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

Abstract

<jats:p>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.</jats:p>

The Effects and Vertical Bearing Capacity of Two Jacked Model Piles in Sand

“…Meanwhile, the radial stress of Pile #1 was lower than that of Pile #2, and the radial stress of the pile was mainly affected by the pile's length or depth. In the case of Pile #1, the radial stress of the pile increased by 35% (the depth of 11 D) and 270% (the depth of 13 D) for every 2 D increase after the depth of 9 D; however, at the same depth, the radial stress of the pile decreased with the increasing pile length- [4] suggests that this was due to the "friction fatigue effect" between the pile and soil during the installation of the pile; the continuous penetration process of the pile caused continuous disturbance of the soil around the pile, resulting in the release of the soil stress around the pile and causing the relaxation of the soil around the pile, so the pile-soil friction during the pile-sinking process is one of the factors causing the reduction in the radial stress of the pile. Meanwhile, the radial stress of the pile decreased slightly and was only 26% at the depth of 0~4 D, while the decrease was larger with a maximum of 59% at the depth of 4~8 D, which was due to the relatively small value of the radial stress of the pile that leads to the inconspicuous decrease, and the difference is gradually highlighted as the value of the radial stress of the pile increased.…”

“…Most studies show that the jacking pile's pressure increases nonlinearly with the increasing depth [1,2]. The pile end resistance's change with the depth is similar to that of jacking pile pressure, and the pile end's resistance accounts for a large proportion of the pile's force [3,4]. There is a critical depth such that the pile end's resistance reaches a critical value [5].…”