-
The Effect Of Flood On Roads Durability In Nigeria
CHAPTER ONE -- [Total Page(s) 3]
Page 2 of 3
-
-
-
In flood events, socio-economic life and livelihood of the affected
people may be distorted, in most cases farmlands and livestock are
submerged which are the major source of people’s livelihood. Flood
losses are devastating as many never get recovered after the flood
recedes. Vulnerable communities suffer great losses in events of flood,
especially when the flood is unprecedented. Hunger, famine, disease and
epidemic outbreak are usually resultant impacts of flood (Mmom and
Aifesehi, 2003). Malaria and typhoid outbreaks after floods in tropical
countries are common. It has been estimated that in India and Bangladesh
300 million people live in areas that are affected by floods (Nott,
2006).
It is well known that the rate of road deterioration increases
if the water content of the granular material increases. In rigid
pavements (i.e., concrete), temperature gradients across the concrete
slab can cause structural defects.Diefenderfer, et al. (2002).
Diefenderfer, et al. (2002) presents no less than six adverse effects
related to excess water: reduction of shear strength of unbound
materials, differential swelling on expansive sub grade soils, movement
of unbound fines in flexible pavement base and sub base layers, pumping
of fines and durability cracking in rigid pavements, frost-heave and
thaw weakening, and stripping of asphalt in flexible pavements. On the
positive side, ensuring proper (optimal) water content greatly improves
packing of the road during construction, and may also increase its
resilience when trafficked, even though this effect is often neglected.
It is generally desired to keep the road as close to or less than
optimum water content as possible over time as water and road
construction do not make for a harmonious couple.Dawson, A.R. (2009).
According
to McRobert, J. et al. (2000), Drainage is often described as the
central and most important aspect of design, construction and
maintenance of any road, including unsealed roads. Drainage of unsealed
roads can be of even greater importance because lower quality design and
construction standards and marginal materials are generally used, which
are more permeable to water. Poor drainage will reduce the life of the
pavement and have serious environmental impacts if left unchecked. There
are many approaches to reducing erosion of exposed surfaces associated
with unsealed roads, such as side drains, cut-off contour banks and
batter slopes. Any road will readily concentrate runoff, so there is a
need to design and construct roads to allow for frequent and safe
discharge.
During the rains, part of the rain water flows on surface
and part of it percolates through the soil mass as gravitational water
until it reaches the ground water. Some water is retained in the pores
of the soil mass and on the surface of soil particles which cannot be
drained by normal gravitational methods and this retained water is
termed Held water. It is required that the surface water from the
carriageway and shoulder should effectively be drained off without
allowing it percolate the sub grade. The surface water from adjoining
land should also be prevented from entering the roadway. The side drains
should have sufficient capacity and longitudinal slopes to carry away
all the surface water collected. This improper drainage system causes
the failure of road pavements due to many reasons such as increase in
moisture content, decrease in strength, mud pumping, formation of waves
and corrugations, stripping of bitumen, cutting of edges of pavement and
frost action.
CHAPTER ONE -- [Total Page(s) 3]
Page 2 of 3
-
