Landslide Mitigation - Semi-quantitative Approaches for Landslide Assessment and Prediction - page 227

Developing an inventory/database on landslide hazard.

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Development of awareness strategy and awareness programmes in the hazard
prone areas.

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With the establishment of National Disaster Management Act (NDMA) in 2005
some more responsibilities were entrusted to GSI as Nodal Agency which includes
assisting NDMA in drawing up the policies, plans, and guidelines in case of
landslide hazards and advise NDMA in technical matters.
Landslide mitigation works are to be conducted in order to stop or reduce the
landslide movement so that the resulting damages can be minimized. With a clear
understanding of the causes and mechanics of the landslide, the landslide control
works can be implemented in the Shivkhola Watershed. Basically,

landslide

mitigation works are broadly classi ed into two categories such as control works

and restraint works. The control works involve modi cations of the natural

conditions of landslides such as topography, geology, ground water, and other
conditions that indirectly control portions of the entire landslide movement. The
restraint works rely directly on the construction of structural elements. Landslide
control works involves surface drainage control works, sub-surface drainage control
works, soil removal works, buttress fill works, and the development of river

structure. The surface drainage control works can be accomplished with the
introduction of drainage collection work and drainage channel works. The drainage
collection works are to be designed to collect upslope water by introducing cor-
rugated half pipes horizontally at regular interval to reduce the length of over length
flow and to minimize the seepage. The drainage channel works are to be designed
to remove the collected water out of the landslide affected areas.
The sub-surface drainage control works are to be incorporated to remove the
ground water within the landslide mass and to prevent the inflow of ground water
into the landslide mass from the surrounding areas. This type of works are to be
achieved with the development of intercept under drains and trench drains,
horizontal gravity drains, drainage wells, and drainage tunnels investigating the
landslide prone area properly. Soil removal works are to be applied for small to
medium size landslides. The buttress fill is placed at the lower portions of the

landslide in order to counterweight the landslide mass. It is most effective if the
soils generated by the soil removal works are used.
Retaining walls are also to be constructed to prevent smaller sized and secondary
landslides that often occur along the toe portion of the larger landslides. Because of
the large-scale earth-movement and numerous springs that are expected in landslide
terrain, crib walls are common instead of conventional reinforced concrete retaining
walls. The anchor works utilize the tensile force of anchor bodies embedded
through the slide mass and into stable earth, and are connected to thrust blocks
located on the ground surface. The thrust blocks are anchored with a tendon that
counteracts the driving forces of the landslide to restrain the slide movement.
The protection measures which could be adopted to reduce the risk of landslide
may broadly be grouped into following heads (Selby 2005 ):