped piles with respect to their vertical dynamic characteristics

Stepped piles with a larger section at the top have been increasingly used as foundations for bridge abutment in China. In this paper, numerical modelling using ABAQUS is firstly carried out to investigate the behavior of a annular zone below the top larger section. Then, a new interaction model with a wedge-shaped soil below the annular zone is proposed for pile–soil system. In the model, the soil wedge and normal pile segment were treated as a generalized pile segment. By combining the Novak plane strain model and Rayleigh-Love rod theory, the dynamic characteristics of a stepped pile subject to a vertical harmonic excitation at the pile head are theoretically investigated. The analytical solutions are deduced using Laplace transform and impedance function transfer method. The proposed model is verified by the sensitivity analysis of the soil wedge dimension and comparison with FEM results. Compared with the conventional Voigt model, the present solution shows a flatter oscillation in complex impedance curves, indicating that the Voigt model may overestimate the dynamic response of stepped piles. Finally, selected results are presented to examine the influence of pile geometry on the vertical dynamic responses.

PERFORMANCE OF LATERALLY LOADED MODEL FINNED PILES IN CLAY SOIL

Finned piles are a novel pilling technique which is used as a foundation for many structures such as: transmission towers, bridge abutments, ocean engineering structures, marine dolphins, dock-fendering systems and moorings that subjected predominantly to both laterally loads beside the vertical loads.This paper presents a series of experimental tests that were conducted to lateral loaded piles with/without fins in clay. Piles with different types were fitted with different fins geometry and numbers. The results of this study indicated that the pile lateral capacity increased and the horizontal deformation of pile decreased at thesame load level after mounting fins is compared to regular normal pile without fins. It has been found that the optimum geometry of adopted fins is found to be its length equals to (0.4) of the embedded pile length and width equals to the pile diameter. The existence of such fins considerably increased the ultimate lateral capacity by as much as (54% and 35%) of it is initial value for short and long piles respectively.

Field Test and Numerical Simulation on Bearing Capacity of Squeezed Branch Pile in Transmission Line

By applying static load tests and the finite element analysis method, this study assesses the load-bearing performance and load transfer mechanism of squeezed branch piles. This study also compiles data and discusses findings about the distribution of field displacement, the development of a plastic zone in the soil, and the influence of branch quantity and horizontal load on the vertical bearing capacity. The results show that the axial force of the squeezed branch pile changes obviously at the site of the squeezed branch. Additionally, this study identifies the sequenced effects of frictional resistance; the displacement patterns of the soil around the pile, particularly below the branch and pile tip; the minimum center distance between piles in a group, which should be greater than 1.5 times the branch diameter; and the location of plastic strain in the soil below the branches and pile tip. The data reveal that the vertical bearing capacity of squeezed branch pile is 16 to 30% higher than that of normal pile under the same conditions; furthermore, the vertical bearing capacity of squeezed branch pile increases as the number of branches and horizontal load increase. Considering geological engineering conditions and loading requirements, it is advisable to identify an optimum branch quantity for the specific bearing stratum; in this case, the optimum branch quantity was 1 to 3．DOI: http://dx.doi.org/10.5755/j01.mech.23.5.19357

Compressive and flexural behaviour of reinforced concrete permeable piles

Abstract Driven piles generate excess pore water pressures in the surrounding soil, where a full dissipation of these pressures may take a very long time. Measures are therefore sought to accelerate soil consolidation. The concept of permeable pile with drainage holes around the circumference of pipe pile could serve this purpose by providing drainage paths. However, the structural integrity of permeable pile may be deteriorated due to these openings. This paper presents the results of uniaxial compression and flexural tests on permeable and normal pile specimens. The influence of concrete strength and pattern of drainage holes in terms of diameter, total number and layers on the ultimate compressive strength is investigated. The crack pattern, deflection profile and concrete strains are measured for both normal and permeable piles. It has been found that drainage holes could cause the reduction in ultimate compressive strength, but the measured values are still far greater than design estimations. Moreover, the permeable piles have higher flexural capacity than the normal piles due to the stress redistribution.

Model Study on the Performance of Single-Finned Pile in Sand under Tension Loads

AbstractA variety of structures similar to marine dolphins, dock-fendering systems, tower foundations, inundated platforms, and abutments are installed on deep foundations, which are subjected to uplift loads. This paper introduces a modern pile-modification strategy known as finned pile that increases pile-tension capacity by providing an affirmative anchorage close to the pile tip. The alteration consists of four fins welded at the bottom of a pile around the circumferential area. Comparative small-scale model uplift tests were performed on normal piles without fins and on piles with fins. Investigations were done by changing the fin-width ratio (b/D), fin inclination angle (β), pile length-to-diameter ratio (L/D), and soil density. Results indicate that there is a considerable increase in uplift capacity of the piles when using fins at the end of the piles. When fins were installed with effective width equal to the pile diameter and at an inclination angle (β) of 90° for sand, with relative density (Dr...

