Parameter Preferences for Length Detection of Reinforcement Cage in Bored Pile

Reinforcement cage length has a significant impact on the bearing capacity of bored piles. Accurate measurement of the cage length provides an important guideline for judging pile quality. Currently, the electric method has been widely used in detecting reinforcement cage length. However, the precision of detection results requires further improvements. This paper presents an electric potential difference method for length detection based on theoretical analyses and formula derivations. Against the numerical calculation it can be observed that detection accuracy increased along with increases in the actual skeleton length and decrease of the pile-to-borehole distance, electrode spacing, and moving step size of electrodes. Parameter preferences of length detection were recommended as follows: (1) the electric potential difference method was recommended to complete the detection when the designed length of the pile was more than 8 m; (2) the pile-to-borehole distance was suggested to be less than one-fifth of the designed cage length; (3) the electrode spacing should be no more than a hundredth of the designed cage length; (4) the moving step size was limited to less than one-tenth of the designed skeleton length, and the length was an integral multiple of the step size. Moreover, the results and recommendations were verified by physical model experiments and engineering practices.