Pre-stressed Concrete Pipe 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.

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.

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.

Full-scale experimental research on the bending fatigue performance of post-tensioned prestressed concrete pipe piles

Post-tensioned prestressed concrete pipe piles (large cylinder piles) have been widely used in port and bridge engineering because they are economical and deliver excellent performance, and thus, have potential for use in offshore engineering. However, limited research has been devoted to the bending fatigue of large cylinder piles, which is essential for offshore engineering design. This study evaluated the bending fatigue of large cylinder piles by performing a series of full-scale bending fatigue tests on three specimens (L = 12 m, D = 1.2 m) and numerically analyzing the static cracking patterns in them. The static performance of large cylinder piles, including the bending moment of static cracking (Mcr) and its patterns, was analyzed by using a validated finite element model. Three-point bending fatigue tests with cyclic loading under a constant amplitude (stress ratio R = 0.4, peak fatigue load = 37.72%–80.00% Mcr) were then conducted to examine the development of mid-span displacement and stiffness degradation in the specimens. A critical damage factor (Dcr), which uses the cracking of concrete as the indicator of termination of the test, and a modified approach to prediction were then proposed and applied, based on findings of the fatigue test and past literature, to predict the number of cycles that it took for the large cylinder piles to crack. Finally, bi-linear S–N curves were plotted by considering the effective prestress according to the experimental and estimated data. The results here provide a theoretical basis for the fatigue-based design and application of large cylinder piles.

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.

Field investigation into the performance of pipe pile in soft clay under static and cyclic axial loads

We performed a field investigation into the effective stress, the shaft friction at the pile–soil interface, and the pile-end base resistance of a 29.5 m long prestressed concrete pipe pile in soft clay under static and cyclic loadings (50 000 cycles). Our results indicate that under low-level cyclic loading (CLR ≤ 0.2, where CLR is the ratio of cyclic load amplitude to the ultimate capacity), the pore water pressure at the pile–soil interface initially accumulates with the number of cycles, followed by gradual dissipation after reaching its maximum value. The effective stress also initially decreases and then increases. The shaft friction increases after cyclic loading. Owing to axial load redistribution, the base resistance decreases with the number of cycles. When the pile is subjected to high-level cyclic loading (CLR ≥ 0.5), the pore water pressure at the pile–soil interface keeps accumulating while the effective stress continues to decrease, leading to the degradation of shaft friction. The base resistance increases as a result of axial load redistribution. In particular, we analyzed the effects of the static load level and the cyclic load level on the changes shaft friction.

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.

Reinforcement Effect of Inclined Prestressed Concrete Pipe Piles on an Inclined Soft Foundation

The embankment slope is vulnerable to slip and collapse, when prestressed concrete pipe (PCP) piles are used to reinforce the inclined soft foundation to bear the load of the embankment. Accordingly, this study puts forward new programs for strengthening embankment foundation with inclined, rather than vertical, PCP piles. Based on an actual engineering accident with embankment slope collapse, this study establishes a finite element model, accompanied by analysis of engineering characteristics and reinforcement effects of the foundation. The main conclusions are drawn as follows: (1) when a pile‐supported foundation is used to strengthen the inclined soft foundation, PCP piles in the lower part of the embankment are subjected to bending moments, with their maximum value appearing in the upper part of the PCP pile at the embankment slope foot. During the embankment filling, the maximum pile bending moment may reach the ultimate bending load, resulting in bending failure accompanied with large lateral displacement and even slope collapse. The maximum horizontal displacement of the foundation is located at the foot of the embankment slope. (2) Reinforcement using inclined PCP piles contributes to smaller maximum pile body bending moments than that using vertical PCP piles and loading berms, and such contribution is enhanced when the inclination angle of PCP piles in the lower part of the slope gets larger. Therefore, inclined PCP piles with high angles are optimum in improving the overall stability of the foundation. (3) Compared with vertical PCP piles, inclined PCP piles contribute to smaller horizontal displacement and vertical settlement in foundation reinforcement, which means better reinforcement effects. Moreover, as the inclination angle of PCP piles increases, the maximum displacement decreases rapidly, associated with greatly enhanced lateral stability.

Engineering Characteristics and Reinforcement Program of Inclined Pre-stressed Concrete Pipe Piles

When it comes to the deep soft soil foundation, improper construction, preloading, and excavation may result in the inclination of the pre-stressed concrete pipe (PCP) piles. Lack of understanding on deformation characteristics may lead to inaccurate reinforcement plan, thereby causing new engineering accidents. This study analyzes an engineering accident induced by the pile inclination, based on which the finite element method model is built. Deformation characteristics of the foundation incorporating inclined PCP piles are investigated, and the reinforcement program involving placement of the pile with opposite inclination is proposed and compared with the conventional reinforcement program using vertical piles. Findings of this study are two-folds: 1) A critical inclination angle affecting the vertical settlement exists, below which the pile inclination has limited effects upon the vertical load bearing capacity of the foundation. 2) The vertical subsidence, the lateral displacement and the bending moment of the reinforcement program based on the reversely inclined pile are all decreased, which helps bear the overburden load and improve stability. In the process of engineering accident treatment, the bearing capacity of PCP piles with small inclination angles can be first reduced according to their inclination angles, followed by judgement that whether these PCP piles meet the requirements on bearing capacity. The PCP piles with large inclination angles must be strengthened, and the reverse inclined PCP piles are recommended.

