Application of the Combination of High-Density Electrolysis Method and Drilling Method in Bridge Karst Cave Investigation

In the design and construction of expressway bridges, over-reliance on drilling investigation often suffers from the limitation of “using points to represent the whole area”, making it difficult to fully reveal the spatial structural characteristics of the pile foundation bearing stratum. This discrepancy frequently leads to inconsistencies between actual geological conditions and survey data during construction. Taking the Leicun Bridge of the Guangzhou-Lianzhou Expressway as an example, no karst development was identified in the detailed survey stage of this project; however, a large karst cave was discovered during construction. To clarify the distribution and scale of the karst cave, this study adopted a comprehensive investigation method combining “3D surveying + high-density electrical method + drilling verification”. Through the high-density electrical method, 9,384 measurement points were collected along 13 survey lines (with a total length of 4,435 meters). By integrating RES2DINV inversion and Surfer planar mapping, the identification and interpretation of low-resistivity anomaly areas were realized. Subsequent drilling verification finally confirmed that the karst cave has a length of approximately 120 meters, a width of approximately 25 meters, a height of approximately 11 meters, and a total volume of about 1.68×10⁴ cubic meters. The results show that the high-density electrical method can effectively detect large karst caves that cannot be found by drilling alone, and its combination with drilling significantly improves the accuracy and reliability of geological investigation. This study provides a scientific basis for the design modification and treatment of pile foundations in karst cave areas, and has popularization value for the investigation of bridges in similar karst regions.