Geologic Hazards - Geotechnical Engineering Investigation - page 791

TABLE 9.9
Failure Forms: Typical Preventive and Remedial Measures

Failure Form Prevention daring Construction Remedial Measures

Rock fall Base erosion protection Permit fall, clean roadway

Controlled blasting excavation Rock bolts and straps

Rock bolts and straps, or cables Concrete supports

Concrete supports, large masses Remove loose blocks

Remove loose blocks Impact walls

Shotcrete weak strata

Soil fall Base erosion protection Retention

Planar rock slide Small volume: remove or bolt Permit slide, clean roadway

Moderate volume: provide stable Remove to stable inclination or bolt

inclination or bolt to retain
Large volume: install internal Install internal drainage or relocate

drainage or relocate to avoid to avoid

Rotational rock slide Provide stable inclination and Remove to stable inclination

surface drainage system Provide surface drainage

Install internal drainage Install internal drains

Planar (debris) slides Provide stable inclination and Allow failure and clean roadway

surface drainage control Use preventive measures

Retention for small to moderate
volumes
Large volumes: relocate

Rotational soil slides Provide stable inclination and surface Permit failure, clean roadway

drainage control, or retain Remove to stable inclination,

provide surface drainage, or retain
Subhorizontal drains for large
volumes

Failure by lateral Small scale: retain Small scale: retain.

spreading Large scale: avoid and relocate, Large scale: avoid

prevention difficult

Debris avalanche Prediction and prevention difficult Permit failure, clean roadway:

Treat as debris slide eventually self-correcting

Avoid high-hazard areas Otherwise relocate

Small scale: retain or remove

Flows Prediction and prevention difficult Small scale: remove

Avoid susceptible areas Large scale: relocate

Hazard Reduction
The hazard can be decreased by partially reducing the height and inclination or adding
material at the toe; by planting vegetation, sealing cracks, installing surface drains, and
shotcreting rock slopes; and by controlling internal seepage. In the last case, one can never
be certain that drains will not clog, break off during movements, or be overwhelmed by
extreme weather conditions.

Time Factor
Where slopes are in the process of failing, the time factor must be considered. Time may
not be available for carrying out measures that will eliminate the hazard; therefore, the
hazard should be reduced and perhaps eliminated at a later date. The objective is to arrest
the immediate movement. To the extent possible, treatments should be performed during