Experimental study on the detection of karst pores by cross-hole CT imaging and groundwater occurrence in the Luxi karst fault-depression basin

Around the Jibi village southwest of the Luxi fault-depression basin, carbonate is widely distributed with well developed highly uneven karst. The surface is dominated by dissolution cracks and gullies with numerous mosore and some karst wells, one of which exposes as a big spring at the Jibi village. This work built on an 1∶10,000 hydrogeology survey. Using the high-density electrical method section，rapid scanning，combined with the IP sounding, locations of two boreholes to be drilled were determined,where the demonstration holes SK1 and SK2,48 m apart,were drilled.Then cross-hole CT imaging was conducted to detect the underground karst development and groundwater occurrence state. The results show that the cross-hole CT results are largely consistent with drilling interpretation, permitting to reveal the underground karst and groundwater occurrence. While the conventional geophysical methods can only speculate the geology in vertical direction, not clarifying horizontal fracture zones and karst caves. Combination of cross-hole electromagnetic and drilling can just can make up this deficiency. In carbonate formation,according to attenuation values of electromagnetic wave energy from different emission angles in the underground space,this approach allows to use inversion algorithms to calculate the absorption coefficients of underground media,reconstruct 2D images of the absorption coefficients in profiles between boreholes, and infer the occurrence of karst and groundwater in the subsurface. The detection results of cross-hole electromagnetic CT in the Luxi karst fault-depression basin show that this method is feasible and effective，and provides support for better arrangement of boreholes.