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RISK
ANALYSIS
AND
REMEDIAL
WORKS AT
KAAIMANS
PASS
Monyake Mohlabane
• According to the climatic data for the George
area for the 30-year period from 1961 to 1990:
– the average rainfall for the month of August is 68mm
– the highest 24 hour rainfall measured for the month of
August is 116mm
– the highest 24 hour rainfall measured for any month is
132mm, and
– the recorded rainfall for Knysna during August 2006
was 377mm.
• From the above it is evident that the rainfall of
August 2006 in the George to Knysna area was
abnormal compared to the statistics of the past
30 years.
METHODOLOGY OF INVESTIGATION
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Visual Inspection of Failures (walkover survey)
Visual Inspection of Structures (distress)
Aerial Inspection (full extend of failures)
Route Mapping (geology & mapping)
Aerial Photography (stereo-pairs & contours)
High Resolution Aeromagnetic Survey (faults)
Rotary Core Borehole Drilling (remedial works)
Exploratory Trenches (failure surface)
Installation of Inclinometers (monitoring)
• Several modes of failure were evident
along the National Road N2/7, including:
– translational failures (i.e. sloughs) in relatively shallow
soil overburden,
– slip circle failures in moderately thick soil layers,
– plane failures in rock slopes,
– wedge failures in rock slopes,
– undercutting (erosion) of embankments and talus
slopes,
– hillcreep on steep slopes, and in addition,
– significant erosion gulleys occurred along some of the
preferential drainage paths
• A probability of failure analyses was
carried out at each of the analytical
sections along the route. The probability of
failure type analysis was chosen because
it can evaluate the sensitivity of more than
one design parameter and its overall
contribution to slope stability.
The most significant types of failure
encountered along the route were:
• Translational slides in relatively
shallow soils
• Wedge failures in rock masses
• Planar failures in rock masses.
Major Planar Failure (Ch35+180)
Failure surfaces with Sub-vertical Release Joints
(Ch35+180)
Meshing and Pinning of Colluvium at Crest of
Slope (Ch35+180)
Rockbolting of Rock Slabs (Ch35+180)
Slope Cleared of all Failure Debris (Ch35+180)
Granite Corestones / Soil Matrix on Foliation
Plane (Ch35+950)
High Pressure Water Jetting of Talus Face
(Ch35+950)
Scaffold Structure utilised to Access Talus Face
(Ch35+950)
THANK YOU