Integrating Portable Loading Tests and Hydro-Geomechanical Modeling to Understand Salt Marsh Subsidence in the Venice Lagoon

Salt marshes are vital coastal ecosystems that provide critical services such as coastal protection, biodiversity support, and carbon sequestration. However, these environments face significant threats from climate change and human activities, particularly in terms of subsidence and their ability to adapt to sea-level rise. This study investigates the geomechanical behavior of salt marsh soils in the Venice Lagoon through a combination of in-situ loading experiments and hydro-geomechanical modeling. The in-situ experiments were conducted at three sites: Le Saline, La Grisa, and Lazzaretto Nuovo. These experiments analyzed soil compaction under controlled loading and unloading conditions, highlighting variations in soil displacement due to differences in root density, sediment composition, and organic content. Results showed that shallow soil layers exhibit significant nonlinear behavior influenced by vegetation, while deeper layers demonstrated more elastic properties. A three-dimensional mixed finite element model was developed to simulate these processes, incorporating coupled groundwater flow and soil equilibrium equations. The model successfully replicated the observed experimental behavior, providing insights into the factors driving salt marsh compaction, such as sediment stratigraphy, hydraulic conductivity, and preconsolidation stress. Sensitivity analyses underscored the importance of these parameters in predicting marsh resilience to environmental stressors. This research contributes to understanding the interplay between hydro-geomechanical properties and salt marsh stability, offering valuable guidance for conservation and restoration strategies to preserve these essential ecosystems amid ongoing environmental challenges.