0460-B4
Ress. Assist. Habip EROGLU, Hulusi Acar, Mehemt Eker 1
The forest road superstructure has occurred from pavement, under pavement, base, and sub-base layers. Because the road superstructure is located on natural ground, it is affected physical structures of sub-grade. To obtain the suitable ground for forest road construction, road sub-grade is investigated geological aspects by using of technological possibilities. After determining of the appropriate road sub-grade, sub-base, base and pavement layers are constructed as a suitable size and structure. In this phase, various techniques and materials are used for improvement of the road ground.
The forest roads are exposed to excessive load during wood transportation realized by heavy trucks. This excessive loads effect as negative to forest roads with together environmental and natural impacts as well. For this reason, the selection of suitable ground, where are constructed the forest roads, should be done according to terrestrial attributes for soil stabilization and the forest roads should be immediately reached to superstructures.
In this study, the various techniques, materials and stabilizers used on stabilization, improvement and pavement of forest roads, were examined. In addition that, the actual situation of the road superstructure was exposed and it was discussed and evaluated which stabilization and pavement technologies are appropriate to Turkish forest roads.
The forest roads are deteriorated because of excessive load, transportation on negative weather condition, inconvenient drainage construction, planning the forest roads on low bearing capacity soils, using of unsuitable techniques for forest road construction. Damages of forest road increase the cost of maintenance of forest roads. To decreasing the damages of forest road surveys, the wood transport should be realized on dry season and forest road survey should be stabilized with the additive materials.
It is called as the stabilization that soil improvements constituted with chemical and physical methods to prevent mechanical and climatic deformation to be occurred on superstructure (roadbase, sub-base and subgrade) of the road. Aside from conventional methods of soil stabilization, there are also modern methods of soil stabilization can be put into practiced by chemical materials and organic enzyme like successfully applied in the forest road. Geosynthetics and chemical products like that geotextiles, RRP, WEGS, Perma-zyme, and industrial waste (such as fly ash) are used for soil stabilization The stabilization methods practiced with these products, caused to promote bearing capacity of forest roads.
Low-volume forest roads are typically constructed with native materials using basic earthmoving machinery. The resulting roads typically have low bearing capacity and develop ruts under traffic, particularly during wet weather. Aggregate is often applied to provide additional bearing capacity and as a wear surface. During use, frequent regarding is often necessary to maintain a usable road surface (USDA, 2000).
Stabilization of forest roads started in its primitive from since ancient times. The need for stabilization of forest roads became obvious in central European forestry in the last two centuries due to adverse soil and climatic condition for forest operations. The first approach took place 50 years ago and the principal materials that have been used for stabilization included lime, lime-flay ash and lime-NaCl mixtures, portland cement and RRP-235 (Eskioglou and Efthymiou, 1996).
In the recent years, researchers from many fields have attempted to solve the problems posed by industrial wastes. Finding a way for the utilization of these wastes would be an advantageous way of getting free of them. Recent projects illustrated that successful waste utilization could result in considerable savings in construction costs (Kamon and Nontananandh, 1991 and Cokca, 1999).
Fly ash being the most common pozzolanic material encountered in construction is a by-product of coal burning power plants. The fly ash is disposed of either by sluicing to ponds or hauling to solid waste disposal areas. Disposal operations are quite expensive and require the use of land that could be used for other purposes (Parker et al, 1977 and Cokca, 1999).
Design of superstructures for forest roads involves the same principles used for any roadway except that traffic volumes are less and frequently the distribution of vehicle types is considerably different. Forest roads may be public highways or private roads limited primarily to hauling of timber, ore, or other products. Axle loadings on public highways are designed for heavy loads, which are legally limited although not always rigidly enforced, but primitive roads may be designed for loads twice those legally allowed on highways (Ericson 1975).
The designing of super structure is based primarily on;
The component layers of the superstructure of are shown in the following figure (Figure 1).
Figure 1. Definition of superstructure layers (Overseas Road Note 31, 1993).
In this study, forest road stabilization with lime and cement was explained because cement and lime for forest road stabilization and these materials are produced abundantly in Turkey. Besides, forest road design process and actual situation for forest roads aspect for superstructure in Turkish forestry was exposed.
There are three main steps to be followed in designing a new road superstructure. These are;
The overall process of designing a road is illustrated in Figure 2.
Figure 2. The pavement design process (Overseas Road Note 31, 1993).
The various soil additives were developed to provide one of the following function when added to soil; improve soil strength, soil aggregate stability and water infiltration, and to limit water adsorption, soil erosion, evaporation of moisture and water seepage (Brandt, 1972). As a result many types of soil additives or modifiers were formulated depending on the end application of these additives (Shawqui, Neaz, 1998).
Stabilization can be enhancing the properties of road materials and pavement layers in the following ways;
Associated with these desirable qualities are several possible problems;
The minimum acceptable strength of a stabilized material depends on its position in the pavement structure and the level of traffic. It must be sufficiently strong to resist traffic stresses but upper limits of strength are usually set to minimize the risk of reflection cracking.
