Detection Methods for Unfavorable Geology and Soil Caves before Grouting in Karst Terrains: Fid-Bau Portal

Detection Methods for Unfavorable Geology and Soil Caves before Grouting in Karst Terrains

Cao, Ruilang / Feng, Shangxin

In karst terrains with numerous soil caves and well-developed hydraulic flow channels it is important to document the spatial distribution of the geological hazard zones before a grouting program is initiated. These zones may well lead to excessive grout leakage that would require additional work to make the grout curtain effective. During the geological survey of the Dehou Reservoir site in Yunnan province, China, a combined survey method, including drilling process monitoring (DPM), cross-hole electrical resistivity tomography (C-ERT), and water pressure testing in boreholes (WPB), was used to identify the geological hazard zones in the karst terrain between grout curtain boreholes. The results from this survey showed that an integrated investigation can define the stratigraphic characteristics necessary to complete grouting projects successfully. The DPM, C-ERT, and WPB can be used to determine the locations of the preferential grout flow paths and the soil caves around a single borehole and map the distribution of unfavorable geology between boreholes. The data collected were sufficient to allow appropriate grouting parameters to be defined. Based on the analysis of the data obtained, empirical relationships between the penetration rate, the permeability, and the electrical resistivity were developed to evaluate the groutability of strata in this karst terrain. The mutually verifiable data obtained from these combined methods can lead to accurate and practical survey results.