, Available online , doi: 10.11932/karst2025y021
Abstract:
The karst regions in southwestern China are characterized by intense karstification, complex hydrogeological conditions, and well-developed karst conduits with pronounced spatial heterogeneity. These factors contribute to the inherent vulnerability of karst groundwater systems, rendering them highly susceptible to contamination. Additionally, large-scale mining activities in these areas generate substantial volumes of wastewater and waste materials, exacerbating groundwater pollution. Consequently, the development of scientific technologies for the prevention, control, and assessment of groundwater pollution is of significant importance. This study focuses on the Zimudang mining area in Guizhou Province, where curtain grouting experiments were conducted to seal identified karst conduits, targeting the dominant hydraulic pathways of groundwater contamination. Real-time in-situ monitoring using electrical resistivity methods was employed throughout the grouting process to evaluate the effectiveness of the sealing measures.The Zimudang depression is a critical surface water convergence area within the study region, where the converging surface water is transformed into groundwater through the K20 drainage cave located beneath a steep cliff on the northeastern side of the depression. Mining activities have compromised the water-blocking function of the F1 fault, altering the groundwater flow so that it converges toward the mined-out areas and mining tunnels. Within the mining area, the K20 drainage cave serves as a channel for the concentrated recharge of groundwater by atmospheric precipitation; once entering the K20 drainage cave, the principal karst hydraulic conduits extend roughly in an east−west direction. Taking into account the characteristics of subterranean river channels, topography, and surface structures, the curtain grouting test site was determined to be located in the northern part of the tailings pond. Drilling and borehole television surveys were conducted at the site, and analysis of core logs and borehole TV results confirmed significant karst development in the underlying strata, which serve as the dominant hydraulic pathways for groundwater contamination migration. To ensure that the grout solution adequately permeates and fills fractures and karst cavities, high-pressure intermittent grouting was adopted, with grouting performed sequentially from ZJ08 to ZJ01, followed by a second round after the injected grout cooled. Throughout the entire grouting process, high-density resistivity and transient electromagnetic methods were employed to monitor changes in formation resistivity.In this experiment, one high-density electrical measurement line and eleven transient electromagnetic measurement lines were deployed. Three electrode configurations—Wenner, dipole, and Schlumberger—were utilized, with measurement depths of 15 m, 15 m, and 17 m, respectively. All three configurations demonstrated a clear increase in formation resistivity within the grouted zone, with the low-resistivity regions adjacent to the boreholes exhibiting more pronounced improvements post-grouting. For instance, among the transient electromagnetic measurement survey lines (S3, S5, S7, S8, S10, and S11), significant increases in formation resistivity were observed in lines S3, S5, S7, and S8, indicating effective grouting and sealing. In contrast, lines S10 and S11 showed either negligible changes or a decrease in resistivity after grouting. This discrepancy is attributed to the fact that line S10 was situated beyond the grouting influence zone due to its distance from the grouting wells, while line S11 exhibited localized resistivity reductions, likely caused by the displacement of water from karst cavities and fractures as grout infiltrated these features. Analysis of the geophysical monitoring data revealed that the high-density electrical method is more suitable for detecting shallow resistivity variations in areas with limited terrain, whereas the transient electromagnetic method is more effective for characterizing deeper subsurface electrical properties.To quantitatively assess the grouting effectiveness, formation porosity was derived from resistivity measurements using Archie's formula. By comparing porosity variations before and after grouting, the grout diffusion area was delineated, and the effectiveness of blocking groundwater pollution pathways was evaluated. For instance, in measurement lines S3, S5, S7, and S8, the grout diffusion area within a 2-meter radius of the grouting wells ranged from 21.42 to 99.32 m2. The maximum reduction in formation porosity reached 65.7%, with an average porosity reduction of 39.9%. This study demonstrates that electrical resistivity monitoring enables real-time in-situ evaluation of the grouting sealing effectiveness in karst conduits. In addition, by converting resistivity data into formation porosity for quantitative analysis, it is possible to accurately delineate the grouting diffusion area and sealing range, thereby assessing whether key hydraulic pathways have been effectively sealed. This approach provides robust technical support for evaluating the performance of curtain grouting in blocking the dominant groundwater contamination pathways in karst regions.
