Pile Tip Research Articles

Bearing Capacity and Deformation Behaviour of Branch Pile

The working mechanism of branch pile under vertical load is studied based on digital image correlation method in model test. Bearing capacity and deformation characteristics of equal-diameter pile and branch pile are obtained during the analysis. The study results show that the bearing capacity of branch pile is higher than that of the equal-diameter pile. The displacement field around equal-diameter pile is divided into the pile side and pile tip deformation regions, destruction pattern of single pile is similar to the Meyerhof's destruction pattern. Soil beneath branch generates a shear sliding surface under the ultimate load, and the soil beneath pile tip shows a pricking destruction pattern.

Research on Dynamic Impedance Function for Horizontal Vibration of Single Pile

The horizontal vibration characteristic of the pile foundation is a key technology in dynamic design of foundation engineering. By researching on the horizontal harmonic loads in layered foundation, use horizontal vibration answers of buried foundation to deal with horizontal vibration impedance problems of pile tip. The transition matrix can be used to analyze the dynamic impedance function for horizontal vibration of pile foundation in layered foundation. And results in the paper is checked with traditional methods, which shows the both results fitting well.

Ground Movement during Concrete Pipe Piles Jacking in Silt Deposit

In this study a comprehensive field test program was carried out to closely monitor the ground responses during open-ended concrete pipe piles jacking into a deposit mainly consisting of silt soils. The horizontal soil movement due to pile jacking was of depth-dependent characteristic that cylindrical cavity expansion models were unable to capture. The magnitude of displacement decreased rapidly with depth, and no discernible deflection was measured below the depth of the pile tip. The maximum displacement along the depth occurred at clayey-silt layer with relative lower permeability. The rebound of soil movement may be attributed to the setup effect following the piling stage.

Numerical Simulation of Deformation Pattern to Pile Raft Foundation

ABAQUS is used to study the load-settlement characteristic and soil displacement field of the pile raft foundation. Numerical results are compared to the outputs from model test. The study results show that good consistency is obtained from the comparison of results between numerical simulation and model tests. Small pile space will weaken the single pile bearing capacity. The compress region is mainly centralized in the soil beneath the pile tip to the 3b space pile raft foundation, which presents a massive deep foundation failure pattern. As the increase of pile space, the compress region under cap shifts upward. The displacement influence depth of 6b space pile foundation is smaller than 3b space pile raft foundation, and it is destroyed by the lateral squeeze of the soil around piles.

풍화암소켓 대구경 현장타설말뚝의 선단보강그라우팅 사례

현장타설말뚝의 포스트그라우팅 기법은 말뚝 시공시 발생하는 슬라임과 굴착으로 인해 교란된 원지반을 압축 및 보강함으로써 기초의 선단지지력을 현저히 증강시키는 것으로 알려져 있다. 그러나 현재까지 국내외적으로 통용되는 설계지침 또는 시방은 없는 상태이며, 특히 국내에서는 말뚝 포스트그라우팅 기법이 설계지지력 증강 목적이 아닌, 소요지지력에 미달되는 말뚝에 대한 보수보강의 개념으로 이해되고 있어, 그 효과에 비해 관련 연구 및 실용화 실적이 미비한 실정이다. 본 연구에서는 포스트그라우팅 기법의 국내 풍화대소켓 현장타설말뚝에의 적용성을 검증하기 위해 풍화암 근입 대구경 현장타설 콘크리트말뚝 시공 현장을 선정하여 포스트그라우트 시험시공을 실시하였다. 또한 포스트그라우팅 말뚝, 그리고 인접한 미보강 말뚝에 대한 정재하시험을 수행함으로써, 포스트그라우팅이 현장타설말뚝의 축방향 지지력 증강에 미치는 효과를 정량적으로 비교분석해 보고자 하였다. 정재하시험 결과, 선단보강 말뚝 선단하중-침하곡선의 초기기울기가 미보강 말뚝 선단히중-침하곡선의 기울기에 비해 4배 이상 증가였으며, 허용침하량(1%D) 기준으로 보강 및 미보강 말뚝의 선단지지력은 각각 12.0MPa, 7.0MPa로 나타나, 포스트그라우팅 적용 후 말뚝의 허용선단지지력이 70% 이상 증가하는 것을 확인하였다. Post-grouting for the drilled shaft is known to remarkably increase the end bearing capacity of pile by consolidating and reinforcing the disturbed ground containing slime around the pile tip. However, the general design guideline for post-grouting has not been established yet in Korea. Especially in the domestic application, the post-grouting is employed just for repairing the pile with unacceptable resistance rather than for increasing the design resistance of pile. Therefore, little is reported about the effect of post-grouting on the pile resistance itself. In this study, the effect of post-grouting on the resistance of drilled shafts installed in the weathered rock in Korea was estimated by performing the bi-directional load tests on the piles with and without the post-grouting. The test results presented that the initial slope of end bearing-base displacement curve in the pile with post-grouting was 4 times higher than that without post-grouting. At the acceptable settlement (1% of pile diameter), the end bearing capacities of piles with and without the post-grouting were estimated to be 12.0 MPa and 7.0 MPa, respectively, which indicate that the post-grouting could increase the end bearing resistance of pile in weathered rock more than 70%.

