10.1 CLEARING OF THE CONSTRUCTION AREA
10.2 ROAD CONSTRUCTION BY EXCAVATOR
10.3 ROCK DISINTEGRATION
10.4 DESCRIPTION OF THE ROAD CONSTRUCTION EQUIPMENT
10.5 ESTIMATING PRODUCTION AND PERFORMANCE RATES
10.6 ESTIMATING COSTS
10.7 QUALITATIVE ASSESSMENTS OF ENVIRONMENTAL IMPACTS
Environmentally sound forest road construction techniques as holistic, interdisciplinary approaches that take into account the need for landscape and wildlife considerations should replace purely technology-oriented solutions (Litzka & Haslehner, 1995) and are to be guided by the following principal considerations:
· any disturbance to the landscape is to be kept to the absolute minimum;· environmentally sound correction of poorly located and designed roads at a later stage is virtually impossible;
· reckless and incompetent construction work may destroy the beneficial effects of even the most carefully selected road location (layout, alignment);
· undesired effects and scars inflicted on the landscape can seldom be remedied at a later stage and only at much higher costs.
Equal attention is to be paid to the three phases in road construction projects (Litzka & Haslehner, 1995), namely, planning and design, construction operation, and integration which comprises bioengineering as well as landscaping measures. All operations undertaken are guided by the consideration that unless the forest is left in a condition that will permit the attainment of a desired future condition, sustainability cannot be assured (Dykstra & Heinrich, 1996).
The detailed information given focus on construction activities. Some details also refer to integration measures as they are accomplished by means of excavator.
Prior to clearing of the construction area, the design information is to be moved from the plan to the ground by staking. There are a variety of staking methods which can be employed, however, where the gradient rather than the horizontal alignment is the controlling factor, simpler methods of location have been developed (Sedlak, 1985).
The gradeline method should be employed, sometimes referred to as "zero-line method, which has proved to be the ideal tool for fitting the road to the natural terrain as closely as possible. It can be described as a step-by-step method for fixing the location line with a given longitudinal gradient directly in the terrain (Litzka & Haslehner, 1995) by means of a hand-held clinometer. The gradeline itself represents the intersection between subgrade of the road and the slope, and serves as the guideline for mechanized road construction (Sedlak, 1985).
In using this simple method there are no real limits to project accuracy (Litzka & Haslehner, 1995) as exact costing of earthworks is not necessary due to the high performance of the construction equipment employed. Such simple methods must not be confused with inadequate planning as skill and experience are required to find the most feasible road alignment, both from the environmental and economic point of view. (Sedlak, 1985).
Figure 3. Road template
Once the gradeline is staked, clearing of the construction area by felling the trees within the clearing limits (see figure 3) should be carried out. In difficult terrain the clearing limits are marked by tying coloured plastic tapes to trees or branches.
The felling itself has to take account of the anticipated method of extraction by the excavator operator with regard to felling direction and harvesting method to be used. A modified full-length method is normally applied as it facilitates log removal from the construction area by excavator most efficiently. This method requires that trees are delimbed and topped at the felling site, except where the trees are too large to be handled by the excavator, when some cross cutting will be necessary.
Photo. Full-length method should preferably be used in felling at construction site
The introduction of hydraulic excavators in forest road construction has been the major step towards environmentally sound road construction practices. In hilly terrain the use of excavators can not only replace bulldozers in forest road construction but also improve the quality of roads while reducing environmental impacts of these complex engineering structures, whereas in steep terrain their use is the only option to make road construction feasible.
Road construction technique by hydraulic excavator comprises the following five distinct phases stated below:
i) log removal from construction area
ii) topsoil removal from construction area
iii) excavating base for fill foundation
iv) fill slope construction
v) subgrade and cut shaping
This order is not necessarily be followed in the actual construction sequence on the construction site. Some operators will arrange single activities in sequence, whereas others will chop and change between tasks. The latter are at risk burying organic materials in the fill and failing to separate excavated local materials taking account of their anticipated use in building up the fill in layers.
However, even if a well-trained and experienced professional operator follows his personal optimum sequence of construction activities, log removal from the construction area will always be the first phase in road construction and close supervision has to ensure best construction practices to be followed and compliance with the project plan approved by the authorities. The road gradient should frequently be checked to ensure that the gradeline is followed since stakes marking the gradeline can be obliterated during topsoil removal.
