Laboratory experiment on water-rock interaction of the karst fracture water after recharged with roof rainwater

Simulation experiment is carried out to test the corrosive interaction between the Ordovician system limestone samples taken from the west campus of the Jinan University with the mixed water of different groundwater to rainwater ratio. The water-rock interaction among the original groundwater, aquifer media and rainwater being recharged is analyzed by means of determination of pH and electrical conductivity as well as several convention ions and using hydro-geochemical modeling software PHREEQC. The results show that,(1)after the groundwater and rainwater being mixed with each other, the CO2 pressure in the mixed water gradually decreases under the influence of temperature increase and decarbonation along with the oscillation; (2) Ca2+ concentration slightly decreases when mixing ratios of groundwater and rainwater are 9∶1, 7∶3 and 5∶5 respectively, while other ions concentration does not change obviously; (3)saturation indexes of calcite, dolomite and gypsum decrease along with reaction time, and saturation indexes of calcite and dolomite decrease obviously along with the increases of recharging rainwater amount, from 0.23~-0.39 and 0.05~-0.97 when the ratio of groundwater to rainwater being 9∶1 and from -0.34~-0.62 and -1.59~-2.57 when the ratio of groundwater to rainwater being 1∶9 respectively, which indicating that the rainwater is able to increase the corrosion to calcite and dolomite or even the whole aquifer and that the more the rainwater amount, the more obvious and stronger the corrosive effect; (4) rainwater recharge can only lead limited corrosion amount, so it won’t cause obvious impact on the stability of the aquifers around the well.