Experiment and Numerical Study on Deformation Measurement of Cast-in-Place Concrete Large-Diameter Pipe Pile Using Optical Frequency Domain Reflectometer Technology

The Cast-in-place concrete large-diameter pipe (PCC) pile has been used as the foundation reinforcement and embankment in China due to its low cost and high bearing capacity. The deformation of PCC pile under different vertical loads is very important for the application of engineering. In order to study the deformation characteristics of PCC pile, a small-scale model test was carried out. The new distributed measuring technology, named Optical Frequency Domain Reflectometer (OFDR), was applied to measure the strain on the PCC pile. A single mode fiber (SMF) was used, and the methods of layout, packaging and protection of optical fiber are introduced in detail. The obtained data was dealt with by wavelet transform, and the strain curves were analyzed based on the experiments. The finite element (FE) analysis model was established by COMSOL Multiphysics, and the numerical results compared with the experiment results. It showed that the optical fiber sensor can measure the strain of PCC pile, and that the deformation of PCC pile can be successfully obtained by OFDR technology. The strain of the pile decreases with depth and increases with loading. The measured result agrees well with numerical simulation result. The potential application of OFDR technology to PCC pile in situ and PCC energy pile is discussed.

First application of cast-in-place concrete large-diameter pipe (PCC) pile-reinforced railway foundation: a field study

Cast-in-place concrete large-diameter pipe (PCC) piles have been widely used in highway construction for foundation reinforcement, where soft ground was encountered, due to their fast on-site construction and high capacity, hence economics. This paper reports the performance of their first application in high-speed railway foundation reinforcement on soft soil ground. To satisfy the strict settlement requirement for railway design, PCC piles with large diameters (D = 1 m), thick pile wall thicknesses (t = 0.15 m), and close spacing (s = 2.5 m) were constructed. The foundation performance has been monitored by measuring in situ foundation settlement, excess pore pressure in soil, lateral displacement of soil, and tension in the geogrid during and after embankment construction. The measurements of this project have been compared with that of a previous project when PCC piles were used. It is found that the PCC pile arrangement in this project has performed as predicted and fulfilled the strict settlement requirement set by the Chinese design guidelines.

Elasto-Plasticity Solution on Bearing Characteristic of Cast-in-Place Concrete Pipe Pile with Large Diameter in Layered Soil under Lateral Load

Aimed at problems lying in the exiting methods for calculation of laterally loaded piles installed in layered soils, the elasto-plasticity solution of cast-in-place concrete pipe pile with large diameter (PCC pile) in layered soil under lateral load based two-parameter foundation model and unity limiting force profile, deduced the finite difference solution based unity limiting force profile(LFP), established the calculation program of the displacement and internal force of pile. It was shown that the calculated pile moment and pile displacement coincided very well by computation and comparison of model test and FEM, verified the method’s correction. Meanwhile, the method was more precise and efficient than the existing conversion methods of subgrade modulus. Therefore, it could be useful for the design and analysis of PCC pile under lateral load.