Pre-stressed Concrete Pipe Piles Research Articles

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.

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.

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.

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.