Application of Direct Shear Testing to Assess the Influence of Mangrove Root Structures on the Shear Strength of Coastal Wetlands

Document Type

Conference Proceeding

Publication Date

1-1-2025

Abstract

Mangrove ecosystems in the northern Gulf of America are expanding due to climate change, yet their resilience to extreme events and shifting coastal conditions remains uncertain, particularly regarding the understudied role of mangrove roots in sediment stabilization. In Louisiana and Texas, mangrove stands develop under distinct environmental pressures - Louisiana's river-dominated deltaic systems experience high sediment deposition, organic-rich soils, and subsidence, while Texas' tide-dominated lagoons are shaped by hydrodynamic forces and coarser sediments. This study uses direct shear testing (DST) to evaluate belowground biomass (BGB) and necromass (BGN) effects on soil strength in Louisiana and Texas mangroves. Results indicate that BGB and BGN are higher in Port Fourchon, LA, than in East End Lagoon, Galveston, TX, with root mass decreasing consistently with depth in both basins. DST results revealed that top samples from both basins and mid samples from Port Fourchon, LA, exhibited strain-hardening behavior, where shear resistance increased due to root reinforcement. This effect was absent in mid samples from Galveston, TX, likely due to lower root mass. In contrast, bottom samples showed strain-softening behavior, characterized by a peak followed by a decline in shear strength, reflecting reduced root reinforcement at greater depths. The strong correlation between shear strength and live root mass confirms that root reinforcement is a key factor in soil stability, though sediment composition also plays a role. These findings enhance our understanding of how mangrove root systems contribute to soil stabilization, providing insights for identifying areas more resilient to sea-level rise and supporting a mechanistic framework for the design of conservation and restoration projects in the northern Gulf of America.

Publication Source (Journal or Book title)

Geotechnical Special Publication

First Page

130

Last Page

140

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