Creep-induced subsidence along coastal Louisiana with GPS measurements and finite element modeling

Abstract

Subsidence rates typically range between 2−7 mm/yr over the past one or two decades, as observed through GPS measurements at continuously operating reference stations along coastal Louisiana. The creep mechanism in Holocene sediments is adopted to quantitatively interpret the observed land subsidence along coastal Louisiana. An extended elasto-viscoplastic model is developed and implemented in ABAQUS. The material model is calibrated and validated based on both creep and constant rate of strain laboratory experiments conducted on Batiscan clays. Finite element models are then constructed to analyze creep-induced subsidence in Holocene sediments at four stations along coastal Louisiana. These models are calibrated with GPS-derived subsidence data to ensure consistency with measured values. Typical material parameters are used for lightly overconsolidated soils in the extended elasto-viscoplastic model. The modeled subsidence exhibits a negative correlation with both the initial overconsolidation ratio and strain-rate exponent. Subsidence accumulates over time at a decreasing rate. Creep-induced subsidence is predicted at four stations based on the calibrated finite element models, revealing an estimated 30.4 cm of subsidence over a span of 50 years (from 2005 to 2055) at station GRIS in Grand Isle. The significance of this study includes various aspects. The extended elasto-viscoplastic model improves the characterization of viscoplastic deformation in overconsolidated soils, typically associated with small strain rates (e.g., ɛ̇<10−8 s−1) observed in field measurements. The role of creep in subsidence in coastal Louisiana is confirmed, through a combination of GPS measurements and finite element modeling. The mechanism-based prediction of creep-induced subsidence can be applied to locations beyond coastal Louisiana.