Soil bio-engineering techniques to protect slopes and prevent shallow landslides

Soil bio-engineering techniques consist in the use of plants, often combined with wooden structures, for the protection and reinforcement of soil and contextually for the re-naturalization of anthropic areas. They are often possibly adopted in place of traditional geo-engineering works because of ecological and economic benefits although a deeper knowledge of their actual mechanical action is requested by practitioners. The present contribution was developed in the framework of a research project focused on the mitigation of landslide risk and is divided into two parts. After a brief overview of the most common soil bio-engineering practices, the results of experiments that were performed on plant roots and on rooted soil samples are shown and discussed in the first part of the paper. Indeed, the role of roots, which is fundamental in almost all soil bio-engineering techniques, is emphasized by the practice of re-vegetation. Presently, the mechanical action of roots on a saturated sandy soil undergoing shear strain, is identified at the scale of volume element. Advantages and limits of Wu and Waldron’s model, which is frequently used to estimate the contribution of roots to the soil shear strength, are also investigated. In the second part of the paper, a general description of live wooden cribwalls is given which is aimed at making practitioner aware of the effectiveness of this technique to retain cuts a few meters high and guarantee the stability of slopes. The mechanical contribution of plants, that progressively enhance the performance of cribwalls, is shown in terms of increments of the safety factor of the structure.