In situ shear tests of soil samples with grass roots in Alpine Environment.

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 superficia landslides. This study presented the reuslts 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. Results. In situ shear tests results revealed that grass roots fail progressively andtheir tendency were to slip, without failing. Shear-styregths calculated for root-reinforced soil with Fabaceae, yielded values between 19 and 166 % higher that directly measured shear-strength in soil with no roots. The shear displacement had an increase included beteen 493 and 1.900%. The shear time was alaways superior. The clod with roots, after the trials, were alaways together. Conclusion. These data were lower that those obtaioned with Poaceae tests( from50-318%), but the two grass families were functional for a grass mix useful in technical seeding.