Model Test of Jacked Pile Penetration Process Considering Influence of Pile Diameter

In order to investigate the influence of different diameters on pile end resistance, pile side resistance, pile axial force and pile force transmission law of jacked pile penetration, two pairs of embedded sensitized microfiber grating sensors were installed by slotting the pile body. The pile-jacking process of static-pressing viscous foundation soil with different diameters of closed-tube model piles was successfully monitored. The test results show that the pile pressure, pile end resistance and pile side resistance of the two test piles increase linearly with the increase of pile depth. When the pile jacks, the final pressure of the test pile TP1 is higher than that of the test pile. TP2 is 31% higher, pile end resistance is 18% higher, and total side resistance is 57% higher. The results show that increasing the pile diameter can significantly increase the pile side resistance; under different penetration depths, the pile side resistance is from top to end. Continuously exerted, the axial force of the pile body decreases with the depth of the pile and the slope of the distribution curve of the axial forcegradually decreases. At the maximum penetration depth, the axial force of the pile TP1 is 18% larger than that of the test pile TP2; As the depth increases, the unit side resistance at the same penetration depth gradually decreases, that is, the side resistance has a “degradation effect”; at the end of the pile jacking, the percentage of the pile end resistance to the pile force exceeds 50%, that is, the pile end resistance bears most of the load. This research can be used as a reference for the study of pile driving mechanism in clayey and layered clayey soils.

Grain-scale DEM study of open-ended pipe pile penetration in granular soils

Open-Ended Pipe Piles (OEPP) are particularly popular in offshore engineering. An important feature of the installation of these piles is the rate with which soil enters the pile from the bottom, and its interaction with the internal pile shaft. The response of OEPP crucially depends on the occurrence of soil plugging, which can make the behavior of an OEPP similar to a pile of solid cross section. Plugging is generally attributed to arching effects in the soil; therefore, understanding this phenomenon requires an investigation at the grain scale. This is precisely the objective of this study, where the Distinct Element Method (DEM) is used to study the installation of an Open-Ended Pipe Pile in a Virtual Calibration Chamber comprising 128000 grains, under constant horizontal stress. Despite the relatively small number of particles, this numerical model is found to be able to reproduce several aspects of the mechanisms actually observed in thefield. The results are compared to those obtained from actual experiments of miniature pile penetration tests. Stress and strainfields that develop in the soil inside and outside the pile provide interesting data and shed light on the mechanisms at play during OEPP installation, especially as for the influence of grains interlocking.

Experimental study and theoretical analysis on impact characteristics of single pile

The impact characteristics of a single pile are the theoretical basis of the high-strain detection technology of piles and pile driving. Firstly, a series of pile model experiments are conducted to study the characteristics of single pile penetration, axial force and friction of the pile under impact loads of different rammer loads and falling distances. Then, the dynamic model of a single pile under impact load under the condition of pile-soil slippage was established by using the elastodynamic method, and the analytical solution of the pile axial force was obtained. The results show that the theoretical solution is in good agreement with the model test results. This shows that the completely bonded model without considering slippage overestimates the frictional resistance between the pile and soil, and the pile-soil slippage model can better simulate the impact of a single pile in sand.

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

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.