journal of forest science

Table 1. Coefficients of regression equation and basic statistical characteristics for individual experimental sections
No. Experimental sections
Section
Coefficients
of regression equation
Square deviation Residual variance Correlation index
A0 A1 A2 1 Hlboká 0.871 0.021 0.002 0.011 0.011 0.96
2 Bujaèie 0.388 0.062 – 0.272 0.045 0.79
3 Žiarkov 0.512 0.124 –0.006 0.002 0.001 0.99
4 Huèava III 1.673 0.042 – 0.186 0.047 0.65
5 Huèava IV 1.703 –0.015 –0.050 –0.015 0.018 0.93
6 Huèava V 0.697 0.156 –0.002 0.309 0.051 0.93
ciency (bearing capacity) of roadways in forest roads.
The other parameters such as roughness, evenness (longitudinal
and square) were not investigated (unlike the
public roads) because these parameters are considered as
complementary. It is so because the average speed of vehicles
on forest roads is 18 km/h.
The course of roadway degradation was evaluated by
measuring changes in the deflection value with a diagnostic
equipment, arm deflectometer. Roadways were
also evaluated visually, mainly the surface condition of
the roadway (occurrence of pot-holes and cracks and
other damage). The roadway deflection was measured
every year in the spring season (after subsoil defreezing).
The deflection method was already described in another
paper (ZELINKA 1981). The reversible roadway
deflection was measured under different temperatures,
the measurement points were determined by random selection
at an average distance 30 m, the length of the investigated
sections was 300 m or more. The data were
processed by computing technique.
RESULTS AND DISCUSSION
The roadway degradation was investigated on 22 experimental
sections. The results of monitoring on 6 experimental
sections are published in this article. The
following roads are represented by these sections:
– old gravel forest road paved with OK (covered bituminous
stone),
– old forest road with PAH surface (penetration bituminous
macadam) paved with 10 cm OK,
– new forest road with PAH and OK surfaces.
Each figure represents:
– course of deflection changes during the time of forest
road (section) use (observation),
– operating performance expressed by the number of
standard axles (ŠN) for 24 h,
– total quantity of timber hauled during the time of roadway
use expressed by the number of ŠN.
Note: The roadway operating performance was determined
by the method for testing and pavement which was
already described in detail (ZELINKA 1989).
SHORT STATISTICAL EVALUATION
By monitoring the roadway degradation non-linear
correlations – polynomial of degree II were found in most
cases on the basis of deflection changes (increase in deflection)
within the file. Linear correlations were determined
in a smaller number of experimental sections.
All sections presented in this article show non-linear
correlations except the experimental section situated on
Bujaèie forest road where a linear correlation was found.
General relation for:
– linear correlation: Y = A + A . x 0 1 1
– non-linear correlation: Y = A 0 + A 1 . x 1 + A 2 . x 2
where: Y – roadway deflection,
x – time of roadway use in years,
A 0 , A 1 , A 2 – regression coefficients.
The basic statistical characteristics for individual experimental
sections are shown in Table 1.
Experimental section on Hlboká forest road (ig. 1)
This experimental section is situated on an old, gravel
forest road (25cm layer of broken stone) which was paved
with 12cm layer of OK (covered bituminous stone). The
measurement of deflection began 14 days after overlay.
The graph shows a moderate increase in deflection in
time, that means roadway gradual degradation. At the beginning
of pavement the operating performance of roadway
was 100 ŠN/24 h, after 5 years it was 60 ŠN/24 h,
after another 5 years it was 28 ŠN/24 h. It is assumed that
after another 8 years, i.e. after 15 years of operation, the
operating performance will achieve the value 5 ŠN/24 h.
The average wheel traffic on this roadway does not
exceed 1 SA/24 h, so there is some reserve before the
limiting condition of the roadway is reached. (Note: the
limiting condition of the roadway is a state when the
wheel traffic does not yet cause either qualitative decrease
or loss of bearing capacity, that means total and
irreparable damage of the roadway by destruction.) It can
be stated by visual evaluation of the roadway that the
roadway is not damaged by wheel traffic for the time
being. This road is damaged (pot-holes and other damage
of the surface) on other parts than on the experimental
section and the damage is caused mechanically
(skidding, excavations).
Experimental sections on Bujaèie – Trnavy forest
road (ig. 2)
These experimental sections are situated on an old forest
road (constructed in about 1941–1942) which was
gradually paved. The primary gravel roadway was paved
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J. FOR. SCI., 47, 2001 (7): 314–321
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