Application of Integrated Geophysical Prospecting Method to Quality Evaluation of Existing Cast-in-place Pile

The pile length and integrity testing of existing cast-in-place piles are often difficult to effectively verify due to limited site conditions. To enhance evaluation accuracy, this paper employs a comprehensive geophysical exploration method combining magnetic logging, side-hole transmission, and cross-hole elastic wave CT to systematically investigate the target foundation piles: magnetic logging is used to detect the length of the reinforcement cage, side-hole transmission is used to determine the pile length and defects in the pile body, and cross-hole elastic wave CT is used to identify defects in the pile body and the condition of the bearing stratum, thereby providing an overall assessment of the construction quality of the pile foundation and providing basis and suggestions for subsequent treatment. The detection results show that the combination of the above methods can clearly delineate the interface between the overburden soil layer and the bedrock, which is basically consistent with the drilling exposure; the combination of magnetic logging and side-hole transmission can effectively infer the pile length; the combination of cross-hole elastic wave CT and side-hole transmission can accurately determine the range of defects in the pile body; and the combination of cross-hole elastic wave CT and pile length results can reasonably infer the condition of the pile tip bearing stratum. The comprehensive geophysical exploration method has the advantages of low cost, high efficiency, and multi-method complementary verification, and is currently a reliable technical approach for evaluating the quality of existing cast-in-place piles.