灌注桩中钢筋笼为铁磁性物质,在地磁场中受到磁化而产生磁场强度,使钢筋笼附近的磁场强度发生变化。根据井中磁测法的探测原理,得到钢筋笼的磁异常解析式,分析了钢筋笼的外部磁场特征,并通过模型桩测试成果加以验证,最后利用实测磁场特征来确定工程桩中钢筋笼的长度。理论分析和工程应用均表明,采用磁测井法检测灌注桩内钢筋笼长度是有效而可靠的。 Reinforcing cage in bored pile is a ferromagnetic material, which is magnetized in the geomagnetic field to generate magnetic field strength, so that the magnetic field intensity near the steel cage changes. According to the principle of magnetic detection in the well, the analytical solution of the magnetic anomaly of the reinforced cage is obtained. The external magnetic field characteristics of the reinforced cage are analyzed and verified by the model pile test results. Finally, the measured magnetic field characteristics are used to determine the length of the reinforced cage . Both theoretical analysis and engineering application show that it is effective and reliable to measure the length of reinforcement cage in cast-in-situ pile by magnetic logging.