Comparative Study on Bearing Performance between Y-Section Pile and Conventional Pile

Y-shaped vibro-pile (referred to as Y-Section pile) is a newly developed pile based on traditional circular driven cast-in-place pile and the principle of peripheral expansion of various shapes with constant cross-section. Three-dimensional numerical model is built for Y-Section pile, circular pile, square pile and triangular pile with the same sectional area using finite element software ABAQUS. The pile material is elastic model as well as soil around pile and under pile is Mohr-Coulomb model. With the same cross-sectional area and under the same load, the settlement of Y-Section pile is the smallest, followed by triangular pile, square pile and circular pile in sequence; the average stress of pile-end soil of square pile is the greatest, followed by triangular pile, circular pile and Y-Section pile; the ultimate bearing capacity of Y-Section pile is the largest, followed by triangular pile, square pile and circular pile. Assuming that the lateral friction is of linear growth along pile shaft and of triangular distribution, the maximum lateral friction intensity at pile tip is different for various piles with the same cross-sectional area, and the largest is circular pile, followed by square pile, Y-Section pile and triangular pile. The maximum lateral friction intensity of Y-Section pile is up to 88.71% of circular pile and there is friction resistance weakening with various shapes.

Test and Finite Element Analysis on Dynamic Characteristic about Ultra-Long Bored Pile

The present standards for designing of ultra-long pile exist the contradiction between theory and practice; By combining the projects and finite element calculation and analyzing the characteristics of force and deformation, we can get the conclusion that there is asynchronous nature between the side resistance and the tip resistance in different soil layers. Meanwhile, the pile tip resistance has not been fully realized. To solve the above problems, I put forward reasonable proposals in order to make up for the deficiencies in designing. Introduction

Study on Bearing Characteristics of Large Diameter and Long Rock-Socket Pile of Beipan River Bridge

Beipan River Bridge is located on the Beipan River Grand Canyon in the middle of Yunnan-Guizhou Plateau. The bridge pile, diameter of 2.8m, subjects to the vertical load design value of 58000KN, the thickness embedded in the breeze rock more than 85% of pile, was almost a full rock-socket pile, its bearing load was large and embedded in rock deeply. Based on test method of self-balancing, the bearing characteristics of large-diameter rock-socket pile in argillaceous area have been analyzed, including the axial force of pile, side friction, the tip resistance and so on. The results indicated that the bearing characteristics of the part in sock was as same as the friction piles in muddy dolostone area; From the results of test the side friction of pile could be estimated higher in strong weathering argillaceous dolomite area while the friction in weak or puny weathering muddy dolostone was relatively close to the value of exploration reports. Pile tip resistance had a greater potential. Finally, analyzed the measured curve, it could be seen that the calculation of bearing capacity was less than the test result, and the pile foundation was safety enough.

Performances of Compressive Capacity for Belled Wedge Pile Group

The belled wedge pile, which can improves the friction of pile shaft, tip resistance and reduce the influence of negative skin friction, is introduced. In this paper, the accuracy of FLAC3Dmodel is verified with field load test results. Subsequently, the numerical model was used to study the compressive behavior of belled wedge pile, conventional belled pile, wedge pile, and uniform section pile with the same concrete volume. Furthermore, the compressive behavior of belled wedge pile group was studied in terms of influencing factors such as pile spacing, stiffness of soil at the pile end, and diameter of enlarged pile head. The numerical results show that the compressive advantages of belled wedge pile can be developed adequately when the distributions of the friction of pile shaft and pile tip resistance are equilibrium, and it increases with increasing pile spacing, increasing stiffness of soil at the pile end, and increasing diameter of the enlarged pile head.

