Pre-stressed High-strength Concrete Pipe Piles Research Articles

Field and Numerical Study of the Bearing Capacity of Pre-Stressed High-Strength Concrete (PHC)-Pipe-Pile-Reinforced Soft Soil Foundations with Tie Beams

Pre-stressed high-strength concrete pipe piles (PHC pipe piles) have been widely used in actual soft foundation treatment projects due to their reliable quality, fast construction, assembly line production, and environmental friendliness. However, large-scale slip damage still occurs in construction projects. In order to reduce and avoid such accidents, a highway in Guangdong (section K31+100~K31+388) was taken as an example for this study. Plaxis 2D software (V22.01.00) was used to establish a PHC pipe pile composite roadbed model and investigate the effects of tie beam form, pile lengths, pile spacings, pile verticality, and embankment filling loading modes on the settlement and stability of the composite roadbed. The results show that the original treatment plan, which had the form of a PHC pipe pile with caps, had a low horizontal bearing capacity and a poor anti-disturbance ability, leading to the occurrence of a landslide accident. A comparison of different structural forms revealed that the longitudinal and transverse tie beam form was the most stable, followed by the transverse tie beam form, longitudinal tie beam form, PHC pipe pile form with caps, and PHC pipe pile form without caps. Compared to the structural form of PHC pipe piles with pile caps, the stabilities of the transverse tie beam form and the longitudinal tie beam form were improved by 42.47% and 38.61%, respectively, while that of the longitudinal and transverse tie beam form was improved by 50.87%. The application of longitudinal and transverse tie beams effectively reduced the settlement of the composite roadbed, as confirmed by both measured data and finite element analysis. This structure achieved the desired vertical settlement control and lateral anti-slip effects.

Multi-scale microstructure quantitative characterization and anti-erosion performance of PHC pipe pile

Pre-stressed high-strength concrete (PHC) pipe pile is widely used in many large-scale projects, thus their durability has attracted more and more attention. However, in most studies, PHC pipe pile is regarded as the same as ordinary reinforced concrete, ignoring the effect of special construction processes and hollow shape on its microstructure and anti-erosion performance. In this paper, the real PHC pipe pile was cored and cut to investigate the multi-scale microstructure and the anti-erosion performance of PHC pipe pile concrete layer. The results shown that pore content first increases and then decreases with PHC pipe pile from the outer layer to the inner layer (5F → 1F) by CT, BSE and LF-NMR results, and the pore content changes most significantly around the rebar in PHC pipe pile. In rebar interfacial transition zone (ITZ), the thickness of the voids in PHC pipe pile is greater than that of normal reinforced concrete under the same water-binder ratio condition. Additionally, the content of un-hydration products in aggregate ITZ is obviously greater than that in rebar ITZ. Furthermore, the chloride ion diffusion coefficient of the concrete on the outside of the PHC pipe pile is slightly larger than that on the inside, which is closely related to the higher pore connectivity of the concrete on the outside of the PHC pipe pile. Moreover, it was found that centrifugation can not only reduce the water-binder ratio of PHC pipe pile but also affect the radial pore structure of PHC pipe pile concrete, including porosity and pore connectivity. This work finally indicated that the microstructure of PHC pipe pile concrete is quite different from that of normal reinforced concrete, providing a theoretical basis for establishing the diffusion model of PHC pipe pile concrete.

Shake-table test on dynamic response of prestressed high-strength concrete pipe piles under Soil–Structure interaction

This paper presents the results of a shake-table test on a superstructure model supported by a prestressed high-strength concrete (PHC) pipe pile in soft soil. The primary objective is to investigate the dynamic response of the PHC pipe pile in soft soil influenced by soil–structure interaction (SSI). Accordingly, a single PHC pipe pile with iron blocks is constructed and embedded in soft soil. First, the production of the physical model of the PHC pipe pile and experimental details are elucidated. Then, the study focuses on the dynamic response of the soil–pile–superstructure system considering different ground motion types and peak ground accelerations (PGAs). Finally, the inertial and kinematic effects on the dynamic response of the PHC pipe pile are analyzed. The results show that the SSI effect can increase the predominant period of the superstructure. With the SSI effect, the seismic design should consider the adverse effects of long-period and pulse-type ground motions on the pile. The SSI effect caused the rate of increase in the pile bending moment to be gradually higher than the increase in PGA. Moreover, the dynamic response of the PHC pipe pile is mainly dominated by the inertial effect.

