Monitoring Methodology Study of a Reservoir Built on the Karst Depression: A Large Scale Laboratory Simulation Test

The karst depression with a natural negative landform is favorable for reservoir construction with less excavation work. The underground air-water pressure would be complicated after the construction of a reservoir that blocks the natural air-water channel (sinkhole, karst channel, etc.). To develop a monitoring system for the reservoir, a large-scale laboratory simulation test was carried out to study the air-pressure evolution and water migration process during water table fluctuation after the blockage of the sinkhole in a karst depression. The results are as follows. (1) The positive pressure jacking effect and the negative pressure sucking effect were observed in the karst channel and inside the model during groundwater table fluctuation. (2) A water imbibition test on the rock-like material was carried out with layered resistivity and layered NMR measurement. The relationship of resistivity and water saturation was developed based on Archie's equation. (3) The resistivity evolution during the test was monitored using the high-density electronic resistivity imaging method. The resistivity of the measured profile was sensitive to the variation of the water level, and the water migration process was quantified by the resistivity to water saturation conversion. (4) The suitability of many techniques for monitoring a reservoir built on the karst depression was discussed. The resistivity monitoring technique combined with the air-water pressure monitoring technique could provide useful information for safety and reliability assessment.