Abstract
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.
Highlights
A Prestressed High-strength Concrete (PHC) pipe pile is a hollow cylindrical precast concrete member produced by pretension prestressing, centrifugal techniques, and high temperature curing [1,2,3,4]
PHC pipe piles are widely used in foundation works in civil, municipal, and other projects in China due to the advantages of a high bearing capacity, high construction efficiency, and reliable quality [5,6,7,8]. e hydraulic jacking method is a common technique for pile penetration that has several advantages such as being vibration-free and noise-free during construction [9,10,11,12]. is method is generally used to press a PHC pipe pile into the site soil
To investigate the capacity properties of closed PHC pipe piles during penetration into a layered stratum, a full-scale test was conduct based on an actual project located in Shandong province, China. e low-temperature sensitive, Fiber Bragg Grating (FBG) strain sensors, and FBG temperature sensors were installed in the shallow grooves along opposite sides of the PHC pipe piles. us, the strain of the PHC pipe piles can be measured to avoid the effects of temperature under hydraulic driving. us, the axial force, end resistance, shaft resistance, and unit shaft resistance of the PHC pipe pile under hydraulic driving can be calculated. e research results can provide reference and guidance for jacked pile engineering in a cold region
Summary
A Prestressed High-strength Concrete (PHC) pipe pile is a hollow cylindrical precast concrete member produced by pretension prestressing, centrifugal techniques, and high temperature curing [1,2,3,4]. To further improve the accuracy and resolution of the tests, Fiber Bragg Grating (FBG) sensors have been used to Advances in Civil Engineering monitor the stress and strain of pile foundations. Lee et al [29] measured the strain of a PHC pipe pile during static load testing based on the FBG strain sensors and strain gauges. Liu et al [33] monitored the end and shaft resistances of an open-ended PHC pipe pile using FBG strain sensors. To improve the monitoring accuracy of FBG strain sensors in pile tests, the temperature should be compensated for, especially in cold regions. Us, the strain of the PHC pipe piles can be measured to avoid the effects of temperature under hydraulic driving. Installation of PHC Pipe Piles with FBG Sensors for Field Monitoring. The pile length was used as the final pressure control standard. e test data were collected using the FS 2200RMRack-Mountable Bragg Meter demodulator produced by Portugal, which directly collected the wavelength difference from the center wavelength of the fiber grating
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