Measuring the Effect of Grass Roots on Shear Strength Parameters of Sandy Soils

Measuring the Effect of Grass Roots on Shear Strength Parameters of Sandy Soils

Cohesionless soils such as sandy or silty soils are more susceptible to landslides, slope failures, and erosion in comparison with cohesive soils containing clayey fraction. While vegetation roots are known to provide erosion resistance, shear strength properties of cohesionless soils with grass roots and their effect on slope stability needs more investigations. Therefore, it was decided to test soil specimens of cohesionless soils with and without grass roots in the laboratory. The objective of the testing program was to quantify the effect of grass roots on cohesion and angle of internal friction of the sandy soils. Direct shear tests were conducted on specimens (with and without grass roots) consisting of three types of soils: (i) natural fine silty sand, (ii) clean sand with medium and subangular particles, and (iii) clean sand with angular coarse-grained particles. The effect of grass root was more pronounced in fine silty sand with about 210% increase in cohesion and about 13% increase in the angle of internal friction. The test results indicated that the presence of grass roots increased the cohesion by an average of 119% while the angle of internal friction was found to have increased by an average of 12% among the soils tested. For the tested sands, the inclusion of grass roots was found to increase the factor of safety by 550% for slopes in dry conditions, whereas the factor of safety increased by 525% for slopes with seepage conditions.

Ryan Cardoza is a former Fresno State graduate student.

conference paper

Cardoza, R., & Oka, L. (2020). Measuring the Effect of Grass Roots on Shear Strength Parameters of Sandy Soils. Geo-Congress 2020, 214–223. https://doi.org/10.1061/9780784482834.024