CIVIL WORKS GUIDELINES FOR MICRO-HYDROPOWER IN NEPAL
9
Photo 2.1 Tension cracks along a slope
Photo 2.2 Obstruction caused by debris falling from on unstable slope
could significantly impact the project. If available, a geological
map of the area where the micro-hydro scheme is proposed
should be consulted to avoid placing civil structures on these
major thrusts and faults. If circumstances dictate the inevitabil-
ity of placing the scheme in such zones, expert help from a
geologist should be sought.
2.4.3 SLOPE STABILITY
In geological terms, the hills and mountains of Nepal are young
and unstable. They could be likened to a pile of sand in that
the excavation along a slope easily results in the sliding of
the land above, especially when a further triggering
mechanism occurs (particularly during the monsoon).
Common triggering mechanisms are the following:
Surface water
Ground water
Undercutting of slope by excavation
TABLE 2.1 Indicators of slope instability
SECTION OF SLOPE
Upper, middle or lower hillslopes
Exposed faces of landslides
Debris slopes
INDICATOR OF INSTABILITY
Tension cracks along slope (Photograph 2.1), ground shelves sharply, trees
leaning downslope or bending upwards from the base, water springs or
seepage at base of slope, displacement of paths, fence or posts.
Fresh rock faces exposed, presence of soft, weatherable rock, open joints in
rock, tension cracks, overhangs and loose rock, water springs or seepage
at base of rock face.
Fresh debris at base of slope, tree roots exposed, loose debris which
moves underfoot, profiles steepen towards base of slope, debris littered
with dead or overturned woody plants and grass clumps.