Abstract
The small deformation of the model pile in a pile jacking test makes its accurate measurement very difficult. Based on the installation method of clamping at both ends, a sensitized miniature fiber Bragg grating (FBG) strain sensor was developed to measure the pile strain of small-size model piles. This study investigated the working principle of the sensitized miniature FBG sensor and analyzed the strain transfer characteristics of the sensor by calibration test. The lateral resistance and the earth plug resistance of the model pile were measured accurately by the grooves embedded in the outer tube of the double-wall opening model pile and the sensors directly pasted on the surface of the inner tube. The results of this study show that the sensitized miniature FBG strain sensor has the advantages of high sensitivity, strong interference resistance, and high test accuracy. The FBG strain sensor was completely fixed on the pile by clamping supports at both ends, and the strain measured using the FBG strain sensor was found to be consistent with the pile deformation.
Highlights
In the process of pile jacking, the pile body is subjected to complex forces, in which the pile end breaking the soil faces the resistance of the pile end, and the outer wall of the pile body produces sliding friction with the soil, i.e., the lateral resistance of the pile and the wall of the open-pipe pile body exert resistance to the soil plug because of the earth plug effect, i.e., the resistance of the pile inside [1]
The problem of pile jacking has been investigated in detail through indoor model tests, in which most model piles are made of steel or aluminum pipes [2,3,4,5,6]
According to the numerical calculation results, in the double-wall opening model pile, miniature fiber Bragg grating (FBG) strain sensors with sensitization were installed at 20 mm from the outer pipe to the pile end and 80 mm from the pile top to measure the changes in the pile end resistance and pile pressure during pile jacking process
Summary
In the process of pile jacking, the pile body is subjected to complex forces, in which the pile end breaking the soil faces the resistance of the pile end, and the outer wall of the pile body produces sliding friction with the soil, i.e., the lateral resistance of the pile and the wall of the open-pipe pile body exert resistance to the soil plug because of the earth plug effect, i.e., the resistance of the pile inside [1].An indoor model test is the most direct method to study the mechanical properties of penetration of the piles. In order to avoid the boundary effect of the model test and satisfy the geometric similarity ratio of the model pile and the engineering pile, the diameter and length of the model pile are both kept small. The model piles in the centrifuge designed by Nicola et al [7] and Klotz et al [8] are all 16 mm in diameter, and the pile lengths are 350 and 375 mm, respectively. Zhang et al [10] designed instrumented model piles with the inner and outer diameters of 12.7 and 16.0 mm, respectively, and a pile length of 600 mm. The stress environment of the model pile during the pile jacking process is complicated, making the strain measurement of the model pile very difficult
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