Experimental research on the flow law of the grouting fluid in an annular gap between a non-soil-squeezing PHC pipe pile wall and a hole wall

The bearing capacity of drilling with pre-stressed concrete pile cased pile (hereafter referred to as DPC pile) is closely related to the grouting effect on an annular gap between a pre-stressed high-strength concrete (PHC) pipe pile wall and a hole wall (hereafter referred to as the an annular pile–soil gap). A physical grouting model testing system for the DPC pile based on a high-precision three-dimensional (3D) scanner and a multi-functional grouting box has been independently developed. In this method, 3D geometric size and spatial point information of the grouting stone have been quantitatively characterized. The influences of the water–cement ratio, grouting pressure, collapsed holes, and falling sand have been studied. The conclusions are obtained as follows: (1) a quantitative characterization method of the 3D geometric dimensions of the grouting stone based on a 3D scan is accurate and reliable and can overcome the shortcomings of traditional manual measurement. (2) In the same horizontal plane, grouting body thickness gradually decreases as its horizontal distance from the grouting outlet increases, and the higher the elevation, the greater the rate of decrease; conversely, the lower the elevation, the slower the rate of decrease. When the horizontal distance from the pulp outlet is equal, slurry thickness gradually decreases as the height increases. (3) For the grouting liquid with a water–cement ratio of 0.5, grouting pressure should not be less than 0.6 MPa. (4) When the falling sand is not far above the grouting outlet, a grouting root system can be formed, whose grout veins, complexity, and grout coverage area can be optimally improved by changing the fluidity of the grout and grouting pressure. When the falling sand is on the side of the grouting outlet or the surface of the grouting outlet but far away from the grouting outlet, it is easy to be avoided by the grout, which can greatly reduce the grouting effect.

Research on Dynamic Pile-Driving Formula Parameters and Driving Feasibility of Extra-Long PHC Pipe Piles

Prestressed high-strength concrete (PHC) pipe pile has the advantages of high single pile bearing capacity, a wide range of applications, good driving resistance, fast construction speed, etc. It has been widely used in high-rise buildings, bridges, ports, and other industries. The application of extra-long PHC pipe piles with a length of more than 50 m is increasing. However, there are few studies on the drivability and hammering criteria of extra-long PHC piles. To analyze the drivability of extra-long piles and predict their bearing capacity, in this paper, high-strain dynamic tests were carried out on 14 test sections with the pile foundation of Temburong Bridge in Brunei as the research background. The hammer stop control criteria calculated according to the Hiley formula would lead to excessive hammering. Three types of damage occurred during construction: pile shaft breakage, weld tearing, and pile head breakage. The weight and drop height of the piling hammer selected for this project were appropriate, and the extra-long test piles can be hammered to the design depth. The values of Cp (Compression of the pile) and n (the efficiency of the blow) were fitted based on the dynamic test data, which provided a more accurate reference for the selection of subsequent piling parameters of the project. It provides a more accurate calculation method for predicting the bearing capacity of extra-long PHC piles and provides control criteria for pile stopping and a scientific basis for their design and construction.