The selection of the stabilizer is based on the plasticity and particle size distribution of the material to be treated. The appropriate stabilizer can be selected according to the criteria shown in Table 1, adapted from NAASRA (1986).
Table 1. Guide to the type of stabilization likely to be effective (Overseas Road Note31,1993).
Type of stabilization |
Soil Properties | |||||
More than 25% passing the |
Less than 25% passing the 0.075 mm sieve | |||||
PI ≤ 10 |
10 ≤ PI ≤ 20 |
PI>20 |
PI ≤ 6 |
PI ≤ 10 |
PI>10 | |
Cement |
Yes |
Yes |
* |
Yes |
Yes |
Yes |
| Notes 1. * Indicates that the agent will have marginal effectiveness 2. PP = Plasticity Product, PI= Plasticity Index |
Some control over the grading can be achieved by limiting the coefficient of uniformity to a minimum value of 5. The coefficient of uniformity is defined as the ratio of the sieve size trough which 60 percent of the material passes to the sieve size through which 10 percent passes. If the plasticity of the soil is high there are usually sufficient reactive clay minerals, which can be readily stabilized with lime. Cement is more difficult to mix intimately with plastic materials but pre-treating the soil with approximately 2 percent of lime to make it more workable can alleviate this problem.
Stabilization of soil with cement can be used for all soils except from organic soils. Proportion and plasticity of clay, dust, and silt constitute technical and economic limit. In high plasticity (PI > 15), where mixing it so hardly that its expenditures exceed the economical standards. The more slim fractions increase, the more required cement quantity increase to stabilization. In that case, to raise stability required dosage got to over 10%.
The cement content determines whether the characteristics of the mixture are dominated by properties of the original soil or by the hydration products. As the proportion of cement in the mixture increases, so the strength increases. Strength also increases with time. During the first one or two days after construction this increase is rapid. Thereafter, the rate slows down although strength gain continues provided the layer is well cured. The choice of cement content depends on the strength required, the durability of the mixture, and the soundness of the aggregate.
When lime is added to a plastic material, it first flocculates the clay and substantially reduced the plasticity index. This reduction of plasticity is time dependent during the initial weeks, and has the effect of increasing the optimum moisture content and decreasing the maximum dry density in compaction. The compaction characteristics are therefore constantly changing with time and delays in compaction cause reductions in density and consequential reductions in strength and durability. The workability of the soil also improves as the soil becomes more friable.
Both the ion exchange reaction and the production of cementations materials increase the stability and reduce the volume change within the clay fraction. It is not unusual for the swell to be reduced from 7 or 8 percent to 0.1 percent by the addition of lime. The ion exchange reaction occurs quickly and can increase the CBR of clayey materials by a factor of two or three.
The most common form of commercial lime used in lime stabilization is hydrated high lime, Ca(OH)2, but monohydrated dolomitic lime, Ca(OH)2, MgO, calcitic quick lime, CaO, and dolomitic quicklime, CaO, MgO are also used.
In Turkey, there is 201 810 km forest road planned to construction. By end of 2000, 71.4 percent (144 091 km) of the planned was constructed. Superstructure was realized in section 28 442 km (19,74 percent) of forest road of which was completed their construction (SPO, 2001).
Because the forest roads of Turkey were constructed for purposes of harvesting, it is abstained from high cost of the forest road constructions. For the reasons, most of the forest roads are earth road, where except for mechanical stabilization, another else stabilization methods of soil improvement have not practiced, yet. Although stabilization with cement and lime is known, these have not used for forest road so far. So that can be used these stabilization techniques, assuring or providing these materials and experienced personnel are required.
Since forests of Turkey are operated related to harvesting functions and strategically and tactical planning of the forests is prepared to this purpose, economic criterions are only taken into consideration for the forest road constructions. Now, mechanical stabilization techniques applying more primitive than have been known.
The mechanical stabilization process contains following treatments; taking into consideration distance to the forest road network has chosen stone quarries. Confidence of materials is obtained from current a section of cut slopes where rock fragment is broken into small pieces. Without drill and stone crusher are required, the excavated materials are carried out by single axle dump truck, through cross line of the forest road and they are unloaded to somewhere. Using of stabilization materials for soil improvements have increased in the crossing stream where overflow of underground water (Acar and Eker, 2001).
The materials necessary to stabilization of forest road are sprawled by operator of grader, one instructor, and several road employers. In addition to this, excavating materials from roadside are used exactly same as without washing, eliminating or crushing for improvement of granular and technical components. The materials sprawled out to road surface are compressed with the forward and backwards movement of grader and other equipments.
It is not important that size of materials been spread out to road surface. Average sizes over 35 cm materials are separated with handle or knife of grader. After that, road surface is leveled. Movement of grader, loader or bulldozer realizes mechanic compression. Also traffic accesses undertaken compressive function for stiffness of stabilized layer after opening-up of forest roads.