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.

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.

Reply to the discussion by Zhang et al. on “Field study of residual forces developed in pre-stressed high-strength concrete (PHC) pipe piles”

Reply to the discussion by Zhang et al. on “Field study of residual forces developed in pre-stressed high-strength concrete (PHC) pipe piles”

Discussion of “Field study of residual forces developed in pre-stressed high-strength concrete (PHC) pipe piles”

Discussion of “Field study of residual forces developed in pre-stressed high-strength concrete (PHC) pipe piles”

Corrigendum: Field study of residual forces developed in pre-stressed high-strength concrete (PHC) pipe piles

<i>Corrigendum:</i> Field study of residual forces developed in pre-stressed high-strength concrete (PHC) pipe piles

Field study of residual forces developed in pre-stressed high-strength concrete (PHC) pipe piles

A large-scale field testing program for the study of residual forces in pre-stressed high-strength concrete (PHC) pipe piles is presented in this paper. Five open-ended PHC pipe piles with 13 or 18 m in embedded length were installed and used for static loading tests at a building site in Hangzhou, China. All the piles were instrumented with fiber Bragg grating (FBG) strain gauges. The residual forces in these piles were recorded during and after installation. The measured load transfer data along a pile during the static loading tests are reported. The effect of the residual force on the interpretation of the load transfer behavior is discussed. The field data show that residual force along the installed pile increases approximately exponentially to the neutral plane and then reduces towards the toe. The residual force decreases with time to a stable value after pile jacking due to the secondary interaction between the pile and the disturbed soil around the pile and other factors. The large residual forces along the PHC pipe piles significantly affect the evaluation of the pile load distributions, and thus the shaft and toe resistances. The conventional bearing capacity theory tends to overestimate the shaft resistance at positions above the neutral plane and underestimate the shaft resistance at positions below the neutral plane, and the toe resistance for an open-ended PHC pipe piles founded in stratified soils.

Field tests and finite element modeling of a Prestressed Concrete Pipe pile-composite foundation

The Prestressed Concrete Pipe (PCP) pile-composite foundation was initially employed in the foundation of a culvert in the ancient Yellow River of China. To analyze the reinforcement effect of the foundation, a composite foundation composed of PCP piles was investigated with field tests and numerical simulations. A static load test was conducted to investigate the stress and deformation of the PCP pile-composite foundation, and a finite element model under three-dimensional (3D) axisymmetric conditions was developed to simulate the stress and deformation of the foundation. The Finite Element (FE) model used a nonlinear constitutive model for the soil, cushion and pile-soil interface. The results of the numerical simulations correspond with the load sharing, stress and displacement results of the static load test and indicate that the soil stress is primarily compressive. The cushion reduces the difference in settlement between the middle region and the side region of the bearing plate and increases the bearing capacity of the PCP pile-composite foundation. The stress of the pile significantly varies in the upper 1 m. The pile-soil load-sharing ratio increases with an increase in external load. This paper is expected to be useful for scientific research and efficient applications of PCP pilecomposite foundations.

Discussion about the Application of Pre-Stressed Concrete Pipe Pile

In this paper, based on the author of many years engineering practice, analyzes and discusses the common problem in the application of high strength static pressure concrete pipe pile. For the reasonable application of pipe pile in Changchun area provide advices and references.

The Applied Analysis of Static Pressure Prestressed Pipe Pile in Cohesive Soil

The article analysis and summary how to control the final pressure value of site operation by taking project in Changchun as an example when the cohesive soil layer use static prestressed concrete pipe pile foundation, putting forward the methods and suggestions of controlling final pressure value.

Termination criteria for jacked precast high-strength prestressed concrete pipe piles

Precast high-strength prestressed concrete pipe piles installed by the jacking method have received wide use as deep foundations in China. Adoption of appropriate termination criteria during installation is the key issue to ensure design capacity or avoid conservative design for jacked piles. A database including 1228 field load tests on jacked concrete pipe piles is collected in this study to establish empirical correlations between the final jacking force and the ultimate capacity. Using the pile slenderness ratio as the fundamental parameter, a total of 14 correlations are derived to apply for various categories of soil conditions. Among them, the ratio of pile capacity to jacking force for piles in stiff clay and firm clay exhibits the greatest magnitude and trend of increase with increasing pile slenderness ratio. Moreover, two jacked concrete pipe piles in silty clay are instrumented and load-tested as an independent case to examine the consistency of the proposed correlations. The two test piles are installed in accordance with a double-control termination criterion that involves the requirements of both final penetration and final jacking force. The load transfer behaviour of the piles has revealed that their performances satisfy all the design requirements.