Studies of nano-SiO2 and subsequent water curing on enhancing the frost resistance of autoclaved PHC pipe pile concrete

Autoclave curing will cause severe deterioration on the frost resistance of pre-stressed high-strength concrete (PHC) pipe pile. To clarify the frost resistance degradation mechanism of autoclaved PHC pipe pile concrete and obtain effective improvement measures, nano-SiO2 (NS) with cement replacement ratios of 0.5%, 1.0%, and 1.5% were adopted, and concrete specimens were fabricated and subjected to standard curing, autoclave curing, and autoclave curing + one week of subsequent water curing, respectively. Then, a rapid freeze-thaw cycle experiment was utilized to test their frost resistance. In addition, the micro-morphology and pore structure of different concrete were studied through scanning electron microscopy and nuclear magnetic resonance. The results indicate that the mechanisms of the degradation of autoclaved concrete in frost resistance are the increase of concrete porosity, harmful pore ratio, and concrete brittleness. Compared with standard curing, autoclave curing can result in 68.5% loss in the frost resistance of concrete. Through playing the filling and pozzolanic effects, NS can improve the compactness of autoclaved concrete and increase its frost resistance to a certain extent. Subsequent water curing can replenish water into concrete, promote the hydration of the residual unhydrated cementitious materials in concrete, enhance the compactness of concrete, and play a positive role in improving the frost resistance of concrete. The incorporation of 1.0% NS can enhance the frost resistance of autoclaved concrete by 66.6%, while the combination of 1.0% NS incorporation and one-week subsequent water curing can enhance the frost resistance by 89.2%. Exponential function can be used to simulate the frost resistance degradation of the autoclaved PHC pipe pile and predict its service life based on frost resistance.

Installation Effects and Behavior of a Driven Prestressed High-Strength Concrete Nodular Pile in Deep Saturated Soft Clay

This paper investigated the installation effects of a driven prestressed high-strength concrete (PHC) nodular pile in deep soft clay through full-scale tests, and the behavior of a driven PHC nodular pile is analyzed based on the field test results. The test results demonstrated that the driven PHC nodular pile installation process induced significant disturbance in the surrounding soil. The excess pore water pressures (Δu) that were induced by the installation of a driven PHC nodular pile were larger than the Δu that were induced by the installation of a driven PHC pipe pile. The driven PHC nodular pile installation caused significant Δu in the soil down to 2 m below the pile base, and the Δu became much smaller in the soil at 4 m below the pile base. The Δu dissipated slowly in the soft clay layers, and the Δu in the surficial soil layers dissipated faster than that in the deep soil layers. The nodules along the PHC nodular pile shaft could increase the pile shaft capacity. The measured shaft resistances of 350(400)-mm PHC nodular piles were 1.17–1.18 times the calculated shaft resistances of 350-mm PHC pipe piles in soft clay layers.

Durable life assessment of centrifugal stratified PHC piles in marine environment

This study proposes an analytical approach to assess the durable life of pre-stressed high-strength concrete (PHC) pipe piles exposed to the marine environment with consideration of centrifugal stratification and different end types. The durable life of the PHC pile is divided into two stages: the initiation stage for chloride penetration and the propagation stage for rust accumulation. To simulate the two stages, a two-layer composite cylinder diffusion model and a thick-walled ring mechanical model are developed based on the governing mechanisms. The proposed diffusion model is verified via comparisons with the numerical models with respect to chloride concentration under different stages. Then, extensive parametric studies based on the proposed method are performed to investigate the effects of end type, cover thickness, and steel bar diameter on the durable life of a PHC pipe pile. The results indicate that both increasing the cover thickness and using the closed-ended pile can significantly extend the durable life of a PHC pipe pile. Furthermore, the open-ended pile with a thinner mortar layer has a longer durable life, while the durable life of a closed-ended pile only slightly increases with a larger thickness of the mortar layer.