파일길이비와 암반층의 위치에 따른 마이크로파일 설치방법

본 연구는 토사지반 또는 유한심도 내 암반층이 있는 지반을 대상으로 마이크로파일의 효과적인 설치방법을 제안하고 제안된 설치방법의 적용성을 평가하기 위해 수치해석을 수행하였다. 해석결과, 지반에 설치된 파일이 강체거동을 하는 경우는 파일 선단부와 암반층 위치 따라 파일 보강지반 지지력이 달라지나, 연성거동을 하는 경우는 파일 선단부와 암반층의 위치보다 파일강성과 관련한 파일 설치길이와 파일 근입길이에 따라 지지력이 달라지는 것으로 나타났다. A numerical analysis has been conducted to propose the effective installation methods of Micro-pile in a sandy soil or a soil with rock layer. As a result, the bearing capacity of reinforced soil by rigid Micro-pile has influence on a connection state of the tip of pile and surface of rock layer. But that by flexible Micro-pile has more influence on a penetration length of pile than the connection state of the tip of pile and surface of rock layer.

Performance of Cement-Fly Ash-Gravel Pile-Supported High-Speed Railway Embankments over Soft Marine Clay

The Beijing-Tainjin high-speed railway were constructed between two major cities in China. Since part of the railway is over soft marine clay, appropriate ground improvement, cement-fly ash-gravel piles, was selected to improve the soft marine clay to meet technical requirements for the high-speed railway. This article presents the field measurements in the railway embankment project including the load distribution between soils and piles, excess pore pressure, and settlement and lateral displacement. The test results show that the stress concentration to the piles reduced the excess pore pressure effectively. The proportion of the load carried by soils was small, and thus the settlement was significantly reduced. The compression of the rigid piles contributed to less than 21% of the total settlement. The majority of the settlement was contributed by the penetration of the piles and the compression of the soft soil below the pile tips. The average compression thickness below the pile tips was 22 m, which is equivalent to one times the width of the treated area. The measured differential settlement of the embankment was approximately 3 mm.

A destructive field study on the behavior of piles under tension and compression

This paper involves a series of destructive full-scale load tests on long bored piles instrumented with strain gauges along the shafts, including two compression and two tension loading tests. The load-displacement response, axial force, skin friction, and the thresholds of the slip displacement for fully mobilizing the skin resistances in different soils are discussed. Moreover, the theoretical solution for estimating the pile tip settlement under compression was adopted to analyze the test results. It was found that the measured skin frictions for the piles under compression were about 6% to 42% higher than the estimated values of the cone penetration tests (CPTs), whereas the measured skin frictions in the uplift cases were about 16% to 50% smaller than the estimated values. In addition, the average limited skin frictions for the tension piles were about 0.36 to 0.78 times the average ultimate skin frictions for the piles under compression. It also can be indicated that the skin friction along the pile depth approached the limited state, and decreased from a peak value with increasing loads.

Increasing the Resistance of Piles Subject to Cyclic Lateral Loading

Small-scale tests were carried out on a monopile and fin piles to determine the effect the length of fins had upon the lateral displacement of cyclically loaded piles. A variety of loading conditions were applied to model piles in a dense sand by using a mechanical loading system. Ten thousand cycles were used in each test to represent 20 years of environmental loading on offshore structures. Variables included the magnitude, frequency, and direction of the load; the type of pile tip; and the length of the fins. The reduction in pile head displacement was used as a measure of the efficiency of the fins. The tests show that the fins reduced the lateral displacement by at least 50% after 10,000 cycles.

EFFECT OF STRENGTH AND TIP LENGTH OF ENLARGED GROUTED BASE ON BEARING CAPACITY OF NODULAR PILE

Vertical loading tests were performed on the enlarged grouted base of nodular pile using pressurized sand tank for studying the effects of strength of enlarged grouted base and the length between the pile tip and tip of enlarged grouted base on the pile bearing capacity. The main conclusions based on the studies are as follows. 1) When the tip length was zero and the strength of enlarged grouted base was greater than 10 N/mm2, the bearing capacity was equivalent to the case when the strength was 20 N/mm2 until the settlement reached 10% of the pile diameter. 2) When the strength of the enlarged grouted base was 15 N/mm2, there was no effect of the tip length on the load-settlement curve. 3) For all cases, even when the enlarged grouted base failed, the bearing capacity continued to increase.

Effects of the Construction Method on Pile Performance: Evaluation by Instrumentation. Part 2: Experimental Site at the Faculty of Engineering of the University of Porto

. Three different types of piles (bored, CFA and precast driven) were installed in the experimental site located in the Campus of the Faculty of Engineering of the University of Porto to study the effects of the construction method on pile performance. The subsoil is a residual granitic soil reaching depth levels over 20 m. In this site, several field and laboratory tests were conducted to obtain the local geotechnical parameters. Static pile load tests with load-unload cycles were performed. Bored and CFA piles were instrumented along the depth, with installation of retrievable sensors; a flat-jack load cell was inserted at the bottom of the bored pile. Load tests results demonstrated that bored and CFA piles show similar behavior: i) the applied load reaching the pile tip was about 42%, ii) and the average mobilized lateral resistance was about 60 kPa. After the tests were completed, piles were extracted for further inspection of shaft and load cell conditions. The driven pile although having a smaller cross-section showed a stiffer response and higher resistance than the other two piles, which are a clear indication that the installation effects play an important role in the pile response. The results are compared to those obtained in Part 1 of this article relating to tests performed at the Experimental Field of Unicamp (State University of Campinas).

