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Places where the steepness of slopes greater than 60% and existing
buildings are poor houses and/or do not promote proper retaining of
the slope.
The above criteria prioritizes risk situations involving loss of life
compared to those that would tend to produce only material losses.
The delimitation of areas with different risk situations depends on the
correct characterization of the processes of instability, also enabling the
demarcation of the area potentially subject to its effects. Thus, depending
on the mechanism of instability and position of the indicators of instability,
it identifi es the boundaries of the sector risk, which should include the area
directly involved in the initiation process, the passage area of the mass and
area of unstabilized deposition of material resulting from the destabilization
process (Carvalho 2000).
After completion of the zoning phase, the process of registration of
risk situations begins. As stated earlier, the risk register should provide
specifi c information about the risk level of houses in priority areas of risk,
defi ning the necessary interventions, economic and social characteristics
of families, environmental issues, providing a subsidy for monitoring
actions of civil defense, temporary removal of residents during heavy rains,
implementation of emergency stabilization works, etc.
It is interesting to note that in the risk analysis in slums, not only
housing is regarded as an element of risk, but also the urban infrastructure,
industries, traffi c routes for vehicles and pedestrians, and other elements
of infrastructure.
At this stage it is necessary to supplement the information gathered
during the risk zoning, through fi eld inspections and bibliographic data
(maps, charts, etc.), with a campaign-specifi c geotechnical investigation to
measure the soil strength parameters involved in processes of destabilization,
confi rming or correcting the degree of risk as defi ned above and providing
subsidies for the proposed interventions, either through monitoring or
works of geotechnical stabilization and consolidation. With regard to the
geotechnical studies at this stage of registration, must be alert to the presence
of preparatory and starting agents of risk situations, clearly defi ning the
mechanisms of instability. The preparatory agents may be geomorphologic
character (natural slopes, drainage lines, weakness planes, schistosity of
rock, etc.), geotechnical character (thickness of the layers and shear strength
of the same, the existence of steep cuts, landfi lls thick launch of trash and
debris on the slopes, etc.) or hydraulic character (concentration of runoff,
erosion, saturation of the subsoil, infi ltration trenches or wells, sewage spills
on the slopes, etc.). The starting agents can be heavy rains, cuts in unstable
material, embankments on soft soils, concentrated overloads (houses with
direct foundation, accumulation of various materials, earthquakes, etc.).
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