12.8 The Reinforcement of Soil by Roots: Recent Advances and Directions for Future Research

Abstract

Mechanical strengthening of a soil occurs as a result of reinforcement by the roots, due to their tensile strength, frictional, and adhesional properties. Soil is strong in compression but weak in tension; conversely, plant roots are weak in compression but strong in tension. When the two are combined they, therefore, produce a matrix of reinforced earth, which is stronger than the soil or the roots separately. Root tensile strength tends to decrease nonlinearly with increasing root diameter, with root strength having been found to be closely correlated to cellulose content and, therefore, the biotic and abiotic factors that determine cellulose production in roots. Techniques for modeling root–soil interactions have improved significantly over the last 5–10 years with the introduction of fiber-bundle models to the study of root reinforcement. Although the mechanics of root breaking, stretching, compression, and pullout can be modeled successfully, several obstacles to more accurate root-reinforcement predictions remain, including the collection of accurate field data to parameterize these models over different spatial and temporal scales. Root-reinforcement modeling has, however, shown that roots can be of significant importance in the stabilization of slopes and streambanks affecting both the timing and magnitude of mass failure events, and the geomorphic processes that cause them.