Response of tapered piles in cohesionless soil based on model tests

This paper describes model tests of different types of tapered piles in cohesionless soils. Chromium plated three steel piles, one straight and two taper-shaped piles of same length and pile tip diameters have been executed for pile loading test in a downward frictional mode. Two different types of model grounds have been prepared for the test. Relative densities of 80 % and 60 % have been modeled to penetrate piles in two different types of sands to observe the effectiveness of skin frictions of different types of piles. The response of tapered piles has shown that the skin friction has increased with increasing the tapering angle at normalized settlement ratio of 0.4. High density ground yields higher skin friction when the maximum tapered pile was penetrated. Slightly increased tapering angle of the pile affects remarkably on the skin friction with compared to conventional straight cylindrical pile even at small 0.1 settlement ratios.

基礎杭打設による海面処分場の底面遮水工に与える短期的影響（杭先端部）の考察

基礎杭打設による海面処分場の底面遮水工に与える短期的影響（杭先端部）の考察

Mobilized side and tip resistances of piles in clay

This paper presents a procedure to assess the mobilized pile side and tip resistance versus pile head and tip settlement under axial load in clay soil. The load transfer ( t– z) curve is evaluated at any point on the loaded pile based on the combined pile tip/side resistance–displacement mechanisms along the length of the pile. Unlike current methods that assume the pile settlements as a percentage of the pile/shaft diameter, the presented technique determines the side and tip resistance of the pile and the associated pile settlement under existing load based on the current stress/strain level in the surrounding soil up to failure (excessive settlement). The technique employs the concepts of the elastic theory and Ramberg–Osgood characterization of the stress–strain behavior of the clay soil. Case studies are also presented to exhibit the capabilities of the proposed procedure. The good agreement between measured and calculated load transfer curves along the pile and pile tip resistance versus pile head, side, and tip displacements shows the consistency of the proposed procedure. A computer code is developed to employ the presented technique.

Reliability-based calibration of resistance factors for static bearing capacity of driven steel pipe piles

As part of a study to develop load and resistance factor design (LRFD) codes for foundation structures in South Korea, resistance factors for the static bearing capacity of driven steel pipe piles were calibrated in the framework of the reliability theory. A database of 52 static load test results was compiled, and the data from these load test piles were sorted into two cases: a standard penetration test (SPT) N-value at pile tip (i) less than 50 and (ii) equal to or more than 50. Reliability analyses and resistance factor calibration for the two static bearing capacity analysis methods adopted in the Korean Design standards for foundation structures were performed using the first-order reliability method (FORM) and the Monte Carlo simulation (MCS). Reliability indices and resistance factors computed by the MCS are statistically identical to those computed by FORM. Target reliability indices were selected as 2.0 and 2.33 for the group pile case and 2.5 for the single pile case. The resistance factors recommended from this study are specific for the pile foundation design and construction practice and the subsurface conditions in South Korea.

Non-destructive test for pile beneath bridge in the time, frequency, and time-frequency domains using transient loading

The main objective of this paper is to evaluate the capabilities of non-destructive test (NDT) methods by using transient loading, i.e. the sonic echo (SE) method in the time domain and the impulse response (IR) method in the frequency domain, in detecting the pile length in the foundations of bridges. Methods such as these, which are based on transient elastic waves, have been used for many years. However, several drawbacks have been described in the literature, including difficulties with the installation of the testing devices. In this paper, several experimental studies were carried out on existing scoured bridge pile foundations. In order to overcome environmental limitations, the Ultrasonic Pulse Velocity method was adopted, and the installation procedure for the testing devices was modified. Moreover, a recently developed numerical signal processing tool, the Wavelet Transform (WT), was adopted to interpret the testing signal in the time-frequency domain. The results indicate that the modified testing procedure is feasible for in-service pile integrity tests. The processed signal clearly and visually illustrates the temporal changes, and the pile tip can be highlighted in the time-frequency domain. The depth of the scour pile tips can be detected precisely with the proposed modified device installation and the improved numerical signal processing. The results in the time-frequency domain are also consistent with traditional SE/IR testing methods.