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|Ivica PAPA, Tibor PENTEK, Hrvoje NEVEČEREL, Kruno LEPOGLAVEC, Andreja ĐUKA, Branimir ŠAFRAN, Stjepan RISOVIĆ||UDK 630* 383 +386 (001)|
|THE ANALYSIS OF THE TECHNICAL FEATURES AND DRAINAGE SYSTEM FOR EXISTING FOREST ROADS IN ORDER TO ESTABLISH THE NEEDS OF THEIR RECONSTRUCTION – A CASE STUDY pdf HR EN||497|
Technical features of forest roads in the Republic of Croatia are presented in Technical Conditions for Economic Roads (Šikić et al., 1989). Pentek et al. (2007) gave a proposal of new technical conditions in which the basic criterion of categorization of forest roads is traffic load. According to the Regulations (Anon. 2015), in Annex IV. “Technical conditions of forest roads”, the proposal of improvements to the existing Technical Conditions for Economic Roads is accepted (Šikić et al., 1989) (Table 1).
The objectives of the research are: 1. Measurement and analysis of selected technical features of forest roads and comparison with the current technical conditions in the Republic of Croatia (Šikić et al., 1989; Anon, 2015), 2. Recording and analysis of ground and underground drainage elements; road facilities and assessment of construction material categories and 3) Definition of technological process for reconstruction of forest roads in order to achieve current technical conditions and optimization of drainage systems (“zero”/optimal state).
In the field, in the framework of the establishment of a detailed registry of primary forest traffic infrastructure, for each of the seven forest roads in MU “Belevine”, on each sampling plot of 20.00 m length, according to a newly developed methodology for the establishment of a detailed registry of primary forest traffic infrastructure (Papa et al. 2015), were measured/calculated the following selected technical features: pavement width, shoulder width, longitudinal alignment gradient and pavement cross fall slope (Figure 3 and 4).
Forest roads “587 B1 001”, “587 B1 004” and “587 B1 006” were, according to the criterion of Šikić et al. (1989), categorized as main forest roads, forest roads “587 B2 002”, “587 B2 003”and “587 B2 007” belong to the category of side forest roads and forest road “587 B3 005” is an access forest road (Figure 5). Due to the traffic characteristics on mentioned forest roads, characteristics of MU “Belevine” and of forest stands, it would not be justified to construct forest roads with two lanes; therefore on forest roads „587 B1 001“, „587 B1 004“ and „587 B1 006“ will apply technical specifications that apply to side forest roads, and for other forest road technical characteristics that are valid for the category of access forest roads.
As a minimum width of pavement for the category of side forest roads reference value will be 4.00 m, and for the category of access forest roads 3.50 m. Side forest road minimum width of shoulders is 0.75 m and for the access forest road is 0 50 m. Maximum longitudinal alignment gradient for side forest roads is 10%, and for the access forest roads 12%. The minimum permitted vertical alignment gradient for all categories of forest roads is 0.50%. The minimum value of pavement cross fall slope for side and access macadam forest roads amounts to 3%, and the maximum permitted value of 6%.
For each component of the primary forest traffic infrastructure in MU “Belevine”, by measuring surfaces, the spatial distribution and the current state of elements of the ground and underground drainage: drainage ditch, culverts, bridges, cross ditches and fords was recorded. The position of all road facilities and other elements of forest roads were recorded. For each sampling plot, according to the schematic representation in Figure 2, the basic components of four transverse sections at a distance of 5.00 m were recorded. The cross-sections were evaluated according to material categories. In assessing the current state of the elements of ground and underground drainage, road facilities and other elements of forest roads, used methodology developed within the whole methodology of a detailed registry of primary forest traffic infrastructure is shown in Table 2 (Papa et al. 2015).
Studies have been conducted on the components of the primary forest traffic infrastructure in MU “Belevine” within the Training and Research Forest Centre Zalesina, Faculty of Forestry, University of Zagreb. Seven macadam forest roads, of the total length 7.031 kilometers, were built in the period from 1968 to 1988. From construction to the present day, all the forest roads were regularly maintained, and maintenance was predominantly focused on repairing damages of road construction and drainage facilities.
Figures 6, 7, 8 and 9 are show the analysis of variance of measured and reference (prescribed) values for each selected technical features of forest roads. For two longest forest roads in MU “Belevine”, “587 B1 001” length 2207.48 m and “587 B1 004” length 2046.62 m, a comparison of selected current technical features to prescribed values of the same features of the Republic of Croatia (Anon, 2015) for each sampling plot (Figure 10 and 11) was done. All the selected technical features of forest roads in MU “Belevine”, to a lesser or greater extent, deviate from the prescribed/reference values. It is interesting to note that all forest roads categorized as side and access (with the necessary technical features of the side forest roads) have a higher mean value of the pavement width than those categorized as main roads (with the necessary technical features of the access forest roads). This is explained by the dynamics of the primary forest opening of the study area. The forest road “587 B1 001” and “587 B1 004” are the first forest roads built in MU “Belevine”, in time of less developed construction technology, different technical characteristics of forest transport vehicles and during the validity of different technical requirements for forest roads.
The smallest permitted vertical alignment gradient is not a problem at any of the sampling plots of the researched forest roads. The maximum longitudinal gradients were recorded only on shorter sections of forest roads and values were slightly higher than allowed, or in the framework of exceptional justified cases which in the technical documentation must be explained in detail (in hilly/mountainous area for side forest roads up to 12%, and for access forest roads up to 15%). The reported values for pavement cross-slope values were unsatisfactory on most of the sampling plots. Reconstruction of pavement cross fall slope should lead to optimal state (between 3 and 6% for the access and side forest macadam roads).
The spatial distribution and the existing state of the ground and underground drainage system elements on sampling plots of primary forest traffic infrastructure is shown in Figure 12. Table 3 shows first at the level of individual forest road and then at the level of entire management unit integrated information about ground and underground drainage system elements. There is no forest road on which intervention in the objects of ground and underground drainage system elements (in terms of enabling them to be fully functional) is unnecessary.
For the ground drainage system to be optimized, the total of 3520 m classic and 1680 m lined drainage ditches on seven forest roads in MU “Belevine” should be constructed, as well 860 m classic drainage ditches, of which 240 m translated into lined drainage ditches should be repaired. It is necessary to construct 47 new and repair 41 existing cross-ditches. 45 concrete pipe culverts were recorded. With regard to the developed hydrograph conditions close to forest roads, existing climatic and geological features of soil in MU “Belevine”, and with the aim of diminishing/reduce the negative impact of water on forest roads, pipe-culverts, drainage ditches and cross-ditches of the right shape, size, and type should be constructed. The elements of an optimized system of ground and underground drainage, along forest roads as well as and for the entire MU “Belevine” are given in Table 5.
Damaged road construction and the proposed method of repairing macadam pavement structure at the level of individual forest roads and for the entire MU “Belevine”, are shown in Table 6. Macadam pavement structure of forest roads is in good condition and does not require any intervention on 4.01% of sampling plots. At 23.98% of sampling plots, pavement can be repaired with mending method. Most of sampling plots (51.40%) show that repair pavement method should be aligning, and for 20.62% of sampling plots the most expensive method of pavement repair – material outspreading is necessary.
In future studies it is recommended that to the technological process of reconstruction of forest road network in MU “Belevine”, and it is bringing to so-called “zero”/optimized state, analysis of associated costs should be included.
Key words: forest road; technical features; drainage system; reconstruction of forest roads; mountainous relief area
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