Settlement analysis of rectangular piles in nonhomogeneous soil using a Winkler model approach

SUMMARYAn analytical approach using a Winkler model is investigated to provide analytical solutions of settlement of a rectangular pile subjected to vertical loads in nonhomogeneous soils. For a vertically loaded pile with a rectangular cross section, the settlement influence factor of a normal pile in nonhomogeneous soils is derived from Mindlin's solution for elastic continuum analysis. For short piles with rectangular and circular cross sections, the modified forms of settlement influence factors of normal piles are produced taking into account the load transfer parameter proposed by Randolph for short circular piles. The modulus of subgrade reaction along a rectangular pile in nonhomogeneous soils is expressed by using the settlement influence factor related to Mindlin's solution to combine the elastic continuum approach with the subgrade‐reaction approach. The relationship between settlement and vertical load for a rectangular pile in nonhomogeneous soils is available in the form of the recurrence equation. The formulation of settlement of soils surrounding a rectangular pile subjected to vertical loads in nonhomogeneous soils is proposed by taking into account Mindlin's solution and both the equivalent thickness and the equivalent elastic modulus for layers in the equivalent elastic method. The difference of settlement between square and circular piles is insignificant, and the settlement of a rectangular pile decreases as the aspect ratio of the rectangular pile cross section increases. The comparison of results calculated by the present method for a rectangular pile in nonhomogeneous soils has shown good agreement with those obtained from the analytical methods and the finite element method. Copyright © 2014 John Wiley & Sons, Ltd.

Numerical Simulation on the Regular Pattern of the Lateral Friction Transmission of the Pile in the Incline under the Pulling Force

The regular pattern of the lateral friction transmission is one of the most critical influences on the ultimate uplift bearing capacity. The pile foundation in the incline under the pulling force has a wide variety of characteristics which is different with the normal pile. Numerical simulation is done by the use of FLAC3D in this paper. The regular pattern of the lateral friction transmission of the pile in the incline under the pulling force is studied. And the influence factors on the lateral friction transmission such as the slope gradient, the length and location of piles are discussed. The results show that the incline has a great influence on the lateral friction transmission. The lateral friction which is away from the incline-side is about 30% to 50% bigger than the incline-side. The slope gradient and the location of piles all have a great influence on the lateral friction transmission.

Model Test Studies of the Vertical Bearing Behavior of Bored Piles with Breakage Defects

In order to study the vertical bearing behavior of bored piles with breakage defects, a series of methods for simulation of normal piles and broken piles in laboratory was developed and used to investigate the vertical bearing behavior of these piles. The load-settlement curves of normal piles and broken piles were measured and analyzed. The tests revealed that the upper part of a broken pile works alone as a short pile before it contact with the lower part of the pile at the end of the first sudden drop stage.The analysis of the test results showed that the position of the breakage defect has a great influence on the lost in vertical bearing capacity of the pile.

A Nonlinear Numerical Analysis of Vertical Bearing Behavior of Bored Pile Foundations Including Defective Piles with Stem Shrinkage

In order to investigate the influence of the defective piles with stem shrinkage on the working behavior of pile foundations under vertical loadings, a numerical model was set up for the analysis of pile foundations. A series of contrastive analyses were made to a group piled foundations including a pile with defect of stem shrinkage in a shallow or a deeper depth and a pile foundation with normal piles with a three dimensional nonlinear finite-infinite element method. The basic working behavior of the pile foundation with a defective pile of stem shrinkage was initially revealed by the results of the analyses; and the basic rules of the affects of pile stem shrinkage defect on the distribution of axial forces among piles and the bending moments in pile caps were obtained. The results of this research are not only helpful for the understanding and rational judgment of the working mechanism, but also of practical importance in the assessment of the bearing behavior of pile foundations including defective piles with stem shrinkage and in the structural designs of piles and pile caps.

Research on Load Transfer Model of Super-Long Single Pile

Currently, super-long piles are designed based on the theory of normal long piles. There is no recognized reasonable mechanical model for qualitative analysis. In this paper, based on load transfer function method, an improved load transfer model is proposed, which gives consideration to both the degradation of skin friction and the asynchronous work between lateral friction resistance and pile-tip resistance caused by pile-soil slip. By applying it in various working conditions, the corresponding pile-soil displacement and axial force of super-long piles are derived. Finally, the proposed model is validated by comparing its analytical solutions to the results of FEM and practical survey of super-long piles, and it provides a new efficient approach for the study of the mechanical behavior of super-long single pile.