Static Load Test and Numerical Analysis of Influencing Factors of the Ultimate Bearing Capacity of PHC Pipe Piles in Multilayer Soil

Prestressed high-strength concrete (PHC) pipe piles have been widely used in engineering fields in recent years; however, the influencing factors of their ultimate bearing capacity (UBC) in multilayer soil need to be further studied. In this paper, a static load test (SLT) and numerical analysis are performed to obtain the load transfer and key UBC factors of pipe piles. The results show that the UBC of the test pile is mainly provided by the pile shaft resistance (PSR), but the pile tip resistance (PTR) cannot be ignored. Many factors can change the UBC of pipe piles, but their effects are different. The UBC of the pipe pile is linearly related to the friction coefficient and the outer-to-inner diameter ratio. Changes in the pile length make the UBC increase sharply. Low temperatures can produce freezing stress at the pile–soil interface. The effect of changing the Young modulus of pile tip soil is relatively small.

Application of Fiber Bragg Grating Sensing in Bidirectional Tests of Pile Foundations

Abstract The fiber Bragg grating (FBG) technique has emerged as a new strain monitoring technique in civil engineering applications. In this paper, based on the principle of the FBG technique and the bidirectional test method, FBG sensors and conventional vibrating wire strain gauges (VWSGs) were employed to monitor the strain variation law of a pile under different loads and analyze the relationship between the side resistance and pile-soil relative displacement of soil layers in bidirectional field testing of a large-diameter cast in situ pile. Four field bidirectional test cases of cast in situ piles, prestressed high-strength concrete (PHC) and steel pipe pile, and pile-base post-grouting pile are presented. The applicability and stability of the FBG sensing technique were verified by analyzing the side resistance distribution and bearing capacity. The results showed that FBG sensors can remove the influence because of residual force and the effect of temperature change and concrete expansion photosensitive material provides an improved sensitivity to the external environment compared with a VWSG. The strain and side resistance variation tendency of the cast in situ pile were consistent between the two kinds of sensors. The FBG sensing technique had high test accuracy in the four bidirectional O-cell field test cases of the cast in situ pile, PHC and steel pipe pile, and pile-base post-grouting pile. The pile-base post-grouting technique is an effective procedure that was implemented to increase the ultimate bearing capacity. The research results of this paper reveal a new strain monitoring technique for the bidirectional test method of pile foundations and represent a new test method for measuring the bearing capacity of PHC and steel pipe piles that has a remarkable application value in practical engineering.

Investigation on in-situ test of penetration characteristics of open and closed PHC pipe piles

To investigate the load transfer mechanism of open and closed Pre-stressed High-strength Concrete (PHC) piles jacked into layered soil, a full-scale in-situ test was conducted. In this test, the axial stress experienced by one open and two closed PHC pipe piles during jacking into layered soil was monitored using Fiber Bragg Grating (FBG) sensors mounted on pile shaft. The test results showed that (1) The jacking force on pile depended on the soil mechanical properties at the end of pile; (2) The variation of axial force on pile reflected that the compaction effect of soil for closed pile was larger than that for open pile; (3) At the beginning of penetration depth, the variation of shaft and end resistances on the open pile were different from those on the closed piles; (4) The variation of average shaft resistance relied on the mechanical properties of soil at the side of pile.

Field test of earth pressure at pile-soil interface by single pile penetration in silty soil and silty clay

Prestressed high-strength concrete (PHC) pipe pile with static press-in method is widely used in recent years. The earth pressure at the pile-soil interface caused by the process of pile jacking has an important influence on the jacked pile construction and even the bearing characteristics. Based on a construction project in Dongying, the change law of earth pressure at pile-soil interface caused by the penetration of PHC pipe pile is analyzed by monitoring the earth pressure at pile-soil interface during pile jacking, and the evolution characteristics of earth pressure at pile-soil interface in viscous soil foundation are revealed. The results show that the earth pressure at the pile-soil interface at different positions (h/B) caused by the penetration of PHC pipe pile gradually increases with time. In the process of pile jacking, the influence of pile jacking on the earth pressure at the pile-soil interface on the pile body and part that exceeds the relative distance of effective pile end (h/B) is weak. In the process of pile jacking, the earth pressure at the pile-soil interface is greatly affected by the relative height of the pile end (h/B), so it is necessary to consider the effect of the pile length to calculate the earth pressure at the pile-soil interface. The phenomenon of "lateral pressure degradation" exists with the increase of h/B in the earth pressure at the pile-soil interface. The research results have certain engineering guiding significance for construction and bearing capacity determination of jacked pile in viscous soil foundation.

