In situ Shear Tests of Soil Samples with Grass Roots in Alpine Environment

Problem statement: The presence of vegetation increases the soil burden stability along slopes and reduces soil erosion. Its contribution is due to mechanical (reinforcing soil shear resistance) and hydrologic controls on streambank and superficial landslides. This study presented the results carried out from experimental in situ test focused to study the increased shear resistance of soil blocks due to root-reinforcement. A shear apparatus was set up in order to realize the measure. Approach: In this research the researchers tested the capacity root reinforcement of Festuca pratensis, Lolium perenne and Poa pratensis (Poaceae families), Medicago sativa, Trifolium pratensis and Lotus corniculatus (Fabaceae families) grass species widespread in the Alpine environment. Results: In situ shear tests results revealed that grass roots fail progressively and their tendency were to slip, without failing. Shear-strengths calculated for root-reinforced soil with Fabaceae, yielded values between 19 and 166% higher than directly measured shear-strengths in soil with no roots. The shear displacement had an increase included between 493 and 1.900%. The shear time was always superior. The clod with roots, after the trials, were always packed together. Conclusion: These data were lower than those obtained with Poaceae tests (from 50-318%), but the two grass families were functional for a grass mix useful in technical seeding.