Coupled thermohydromechanical analysis of Venice lagoon salt marshes

A fully coupled thermohydromechanical (THM) finite element approach is used here to model the groundwater and saturation response of a typical salt marsh of the Venice lagoon (Italy) subjected to both tide fluctuation and flooding. The soil forming the marsh, whose relevant material parameters have been measured experimentally in the laboratory, is assumed to be an homogeneous multiphase porous medium, in a thermodynamic equilibrium state both in fully saturated and partially saturated conditions. More particularly, the study is aimed at analyzing separately the various couplings of several factors such as soil stiffness, water conductivity, capillary suction, and humidity exchange with atmosphere including also the occurrence of marsh flooding on the overall mechanical response of the marsh subjected to tidal oscillations of very narrow amplitude. From the analysis carried out so far, the numerical approach adopted here seems capable of describing most of the relevant features of marsh behavior, thus showing the importance of THM couplings to explain the groundwater pressure evolution induced by lagoon tide cycles. In addition, the model seems to provide some interesting explanations concerning the evolving instability of marsh scarps, which is one of the main causes of the rapid overall deterioration of the typical Venice lagoon landscape.