Evaluation of Ultimate Bearing Capacity of Pre-Stressed High-Strength Concrete Pipe Pile Embedded in Saturated Sandy Soil Based on In-Situ Test

Estimation of ultimate bearing capacity (UBC) of pre-stressed high-strength concrete (PHC) pipe pile is critical for optimizing pile design and construction. In this study, a standard penetration test (SPT), static cone penetration test (CPT) and static load test (SLT) were carried out to assess, determine and compare the UBC of the PHC pipe pile embedded in saturated sandy layers at different depths. The UBC was calculated with three methods including the JGJ94-2008 method, Meyerhof method and Schmertmann method based on in-situ blow count (N) of SPT (SPT-N) which was higher than the values recommended in survey report regardless of pile length. The average UBC values calculated with cone-tip resistance and sleeve friction from CPTs was also higher than the value recommended in the survey report. Moreover, the actual UBC values directly obtained by load-displacement curves from SLTs were in line with the calculated values based on in-situ SPTs and CPTs, but approximately twice as high as the values recommended in the survey report regardless of pile length. For the SPT method, the application of bentonite mud in saturated sand layers is critical for the assessment of pile capacity in the survey phase, CPTs can provide reliable results regardless of soil characteristics and groundwater if the soil layer can be penetrated, and SLTs are necessary to accurately determine the UBC in complex stratum.

Experimental Research Based on the Optical Fiber Sensing Technology for a Jacked PHC Pipe Pile Penetration Process

The aim of this work is to explore the influence of the end resistance and shaft resistance regarding the mechanism for jacked pile penetration and the load-transfer rule during the penetration process. A full-scale field test was conducted in an actual project located in Dongying, Shandong Province, China. In this test, the axial strain experienced by two closed Prestressed High-strength Concrete (PHC) pipe piles during jacking into layered soil was monitored successfully using Fiber Bragg Grating (FBG) sensors mounted on the pile shaft. The experimental results show that FBG sensors have a good stability, strong antijamming performance, and can effectively monitor the pile stress. The variation law of the jacking force reflects the distribution of the soil layer, and the hardness of the soil layer at the pile end limits the pile force. When the pile end enters the silt layer from the clay layer, the jacking force and shaft resistance increase by 2.5 and 1.7, respectively. The shaft resistance accounted for 44.99% of the jacking force. The end resistance is affected by the mechanical properties of soil, and the end resistance of the silt layer is approximately twice that of the clay layer. The end resistance of the silt layer accounted for 59.84% of the jacking force. When the pile end enters the soft soil layer from the hard soil layer, the impact of the pile driving speed and the tangential force on the surface of the pile body must both be considered. During the pile penetration process, as the penetration depth increases, the radial stress on the pile side at a given depth is gradually released, while the shaft resistance at the pile side degrades significantly.

Field Test of Excess Pore Water Pressure at Pile-Soil Interface Caused by PHC Pipe Pile Penetration Based on Silicon Piezoresistive Sensor.

Prestressed high-strength concrete (PHC) pipe pile with the static press-in method has been widely used in recent years. The generation and dissipation of excess pore water pressure at the pile–soil interface during pile jacking have an important influence on the pile’s mechanical characteristics and bearing capacity. In addition, this can cause uncontrolled concrete damage. Monitoring the change in excess pore water pressure at the pile–soil interface during pile jacking is a plan that many researchers hope to implement. In this paper, field tests of two full-footjacked piles were carried out in a viscous soil foundation, the laws of generation and dissipation of excess pore water pressure at the pile–soil interface during pile jacking were monitored in real time, and the laws of variation in excess pore water pressure at the pile–soil interface with the burial depth and time were analyzed. As can be seen from the test results, the excess pore water pressure at the pile–soil interface increased to the peak and then began to decline, but the excess pore water pressure after the decline was still relatively large. Test pile S1 decreased from 201.4 to 86.3 kPa, while test pile S2 decreased from 374.1 to 114.3 kPa after pile jacking. The excess pore water pressure at the pile–soil interface rose first at the initial stage of consolidation and dissipated only after the hydraulic gradient between the pile–soil interface and the soil surrounding the pile disappeared. The dissipation degree of excess pore water pressure reached about 75–85%. The excess pore water pressure at the pile–soil interface increased with the increase in buried depth and finally tended to stabilize.

