ROCK FALLROCK FALLHAZARDSHAZARDS

Part 12Part 12

RockfallsRockfalls

• Rockfalls are a Rockfalls are a common problem common problem along highways in along highways in mountainous mountainous terrainterrain

• They can be costly They can be costly and deadly; easily and deadly; easily triggered by short triggered by short bursts of intense bursts of intense precipitationprecipitation

• Many rock masses are Many rock masses are mixturesmixtures of dissimilar of dissimilar materials with markedly contrasting materials with markedly contrasting stiffness, as seen in this glacial till stiffness, as seen in this glacial till

Rock FallsRock Falls• 70% of all rockfalls

occur during the initial fall freeze or initial spring thaws

• Rock falls are generally driven by pore pressures, not by the volume of water. Its all about pressure, not volume.

• Standard Standard guidelines exist guidelines exist for mitigating for mitigating damage from damage from rockfallsrockfalls

• These include These include debris ditches, debris ditches, rock fences, and rock fences, and placing mesh on placing mesh on the raveling the raveling slope using slope using rockboltsrockbolts

Rockfall MitigationRockfall Mitigation

Triple twisted galvanized or PVC coated gabion wire Triple twisted galvanized or PVC coated gabion wire mesh is an excellent structural material to employ on mesh is an excellent structural material to employ on raveling rock slopes where insufficient right-of-way raveling rock slopes where insufficient right-of-way exists to construct a catchment ditch and fence.exists to construct a catchment ditch and fence.

Some mechanism for periodic mucking of Some mechanism for periodic mucking of accumulated debris should be incorporated into the accumulated debris should be incorporated into the remedial schemeremedial scheme

Most rockfalls occur during first significant freeze or Most rockfalls occur during first significant freeze or thaw cycles thaw cycles

Design details for typical Design details for typical rockbolt stabilization scheme rockbolt stabilization scheme on raveling rock cut slope on raveling rock cut slope (from Rogers, 2003)(from Rogers, 2003)