Application of Ultra-High-Density Electrical Method in Detailed Karst Detection for Pile Foundation

Pile foundation construction in karst-developed areas commonly faces significant safety hazards. To accurately identify the distribution patterns of underground karst cavities and efficiently carry out grouting reinforcement around piles, this study utilizes a high-density resistivity method for detailed geophysical investigation within a pile group area at an intercity railway project in Guangzhou. By comparing inversion imaging results from densely spaced ZZ full-coverage arrays and Wenner arrays, the superior accuracy of the dense ZZ array in identifying geological anomalies and boundaries is verified. Based on field investigation data, the high-density resistivity method was applied to detect and re-inspect the pile group area before and after grouting, when the grout reached its designed curing period. Results show that the apparent resistivity of the pile group area increased overall from 30 Ω·m~70 Ω·m to 120 Ω·m~160 Ω·m after grouting, indicating effective filling. Among five major anomalies detected along multiple survey lines, four were consistent with borehole observations. Engineering practice demonstrates that the high-density resistivity method effectively identifies karst zones, water-rich cavities, and fractured rock zones, enabling scientific optimization of grouting designs and providing reliable geological support throughout the entire process of "detection—grouting—re-inspection".