In the methods of mechanical stabilization, although the materials to be sprawled out to road surface for stabilization is requested to increasing of aggregation, given up this treatment to decline of construction cost. Another technique of stabilization is improvement of granulation. For the purpose, either gravel is carried out from suitable wherever, or existing materials are treated with respect to its technology in order to be stabilization. So that existing materials can be used in the stabilization, some machines are necessary to be washing, crushing, and eliminating them.
Constructing roads according to an engineered design is the considerable way to assure that roads are environmentally acceptable, economically feasible, and physically possible to meet the demands for which they are built.
Plastic soils can be successfully improved after stabilization with lime and cement. The treatment of very plastic clays with lime leads to a decrease of liquid limit, which is increased in the less plastic ones. Stabilization of roughly structured soils with cement changes the soil Atterberg limits to a minor degree but it improves more the strength, compared to lime stabilized.
The forestry operations cause to deformation on the forest ecosystem and forest road. Both forest vehicle carrying out wood or personal and forest tractor and skidders cause to compress and deformation on the forest soil and road. In the soils where forest road is built, is shown difference point of view structure and humidity. Traffic loading, tire pressure, tire volume and soil type are very important for deformation of forest road. Stabilization is necessary to prevent forest roads from wind, water erosion, tire pressure and so that it can be served in long period.
The forest roads, which is placed mountainous areas and humid climatic zones, have deformed, and traffic running has been frequently exposed to interruption especially in wet period. It is suffered from subject that erosion happening in the surface of forest roads and flowing of fill slope not to be stabilized from environmentally soundly point of view. In case of by combined with mechanical and chemical methods of soil stabilization to apply in the forest roads, problems of soil stabilization can be removed.
Forest roads should be designed and constructed considering the following points; location of wood, volume and assortment to be annually transported, as well as management purposes; natural conditions of relief, soil structure and geophysical characteristics of the land; economic conditions and costs required for rod construction, maintenance and operation; possibilities of mechanized operations structure and forest operations period.
According to determined kind of soil stabilization method and existing materials and machines, a process of stabilization should be followed. For the modern stabilization methods chemical products should be imported and produced to use. These materials should be compared with each other and the most economic and suitable is chosen for the forest road of Turkey.
Acar, H.H., Eker, M., 2001. New Improvements on Techniques of Forest Road Stabilization and Situation In Turkey, Proceeding of I. National Forestry Congress, 19-20 March, Ankara.
Brandt G.H., 1972. Soil Physical property modifiers, In; Gorning CAI, Hamaker JW, editors. Organic Chemicals in the Soil Environment, Marcel Decker, 2, p.692-729.
Cokca, E., 1999. Effect of Fly Ash on Swell Pressure of an Expansive Soil, The Electronic Journal of Geotecnical Engineering Vol. 4.
Erickson L.F., 1975 Low-Volume Road Pavements, Low-Volume Roads, Special Report 160, Transportation Research Board, National Research Council, National Academy of Sciences, Washington.
Eskioglou, P., Efthymiou, P.N., 1996. Alternative Stabilization Methods of Forest Roads For An Effect and Gentle Mechanization of Wood Harvesting Systems. Proceedings of the Seminar on Environmentally Forest Roads and Wood Transport, 17-22 June, Romania
Kamon, M., and Nontananandh, S., 1991Combining industrial wastes with lime for soil stabilization, Journal of Geotechnical Engineering, 117, p.1-17.
National Association of Australian State Road Authorities, 1986. Guide to stabilization in roadworks. NAASRA, Sydney.
Overseas Road Note 31, 1993. A guide to the structural design of bitumen-surfaced roads in tropical and sub-tropical countries, Overseas Centre, Transport Research Laboratory, Crowthorne, Berkshire, United Kingdom.
Parker, D.G., Thornton, S.I., and Cheng, C.W., 1977. Permeability of fly ash stabilized soils, Proceeding of the specialty Conference of the Geotechnical Engineering Division of ASCE on Geotechnical Practice for Disposal of Solid Waste Materials, p.63-71.
Salvador S., Pons O., 2000. A semi-mobile flash dryer/calciner unit to manufacture pozzolana from raw clay soils-application to soil stabilization, Construction and Building Materials, 14, 109-117.
Shawqui, M.L., Neaz, A., 1998. Effect of New Soil Stabilizers on the Compressive Strength of Dune Sand, Construction and Building Materials, 12, p.321-328.
SPO-State Planning Organization, 2001. VIII. Five Year Development Plane (2001-2005), Forestry Special Impression Commission Report, State Planning Organization Publication No:2531, Ankara
USDA Forest Service, 2000. Current Project Record 00-01, March 15.
1 Karadeniz Technical University, Faculty of Forestry, 61080, Trabzon-TURKEY, [email protected],
Karadeniz Technical University, Faculty of Forestry, 61080, Trabzon-TURKEY, [email protected],
Karadeniz Technical University, Faculty of Forestry, 61080, Trabzon-TURKEY, [email protected]