Impact of Marine Chloride Ion Erosion Environment on the Durability of Deep Sea Pile Foundation

Yan, Y.; Tian, T., and Wang, B., 2019. Impact of marine chloride ion erosion environment on the durability of deep sea pile foundation. In: Li, L.; Wan, X., and Huang, X. (eds.), Recent Developments in Practices and Research on Coastal Regions: Transportation, Environment and Economy. Journal of Coastal Research, Special Issue No. 98, pp. 6–9. Coconut Creek (Florida), ISSN 0749-0208.Subject to the chloride-induced corrosion, pipe pile foundations will suffer losses of the cross-sectional area of the steel bar, the bond strength between the steel bar and the concrete, as well as its bearing capacity. Even worse, it will malfunction. It is of great engineering significance to explore the corrosion initiation time and evaluate the service life of steel bars in pipe pile foundations under a marine environment. Based on Fick's law, this paper investigates the bilateral diffusion of chloride ions in pipe pile foundations in coastal areas and analyzes how the chloride ion diffusion effect is subjected to some key parameters such as bilateral erosion from chloride ions, mortar and concrete stratification, and temperature. In the end, the service life of prestressed high-strength concrete (PHC) pipe piles withstanding the bilateral diffusion of chloride ions is discussed. The findings show that when the temperature difference between the inner and outer walls of the pipe pile foundations is greater than 15°C, the wall temperature correction factor is quite different. It should be corrected according to the actual service conditions of the pipe pile foundations. Based on the hollow structure of PHC pipe piles, one should consider the simultaneous diffusion of chloride ions from the inner and outer walls and the centrifugal stratification of the pipe pile foundations when designing its service life. The mortar layer thickness and the ambient temperature are dominant factors that the service life of PHC pipe piles will be subject to. If the service year of the pipe pile foundation is 50 years, given the impact of the mortar layer, the thickness of the pipe pile foundation should be greater than 95 mm, and the mortar layer should be less than 10 mm; given the temperature effect, the pipe wall thickness should be greater than 100 mm. If the service year is 100 years, given the impact of the mortar layer, the wall thickness should be greater than 145 mm, and the mortar layer should be less than 25 mm; given the temperature effect, the wall thickness should be greater than 150 mm.

Durability and microstructure of steam cured and autoclaved PHC pipe piles

Effects of two different curing regimes (steam curing and autoclaved curing) on durability of pre-stressed high-strength concrete (PHC) pipe piles with fly ash (FA) had been investigated. The chloride penetration, salt and frost resistance performances of PHC pipe piles with these two curing regimes were tested. The results showed that the chloride ion permeability coefficient of steam cured sample at 85 °C for 4.5 h was decreased by 97.13% compared with that of autoclaved one, these steam cured sample could stand 150 times of salts (5% Na2SO4 + 3.5% NaCl solution) corrosion tests and 550 times freeze-thaw tests. The pore structural and micro-cracking analysis of samples with three water to binder ratios (0.21, 0.23, 0.25) revealed that the mean total porosity values of these steam cured sample were about 5%, which was less than half of that of autoclaved samples. The dipping dyeing test showed that the mean micro-cracks width, length and the density of the steam cured samples were less than that of the autoclaved samples. The results supported that by optimizing the mix ratio and curing regime the PHC pipe piles could be prepared with satisfied mechanical and durability performances. So a feasible low-carbon manufacturing technology for PHC pipe piles was provided.