Figure 4. Road construction technique by excavator
Close supervision is important when road construction works are carried out by contractors who are paid per running metre of road completed rather than on an hourly rate. Past experience has shown that contractors payed by the running metre tend to decrease their own costs by poor construction practices (see also chapter 5.1.1) where proper establishment of the fill foundation is often neglected. Road failures and even landslides triggered by construction flaws have been the consequence, in particular due to the inadequate fill foundation provided by the excavator in the third phase.
On slopes where substantial rock blasting is specified the topsoil removal from the construction area will be followed by rock drilling and blasting to facilitate a solid foundation.
i) Log removal from construction area
Once the trees have been felled within the clearing limits, road construction activities will start by log removal from the construction area. As already mentioned, trees should preferably remain in full length in order to minimize the delays to the work of the excavator and ensure maximum performance.
Photo 7. Log removal by means of chain attached to the bucket's hook
After several trees have been attached by means of chain to the excavator's bucket or sometimes just by balancing stems put on the bucket, the excavator pull or carry logs out of the construction area by moving backwards to road side storage. Logs should be stored at roadside in several places rather than transported over long distances to landings due to the low driving speed of excavators. Such frequent storage will reduce transport costs and facilitate any further processing.
Photo. Log removal at the construction site by means of the excavator's bucket
ii) Topsoil removal from construction area
The log removal phase will be followed by clearing the construction area from wood residues and organic topsoil. Bigger branches are piled up by pulling them with the bucket's shanks to be removed later and to be spread out on the fill slope. Deposition of branches on the fill slope helps to keep exposure of unprotected surfaces as short as possible, provides immediate erosion control from fill slope and facilitates an earlier natural or man-made revegetation.
Stumps, tree tops and other vegetative debris are removed by the excavator's bucket from the construction area in front of the excavator and placed by the operator with accuracy and care along the base of the fill slope in order to form a filter windrow. The additional width between the construction limit and forest edge ensures that space is available to deposit debris outside the construction area and prevent organic material being mixed into the base of the fill.
In contrast to stump removal by bulldozers, where it is recommended to leave stumps 0.8 to 1.2 m high to provide added leverage (FAO, 1989), there is no need to do so in using excavators as stumps are being dug out. This ensures the highest wood recovery rate and therefore contributes to the economic feasibility of a road project.
The established filter windrow will reduce damage to forest stands alongside the road by excavated materials, namely stones, escaping downhill and also prevents sediment from entering into stream channels.
After stump removal has taken place, the organic topsoil will be stripped and material unsuitable to be used in the fill will be removed from the construction area and placed in the verge between the construction limit and the forest edge above the already established filter windrow. If working in grassland or where grass covers the forest floor the operator should be advised to separate and to lift turves carefully as they can be used to establish vegetation on the fills rather quickly.
Photo Wood residues and organic top soil will removed in front of the machine and spread on the rear fill slope
iii) Excavating base for fill foundation
At the toe of the anticipated fill slope a base, about 1 m wide and 0.5-1.5 m high, is excavated to establish the foundation for the fill on solid ground. The steeper the slope the deeper under subgrade level the base will be established limited by the excavator's maximum digging depth. Excavated materials should be separated by the operator taking account of their anticipated use in building up the fill.
Earth will then be deposited parallel to the toe of the fill slope, immediately above the established filter windrow to provide the downhill raised borderline of the foundation base and forming the lower part of the fill widening (see figure 3). Excavated mineral soil suitable for use in fill construction is temporarily heaped uphill on the construction area next to the excavator. Big boulders suitable for retaining structures are piled separately, either alongside the road or next to planned culverts.
In steep terrain where slopes with rock formation near or above ground level are to be crossed, the base for the fill foundation should be provided by breaking out rock either by rock hammering or rock blasting.
Upon this solid base, boulders are placed by the excavator with accuracy and care, as well as compacted by means of the excavator's bucket in order to build up a solid foundation for the fill. The establishment of a fill foundation reduces the length of fill slopes considerably and makes road construction in steep terrain feasable. This feature is of great importance when side slopes exceed 40 percent as balanced road sections can be achieved with considerably less excavation (FAO, 1989).
