Rural road construction and networks are vital to regional economic development.
The road construction is one of the fast growing man-made projects. Research
shows that the least 15%-20% of the land in the world has been affected by road
networks (Way et al., 2005;
Juan et al., 2007). The current status of the advanced road network
has opened up new possibilities for many people in terms of accessibility. Still
this road network and its traffic flows have also produced negative effects
on local inhabitants and the surrounding flora and fauna (Jaarsma
and Van Dijk, 2002; Parsakhoo et al., 2008).
Without physical access, rural communities face obstacles in take advantage
of crop production. Rural road conditions the development perspectives of agriculture
and recreation, as well as some possibilities of agriculture related preservation
of scenery and nature (Pauwels and Gulinck, 2000; Cannarella
and Piccioni, 2005).
The transportation and mainly road safety is one of important issues for Islamic
Republic of Irans planners. The main reasons of this aims are high degree of
urbanization (about 65%), large mountainous land area, the long distances between
large cities and its privileged location at the crossroads of international
trade routes. Islamic Republic of Iran enjoys a well developed transport network.
It has about 81000 km of main and regional roads (95% paved), 7,265 km of railway
lines, four main ports on the Persian Gulf and three on the Caspian Sea and
seven international airports (Zekavat, 2006). The total
length of rural roads in Iran is 86200 km. Terrene roads are widely distributed
in rural areas of the North of IR-Iran. However, the lack of high level design
standards for such roads has led to serious problems in soil and water erosion
(Cao et al., 2006).
The purpose of road surfaces is to provide a relatively smooth and uniform
riding surface with sufficient traction for acceleration and stopping. The surface
should be free of defects and function in all weather conditions. Some types
of road surface deformation affect only the surface layer. Soil cracking and
shallow rutting are limited to the surfacing material and do not penetrate into
the base course. Ruts more than 15 cm deep can indicate more serious problems
with the base and subgrade and the road surface should be reshaped as soon as
possible if it has ruts of between 5 and 12 cm. Five centimeter ruts are easy
to see and are sufficiently deep to carry a potentially damaging amount of water
(Eliasson, 2005; Park et
al., 2003; Hosseini and Jalilvand, 2007).
Initial road failure in our study area was indicated when the drivers complained
about pot holes, surface rutting and roughness. Road surface deterioration increases
driver fatigue, limits vehicle speed, reduces vehicle load capacity and accelerates
vehicle maintenance requirements. In the transportation cost model used today
in rural areas, the only road surface parameter is rut depth and only ruts deeper
than 10 mm are considered to have any influence on traffic safety (Crossleya
et al., 2001). The relation is then linear and transportation cost increases
with increasing rut depth. Rural roads in Denji kola village have three types
of surfacing layer which distinguishes it from other rural roads in region.
Ruts on the surfaces of these roads are different in frequently, shape, width,
depth and length according to geographical aspects, longitudinal gradient and
From a road engineers point of view, it may be helpful to analyze the
deformed terrene roadbed structure based on various theoretical models
and numerical calculations and apply these to a specified regional road
condition. The objective of this research is to evaluate the factors affecting
the deformation of the surface of rural road based on deep wheel rutting
and shallow wheel rutting.
MATERIALS AND METHODS
Study area: The study was carried out in the Denji Kola Village
in Ghaem Shahr City (36° 21 to 36° 38 N and 52° 43 to 53°
3 E), Mazandaran Province, Iran (Fig. 1). Average annual
precipitation and temperature in this area are 724.9 mm and 16.7°C,
respectively. Elevation at see level ranges from 64 to 98 m. During the
rainy season months, the bare soil of the terrene rural roads in present study area become waterlogged and impassible, because there are little
or no facilities for surface or subsurface drainage. During the dry season
months, dust raised by the wheels of passing vehicles becomes a major
environmental and health hazard.
The rural roads were under traffic by different types of machines in
sandy clay loam soil. The mean of Shrinkage Limit (SL), Plastic Limit
(PL) and Liquid Limit (LL) of soil in road bed were 6, 35 and 53%, respectively.
Also, the average of soil bulk density and moisture content in rural roads
were about 1.64 g cm-3 and 19%, respectively.
The ruts depth is correlated with wheel sinkage. Based on the rigid wheel theory,
the rolling resistance coefficient (μR) depends on the wheel
sinkage (z) and diameter (d) (Eq. 1). If, as assumed, the
rut depth is equal to or linearly correlated with sinkage we can write the Eq.
2 for rut depth (ZRUT) where, x is an empirical scale factor
(Saarilahti and Anttila, 1999) (Fig. 2).
Data collection: The total length of rural road in Denji Kola
village was investigated by field study. Deformation of the surface of
rural road was divided in two classes. Class 1 was deep ruts and class
2 was shallow ruts (Fig. 3). The dimensions (width,
depth and length) of all ruts were measured by metal meter and the longitudinal
gradient at the place of each rut was taken by inclinometer.
gradient was divided in three classes 0-4, 4-8 and 8-12%. In addition,
the slope aspect was classified in to Western, Eastern, Northern and Southern.
The traffic condition and maintenance operations were same for all treatments.
Due to the high cost of paved roads a variety of unpaved road surface
types are used. The surface of rural road in study area had three types
of surfacing layers which were including bare soil roadbed, gravel-grassed
roadbed and graveled roadbed. These roads require a much lower capital
expenditure for construction but rely on ongoing regular maintenance to
provide a functioning surface.
|| Calculation of the tire pressure on road surface
||Deformation classifying on rural road surface (a) shallow
wheel ruts and (b) deep wheel ruts
Statistical analysis: Analysis of variance was conducted using
GLM procedures in SAS statistical programming software, respectively.
