Experimental Study on Signal Characteristics of Pile Foundation Length Detection Based on Magnetic Field Model

The length of steel reinforcement cage is an important factor indicator that affects the pull-out, bending, seismic mechanical performance, and safety and stability of cast-in-place piles, and its length detection is crucial. As a typical ferromagnetic material, steel cage will exhibit a significant change in the magnetic field near the cage after being magnetized by the geomagnetic field environment. Based on the abnormal magnetization characteristics and magnetic charge theory, this paper constructs a magnetic field detection model for the length of steel cage using the magnetic well method. The test results show that the abnormal characteristics of the vertical component and gradient of the magnetic field in the steel cage are closely related to the position of the bottom of the steel cage, and can be used as a basis for determining the length of the steel cage. The parametric analysis of the magnetic field model of the reinforcing cage concluded that the spacing of the probe hole pile holes has a large influence on the anomalous characteristics of the tested magnetic field. When conducting engineering inspections, it is necessary to ensure that the distance between the pile holes is within 1.0 m. By analyzing the magnetic field model of the steel cage and verifying it through engineering pile tests, the principle of magnetic anomaly characteristics and the working mechanism of the magnetic well method are revealed. This paper constructs an analytical model for the magnetic field of steel cage through theoretical analysis and engineering pile test research, providing theoretical reference for the application of length detection technology for pile foundation steel cage.