Gypsum Dissolution Rate, New Data and Insights

Sinkholes linked to covered evaporite karst in urban environments still represent a challenge in hazard and risk assessment. The Quinis hamlet, located in Friuli Venezia Giulia region (NE Italy), is heavily affected by sinkhole phenomena (linked to an evaporitic bedrock), which deeply interested infrastructures and houses. In order to understand the evolution of the sinking phenomena, a field experiment started on the dissolution rate of the gypsum. In 17 existing piezometers, at different depths, 51 evaporitic rock samples were exposed to the naturally occurring variation of relative humidity, air flow and hydrodynamics. The rock samples were placed respectively in the aeration, in the fluctuation and in the phreatic section of the piezometric tubes. Data related to groundwater level fluctuations, temperature and electrical conductivity were collected. After four months, rock samples were removed, weighted and the volume loss evaluated. The obtained results indicate that rock sample reduction is not only dependent on the groundwater level fluctuations and on the number of days during which the samples are immersed in the groundwaters but also on the mineralization of the latter. Some of the rock samples have been almost completely dissolved, with dissolution rate values almost eight times bigger than expected if compared to the available literature data. The proposed approach had as aim to evaluate the quickness of the dissolution process, which is dependant on several causes (groundwater level fluctuations, type of rocks, chemical characteristics of the groundwaters, etc.) and represents a novel contribution to the overall knowledge of karst processes with noticeable impacts on human-built construction.