Large-Scale Laboratory Direct Shear Testing for Wetland Root Strength

Wetlands act as a line of defense against the increasing impacts of hurricane storm surge and waves, rising sea levels, and the effects of changing weather patterns. Evaluating the wetland soil-root matrix shear strength is challenging due to both the complex nature of roots and the differences in live biomass and necromass volume with depth. Reasonable estimates of the root matrix shear strength in a horizontal mode of shear were developed using a large-scale direct shear apparatus (LDSA). Test beds for this study are the Atchafalaya and Terrebonne Basins in Louisiana; three sites were selected per basin across a salinity gradient of fresh to saline marsh. Initial findings indicate that the stress-displacement response witnessed an upward curvature. This behavior is attributed to the effect of the longitudinal and diagonal roots on the shear strength of the soil-root matrix when the shear plane cuts along the roots.