Limestone stratum has great anisotropy, which is distributed from large karst caves, pipelines, and faults to small solution pores, and crevices. In this paper, uniaxial compression tests of solution pore and crevice limestones from Mamaya I hydropower station and Ronglai hydropower station are conducted, and the porosity of these limestones is measured. The results show that there is a good power function relationship between compressive strength and the porosity of the solution pore and crevice limestone. Based on the Hoek–Brown criterion, the method for determining mechanical parameters of the solution pore and crevice limestones is proposed, taking the porosity of the rock into consideration. Then, the relationships between the rock mass parameters m b , s, and a and the porosity n are deduced. Based on the proposed method, the variation laws of the mechanical parameters of the limestones, including uniaxial compressive strength (UCS), tensile strength, deformation modulus, shear strength parameters are analyzed. The proposed method simplifies the complexity of mechanical parameters selection by quantifying GSI, avoids the subjectivity and uncertainty, and has good reliability and suitability in the pore and crevice limestone stratum, which has a certain guiding significance for the construction of similar sites.

No abstract

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.