Means were compared using Tukeys multiple group mean comparison test.
Level of significance used in all results was p<0.05.
RESULTS AND DISCUSSION
Effect of the longitudinal gradient of rural road on wheel rutting:
Rural roads across north of Iran are inadequate in coverage and quality. They
are also usually poorly maintained and therefore poorly served by low-cost,
high-volume transportation providers. An inadequate road infrastructure imposes
significant burdens on rural road maintenance cost. Also, Farmers are faced
with high farm-to-market access costs under unsuitable road condition (Raper
et al., 1995; Obare et al., 2003).
The minor rural road network in northern rural of Iran is an important part
of the landscape structure. It sustains all agricultural activities by connecting
farms, gardens and fields.
Results of this study showed that the ruts length (p<0.0001) and ruts
area (p<0.0001) were significantly affected by longitudinal gradient
of rural roads. There was not significant difference between the mean
of ruts depth (p = 0.153) in different classes of longitudinal gradient
(Table 1). This subject was also observed for ruts width
(p = 0.594). Ruts length in longitudinal gradient class 8-12% was significantly
more than other classes (p<0.05). The mean of ruts length in this class
was 8.19 m (Fig. 4).
|| Analysis of variance for the effect of longitudinal
gradient of road on wheel rutting
|***Significant at probability level of 0.1 %, ns: Not
Comparison of rut lengths in different classes of longitudinal
gradient (different letter(s) show same groups according to Tukey
test at p<0.05)
Comparison of rut areas in different classes of longitudinal
gradient (different letter(s) show same groups according to Tukey
test at p<0.05)
|| Comparison of deep and shallow rut numbers in different
classes of longitudinal gradient
The mean of ruts area in longitudinal gradient class 8-12% was significantly
(p<0.05) more than other classes (Fig. 5). Also,
the number of deep wheel ruts in class 0-4% was more than shallow wheel
ruts, whereas the number of shallow wheel ruts was more than deep wheel
ruts in other classes (Fig. 6).
Effect of the geographical aspect of rural road on wheel rutting: The
analysis of the wheel load of a moving vehicle as well as the measurement of
soil mechanical properties is of great importance for the basic investigation
of wheel-soil interaction, tire characteristics as well as for the input and
validation of vehicle dynamic simulations (Nguyen et al.,
2008). In this study, the effect of geographical aspect did not significantly
influence on ruts depth changes (p = 0.305), but the effects of the geographical
aspect on ruts length (p<0.0001), ruts width (p = 0.0019) and ruts area (p<0.0001)
was significant (Table 2).
The mean of ruts depth in eastern and southern aspects was significantly
(p<0.05) more than other aspects (Fig. 7a). The
ruts in northern aspect of rural road were significantly (p<0.05) longer
than other aspects (Fig. 7b), but the ruts width in
this aspect were significantly (p<0.05) less than southern, western
and eastern aspects (Fig. 7c). Also, the area of ruts
in northern aspect was significantly (p<0.05) higher than other aspects
Effect of the surfacing layer of rural road on wheel rutting: Different
types of surfacing layer in rural roads had significant effect on ruts
width (p<0.0001). The ruts depth (p = 0.096), ruts length (p = 0.297)
and ruts area (p = 0.272) were not significantly affected by different
types of surfacing layer (Table 3).
(a) Comparison of ruts depth (b) ruts length (c) ruts
width (d) and ruts areas in different geographical aspects of rural
road (different letter(s) show same groups according to Tukey test
|| Comparison of ruts width in different types of surfacing
||Analysis of variance for the effect of geographical
aspect on wheel rutting
|**, ***Significant at probability level 0.1 and 1.9%,
respectively, ns: Not significant
|| Analysis of variance for the effect of the type of
surfacing layer on wheel rutting
|*** Significant at probability level of 0.1 %; ns: Not
The mean of ruts
width and ruts depth in gravel-grassed surface was significantly (p<0.05)
more than other surfacing layers (Fig. 8). Bare soil
had lowest rut width and depth (Fig. 9). These ruts
were numerous on bare soil in surfacing layer.
In many European regions, structure and use of the minor rural road network
have been changing rapidly during last decades. Changes in agricultural transport
and a consequent demand for upgraded roads, changes in management of and impacts
on road verges often lower landscape and nature qualities and increase conflicts
between the different user groups of roads and verges (Pauwels
and Gulinck, 2000). Local governments in Eastern European countries also
face problems with budgets for local rural roads. Up to around 1990, the roads
were under the responsibility of the collective farms (Jaarsma
and Willems, 2002).
|| Comparison of ruts depth in different types of surfacing
Rural roads connectivity is one of the key components for rural development,
as it promotes access to economic and social services, generating increased
agricultural income and productive employment, while building rural roads,
the provisions based on the parameters that affect the sustainability
are to be made, but at minimum cost. In most rural areas of the north
of Iran, roads into and out of the citrus gardens are idle before harvest
offering an ideal opportunity to plant grass on the roads as anti-erosion
measure. The longitudinal gradient of rural roads must be reduced, because
in steep sections of road the ruts length and consequently water erosion
increases. Although, the ruts width and depth on gravel-grassed surface
was more than other surfacing layer, the number of ruts in this surfacing
layer was less than bare soil and graveled surfacing layer. Thus, thickness
layer of gravel which has been covered by grass is the best mixture for
surfacing layer of rural roads.