Environmental Engineering Reference
In-Depth Information
RS/R, Very steep,
unstable slope
RS/R, (decomposed/fractured)
very steep slope
Old debris
slide scar ?
3
1
2
RS/R, steep slope
with seepage
2
4
Strong erosion
Old and new debris slid
CS and RS/R, very thin
cover good drainage
generally stable
Loose blocks
1
55
3
In general, sound to lightly
fractured granite gneiss
EI. +900 m
RS/R with trees inclined
Fill-supported pavement settlement
3
Thick CS, very
steep slope
Recent debris
slides
54
Legend - hazard rating
1. Vey high
2. High
3
(see text)
3. Moderate
1
4. Low
Fill-supported pavement settlement
Cuts with old debris slide scars, very sttep slope
with thin cap RS/R. Drainage is around cuts aiding
stability. some small erosion in cuts
Legend - geology
RS- residual soils
Cs- Colluvial soils
R- rock
- drainage channels
kilometer (old)
kilometer (new)
3
55
95
Thin RS/R, moderate slope inclination
Thin RS/R on steep slope
3
4
Vertical cut in granite, sound, massive, tightly jointed
53
3
Thin RS/R, fractured and inclined, seepage
4
3
2
Recent debris slide
Figure 9.97 km 52.5-53.5
3
3
3
1
Old shallow slump in RS
2
RS/R, steep slope
with seepage
Fill with erosion
FIGURE 9.97
(Upper left) km 52.5-53.5.
2
Thin RS/R on very steep slope
4
Vertical cut, fractured rock,
loose blocks
2
Old anchors sabilizing fractured rock
51
Concrete curtain, wall supporting fill
2
Low concrete wall supporting slope
CS and RS, inclined trees
4
Slope with very little soil cover
old debris slide scar, little soil remains
SR/R, potentially unstable
4
3
RS/R, old debris slide scars
2
4
X EI. +1200 m
52
RS/R, very steep slope
with seepage
3
2
4
Loose blocks in overhanging cut
2
3
4
4
Old debris slide scar
Strong erosion of fill near
pavement on steep slope
Erosion along top of high, steep cut,
loose blocks in lower portions
4
1
4
50
95
Old debris slide, inclided
frctured rock
Old debris slide on inclined rock surface
3
3
3
Old debris slide scar
CS with much slope
seepage
Thin SR/R (inclined rock surface)
2
Fills suffering erosion
3
2
3
3
CS but with good
natural drainage,
small slumps
possible
EI. +550 m
2
RS/R (inclined surface), unstable
96
3
4
3
Old debris slide scar, RS/R (decomposed)
New
wall
occasional small debris slides in steep cut,
but well back from pavement
49
3
Strong erosion undercutting fill
close to road
97
48
Small slump in CS(recent)
Scale: 0
100
500 m
47,7
FIGURE 9.98
Slope failure hazard map for an existing roadway subject to numerous failures (BR-116, Rio de Janeiro, Brazil).
A panorama of the road between km 52 and 53.5 is shown in the photo (Figure 9.97). A debris avalanche that
occurred at km 56 is shown in
Figure 9.10.
The Slope Failure Hazard Map
The map (Figure 9.98), prepared by the author during a 1979 study, illustrates the location
of cuts and fills, drainage, and the degree of hazard. Maps accompanying the report gave
geologic conditions and proposed solutions. The maps were prepared by enlarging rela-
tively recent aerial photographs to a scale of 1:10,000 to serve as a base map for plotting,
since more accurate maps illustrating the topography and locations of cuts and fills were
not available.
Five degrees of hazard were used to describe slope conditions:
1.
Very high
: Relatively large failures will close the roadway. Slopes are very steep
with a thin cover of residual or colluvial soils over rock, and substantial water
penetrates the mass. Fills are unstable and have suffered failures.
