journal of forest science

According to the method of model derivation we can
distinguish:
1. mechanical approach – it uses the knowledge and regularities
from mechanics of construction degradation;
2. empirical approach – it uses all knowledge about roadway
degradation obtained empirically;
3. combined mechanical and empirical approaches with
application of theory and practical information.
The roadway properties may be evaluated:
a) in laboratory – by accelerated stress and testing,
b) in real conditions – in a network of roads.
However, the laboratory methods and measurements
are not suitable for an independent empirical method. The
method of degradation model combining mechanical and
empirical approaches is used very often. The results of
laboratory tests of physical properties of the materials
are the basis for evaluation of the construction (degradation)
under accelerated testing for example on a circular
and straight course but especially in a network of roads.
The results from long-term measurements and observations
(LTPP – long-term pavement performance) under
real climatic conditions and wheel traffic are the most
valuable. The relative time reduction to acquire needed
data is possible by selection of suitable localities and
conditions (their combination).
Two types of models are needed as concerns the planning
of roadway maintenance and renewal in the network
of roads:
– degradation models of new roadways,
– degradation models of rehabilitated (renewed) roadways.
We must distinguish the categories of “aggregated” and
“segregated” models according to the fact whether the
model reflects the aggregated evaluation of roadway condition
or if it relates only the changes in a segregated
parameter. The measurements for roadway renewal are
several and therefore the models are “compound-combined”
or “single-specific”.
Degradation models based on aggregated coefficients
– parameters can also be combined with different conditions.
“The network analysers” are used for planning and
roadway renewal in a network of roads as a whole. Other
models are “specific” models for a selected section of
the road with some roadway composition in combination
with the existing conditions on this object – climatic load
and wheel traffic.
or a prognosis of the course of roadway degradation
the models and functions are needed which relate to segregated
or aggregated evaluation of:
– roughness of roadway surface,
– evenness of roadway surface in square and longitudinal
directions,
– mechanical efficiency (bearing capacity) of roadway,
– index of serviceability,
– surface condition, intensity and degree of surface damage,
– index of construction condition as well as other parameters.
To evaluate the roadway condition it is possible to use
two basic evaluation methods:
a) diagnostic evaluation,
b) visual evaluation.
The combination of both methods is used most frequently.
The visual evaluation of roadway surface is generally
primary and it is complemented by diagnostic
evaluation with special equipment.
Degradation models and degradation functions for public
roads in Slovakia are at their beginning for the time
being due to a small number of measurements, they are
in the phase of proposals. They will be based on the results
of measurements on circular experimental roads of
VÚIS – Cesty, s.r.o., Bratislava and the results of visual
evaluations on a highway section D 61. The situation in
the Czech Republic is similar.
The publication of the World Bank contains the prediction
of roadway degradation, degradation models and
functions with description of so-called HDM-III model
(The Highway Design… 1987). There are presented the
empirically determined relations for variable parameters
(cracks, depth of tracks) in dependence on wheel traffic.
These relations are defined for different types of roadway
but their use is limited. The models are not valid for
the conditions of roadway and subsoil frost penetration.
The results of the World Bank relate to public transport
and they are suitable mainly for a public network of roads
with higher wheel traffic.
ERTÁ¾ (1996) dealt with the problem of forest road
damage in Slovakia. He evaluated the main forest roads
with surface from penetration asphalt macadam following
the visual evaluation namely of the occurrence of “the
crack portion” and their increase during use. This author
found that the practical service life of roadway surfaces
and all roadways ends when the value of “the crack portion”
amounts to 4%, that means eight years of roadway
use in Slovak conditions.
The solution to this problem (on forest roads) in foreign
countries is not known from available literature.
MATERIAL AND METHODS
To solve this problem, a long-time monitoring of
changes in the bearing capacity of non-rigid roadways of
forest roads with bituminous surface was carried out. The
research was conducted mainly in the area of the Training
orest Enterprise Zvolen and also in other areas of
Slovakia.
Monitoring of degradation processes on forest roadways
began in 1976, more intensive since 1980. The
roadway degradation is studied in real conditions (directly
on forest roads) under different climatic influences,
wheel traffic and constructional design of the roadway.
The file of the studied roadways comprised new
roadways, old roadways as well as roadways after overlay.
Unlike the public roads where evenness is the basic
criterion for quality evaluation, it is the mechanical effi-
J. FOR. SCI., 47, 2001 (7): 314–321 315