Analysis of Influence of Sand Parameters on Seismic Performance of PHC Piles

In order to study the effect of sand parameters on the seismic behavior of prestressed high-strength concrete (PHC) pipe piles, using the general finite element software ABAQUS6.12, by applying horizontal reciprocating load on the top of the pile, the influence of sand parameters on the seismic behavior of PHC piles under horizontal load is studied. The results show that increasing the relative density of sand increases the degree of hysteresis of PHC pipe pile hysteresis curve and reduces the cumulative hysteresis energy of PHC pipe piles; Increasing the internal friction angle of the sand increases the hysteresis loop area of the PHC pipe pile, and the cumulative hysteresis energy consumption increases; Increasing the initial modulus of sand soil resistance makes the PHC pipe pile stagnation loop shrinkage, and the cumulative hysteresis energy consumption decreases slightly. Increasing the relative density of sand, internal friction angle and initial modulus of soil resistance can increase the overall stiffness of the pile-soil system, increase the horizontal ultimate bearing capacity of PHC piles and reduce the ultimate displacement of PHC piles.

Field Performance of Open-Ended Prestressed High-Strength Concrete Pipe Piles Jacked into Clay.

The behavior of open-ended pipe piles is different from that of closed-ended pipe piles due to the soil plugging effect. In this study, a series of field tests were conducted to investigate the behavior of open-ended prestressed high-strength concrete (PHC) pipe piles installed into clay. Two open-ended PHC pipe piles were instrumented with Fiber Bragg Grating (FBG) sensors and jacked into clay for subsequent static loading tests. Soil plug length of the test piles was continuously measured during installation, allowing for calculation of the incremental filling ratio. The recorded data in static loading test were reported and analyzed. The distribution of residual forces after installation and the effect on the bearing capacity were also discussed in detail. The test piles were observed to be in partially plugged condition during installation. The measured ultimate shaft resistance and total resistance of the test piles were 639 and 1180 kN, respectively. The residual forces locked in the test piles after installation significantly affected the evaluation of the axial forces, and thus the shaft and end resistances. It tended to underestimate the end resistances and overestimate the shaft resistances if the residual forces were not considered in the loading test. However, the residual forces did not affect the total bearing capacity of open-ended PHC pipe piles in this study.

Pseudo-static low cycle test on the mechanical behavior of PHC pipe piles with consideration of soil-pile interaction

Pre-stressed high-strength concrete (PHC) pipe piles have been widely used in the pile foundations of buildings and bridges which are usually designed elastic based on the capacity design principle. However, when the PHC pipe pile comes to the foundations of Integral Abutment Jointless Bridges (IAJBs), limited ductility might apply in order to accommodate the relatively large deformation demand under the effect of temperature fluctuations or earthquake. The conventional design methods for PHC pipe piles remain in doubt. This paper focuses on low cycle pseudo-static tests on 4 PHC pipe-pile models with various pre-stress levels to gain insight into their mechanical behaviors with consideration of soil-pile interaction. Medium sand was employed in the tests. The details of the experiments are introduced, including design of the models, instrumentation and loading scheme. The testing results indicate that the damages of the PHC pipe piles are mainly concentrated at 4D to 8D of embedded depths. Moreover, the pre-stress level and reinforcement ratio have a significant influence on the failure mode of PHC pipe piles, especially on the distribution of internal force and moment along piles. It is found that the interaction effect of pile-soil strengthens with the pre-stress level which is beneficial to the seismic performance. Furthermore, the backbone of the PHC pipe piles model has four stages: elastic, elastic-plastic, plastic hardening, and failure. It is concluded that PHC pipe piles perform favorably plastic and ductile behavior, and their failure modes are flexural (bending) not brittle (shear). Finally, the PHC pipe pile has an appreciable energy dissipation and deformation capacity, and hence can be used for pile foundations in IAJBs.