Mitigation measures of rockfall hydrogeological risk

Type of intervention: Mitigation measures of rockfall hydrogeological risk

Issue: The site is characterized by a high level of dangerousness due to landslides. Along the site’s upstream side, the geological evolution led to the boulder disintegration. After some boulders’ fall near a building downstream the rock wall, it was necessary to plan this project, aimed at identifying appropriate measures to secure the slope.

What we proposed: We proposed the execution of detailed geological and geomechanical surveys in order to identify possible detachment points and areas marked by a greater probability of detachment.

Afterwards, we have considered protection systems combined with passive and active works. This choice is due to the particular geomorphological characteristics of the area and the proximity between rocky wall and buildings.

• The active systems are located along the most critical areas. These works are made of double twisted hexagonal wire mesh sections woven with drawn iron; horizontal AMZ ropes arranged at the top, foot and centre of the area keep them adherent to the wall. This intervention involves galvanized metal anchor bolts.
• The passive protection system requires the installation of an elastic rockfall barrier, which allows to stop the falling blocks; the boulders will then bounce along the slope.

How we act: Through 12 geomechanical stations and the deposited blocks’ census, it’s been possible to define the boulder’s geological and structural parameters, the possible detachment volumes and the GSI and RMR resistance parameters. We performed an accurate numerical modeling only after considering:

• rocks physical and mechanical characteristics,
• conditions of the discontinuity joints,
• breaking mechanisms of the rock mass and
• geometry of unstable boulders.

The blocks falling from the rocky slope above the area was simulated using softwares like “QGis” and “Rockyfor3D”. The simulation showed that, without defense work, the blocks falling from the detachment areas affect the road and the buildings downstream.

Therefore, it was possible to verify the effectiveness of designed active-passive protection works in sensitive areas.