5.1 GENERAL
5.2 STAKING, FELLING, FORMING, CLEARING AND MISCELLANEOUS WORK3
5.3 GRAVELLING
Machine costs in mechanized forest road construction may easily amount to 80 to 90 percent of the total road costs, thus construction activities must be carefully planned so that the equipment is used as efficiently as possible and thus idle time of the machines is minimized.
The skill of the forest engineer who does the road location and design is critical to the overall construction costs.
Road construction costs may vary considerably depending mainly on the terrain and soil conditions, road standards, machine and labour costs, etc., as well as on the skill of operators and labourers involved. However, since road construction techniques are similar throughout the world, one can easily derive reasonable cost estimates once the main conditioning factors have been identified, by applying figures from similar road construction projects.
For the purpose of facilitating your task in estimating forest road costs and for reasons of comparing costs, it is advisable to break down labour and machine costs into their different elements.
The following breakdown is suggested:
(i) Surveying, staking the alignment and clearing right of way(ii) Formation of the road
(iii) Rock blasting
(iv) Drainage facilities (ditching, culverts)
(v) Crushing gravel
(vi) Gravelling, grading and compacting
(vii) Construction and environment protection works (bridges, retaining structures and soil stabilization works). The cost of construction of these is not dealt with in this paper.
(viii) Miscellaneous work (such as transport, delivery and minor earth works)
(ix) Project servicing costs
Once the costs have been calculated for the different elements, unit costs (costs per m, per m3, per piece of construction work) should be developed to facilitate in estimating costs in future road projects and for comparative purposes.
3 Miscellaneous work such as construction of sub-base culverts and road-side drains.
In the case of a complete absence of costs data for forest road construction in tropical countries, FAO has developed a cost formula applicable to four different road standards and slopes, comprising the following work elements: felling; forming; clearing; grading and miscellaneous work. These work elements represent a major share of the total road costs.
The equation reads as follows:
C1= 370+(27xSL)+(1050xSTi)+(48xSLxSTi)
Where C1 is the direct cost in US$ per km for road standard i (supervision and overheads excluded), and where i is one of the four standards given in Table 3.
SL -the inclination in percent of the major slopes (slopes longer than 50 m) of the hillsideSti -the values of the four road standards as taken from Table 3, i.e.
O -for trails for wheel skidders and jeeps
1 -for secondary feeder roads
2 -for primary feeder roads
3 -for main and access roads
The cost formula gives costs in US$ as at 1977 and would need to be adjusted taking into consideration inflationary cost rises in recent years. The formula applies for the following road widths including shoulders as shown in Table 3.
TABLE 3
Values used for Different Road Standards
|
Standard |
Description |
Road Width |
Value (Sti) |
|
1 |
Access roads and main primary roads |
10 to 12 m |
3 |
|
2 |
Primary feeder roads |
8 to 10 m |
2 |
|
3 |
Secondary feeder roads |
5 to 7 m |
1 |
|
4 |
Skid trails |
3.5 to 4.5 m |
0 |
It should once again be mentioned that this formula can only serve as an approximation in a road construction estimate for the elements mentioned and it is not applicable at all for costing of ridge roads.
Example: direct construction costs should be calculated with the above mentioned equation, making the following assumptions. Required is a secondary feeder road on a 30% slope. The equation then reads:
C3 = 370 +(27 x 30 +1050) x 1 + (48 x 30 x 1) = 3 670 US$
Thus, direct construction costs for the above road standard would amount to about US$3 670. (the actual costs in the area under review should be used).
On soils with low bearing capacity, gravelling is required to increase the load bearing capacity of the road and make it useable by heavy duty vehicles on a year-round basis. Depending on the carrying capacity of the ground (underlying soils), the road width and the availability of appropriate gravel material, including its transport costs, gravel costs can rise up to 60 percent of the total costs and so become the most expensive item. Sometimes the non-availability or availability from far-distant sources of gravel in certain forest areas can be large factors in determining the viability or non-viability of forest projects.
For easy reference an example of gravel costs from a developing country is given when considering the following work inputs: taking the road material from a natural gravel pit, transporting, spreading and compacting it. When considering a 4 m wide road with 25 cm of gravel thickness, costs would also apply per m forest road.
TABLE 4
Estimated Costs of Gravelling a Forest Road from a Natural Gravel Pit
|
Item_Cost in US$/m3 4 |
|
|
Natural gravel at the pit |
0.15-0.60 |
|
Loading of small quantities |
1.10-2.10 |
|
Loading of large quantities |
0.25-0.45 |
|
Transportation |
1.70 per m3 plus |
|
Grading |
0.20-0.30 |
|
Rolling |
0.30 -0.40 |
4 Estimated costs expressed in US $/m3 as at 1980.
When transporting gravel over a distance of 10 km the total gravel costs per km may amount to US$4.70 to US$6.55 per m3 placed on the forest road, thus the cost of a 25 cm thickly gravelled 4 m wide forest road would be US$4 700 to US$6 550.