In contrast, applying traditional side cast techniques by bulldozer the length of the fill slope would amount to about 3.5 m, 12 m and 22 m for slope gradients of 45 %, 60 % and 70 %, assuming an angle of repose for side cast material of about 37°, and on slopes of over 75 % a fill cannot be established at all (Gorton, 1985). It is suggested that a balanced road design provided by excavator construction results in approximately 25 to 35 percent less excavated material compared to the traditional side cast technique by bulldozer where most of the road width is cut into the stable hill side (FAO, 1989).
Photo 10. Excavating a solid base for the fill foundation
iv) Fill construction
The main feature of road construction technique by hydraulic excavator is balanced road sections where cut excavation is incorporated into the layered fill. Suitable coarse material is placed against the fill foundation to establish the base fill layer. In general, the fill needs to be built up in well compacted layers to develop strength since it must support traffic. The excavated materials are spread by the excavator's bucket to form a 30 to 50 cm layer which is to be compacted by several excavator passes before being covered by the next layer of less coarse material.
The obvious advantage of balanced road design where is that loose, unconsolidated wasted material is minimised compared to traditional road construction techniques by bulldozer. Creating the road foundation on fill material requires highly skilled and experienced operators, as poor quality work in building the foundation may destroy parts of the roads and trigger landslides in steep terrain making large areas unproductive and inflicting scars on the landscape.
Photo. Fill construction is one of the most responsible duty in proper road construction - one can see the separated materials piled hillside
Only mineral soil, free of organic debris such as stumps, tree tops and humus should be used in fill construction as organic material will decompose and result in uneven settlement and increase the potential for failure. Excess material will, depending on its size, either be incorporated in the road subgrade of already established road sections or temporarily laid aside for use in the next work cycle. If excess material cannot be used, excess material can be removed with a dump truck.
v) Subgrade and cut shaping
The last exercise to be accomplished using the hydraulic excavator will be finishing the subgrade, establishment of the hillside ditch and final shaping of the cut slope.
Smaller holes in the uppermost fill layer will be filled up while the layer gets continuously compacted through excavator passing in order to achieve a firm subgrade. Finally smoothing and compacting of the subgrade surface by means of the excavator's bucket will provide the coarse subgrade.
Photo Smoothing and compacting the coarse subgrade by means of the excavator's bucket
Depending on the parent material at the construction site and the availability of material suitable for gravelling, a sealing layer of gravel or similar material should be applied on the coarse subgrade, (Photo 13), compacted and finally shaped and smoothed in order to provide a crowned road (Photo 15) or sloped roads if specified by the supervising forest engineer. All of these activities can be carried out by the excavator.
While the final finishing work is being done to the road surface, the hillside ditch can be formed. This allows for immediate draining of the road structure preventing damage to road structure and erosion from exposed surfaces during the construction phase as favourable weather conditions for road construction work often rapidly deteriorate in mountainous regions of Austria and heavy thunderstorms force to close road construction work.
After the ditch is formed final shaping of the cut slope to provide the desired slope gradient. The edge at the top of the cut is to be rounded in order to avoid overhanging floor vegetation and the cut slope to be smoothed in by the excavator's bucket in order to prevent downhill drifting of loose cut slope material after completion of the road (Photo 14). Material eroded and escaped into the ditch not only increases maintenance costs as it has to be removed, but also obstructs water drainage
Photo. Suitable local material wilt be spread on the coarse subgrade by the excavator to provide a sealing layer
After the road construction work by excavator has been finished, the forest road is left in a condition that will allow hauling trucks and off-road vehicles to pass (Photo 15). Although immediate access is provided, hauling should be restricted to trees harvested during road construction in order to avoid deterioration in timber quality. Otherwise, roads which have usually been constructed during the summer season, should be allowed to go through an entire winter and the subsequent melt-season before permitting their use by heavy machinery.
During the following construction season the road will finally surfaced. Settlement will be corrected and gravel will be applied to the running surface. The final smoothing and shaping of the road surface will either be accomplished by means of a grader or occasionally by excavator equipped with a slope finishing bucket. Following up the grader is a vibration roller providing a smoothed, compacted surface to ensure an effective drainage from the road surface.
Where rock surfaces are to be crossed, final shaping of the cut slope and establishment of the ditch will be provided by means of hydraulic hammer attached to the excavator. In such road sections the longitudinal water drainage facility can best be described as a deepened road edge rather than as a real ditch. Work should be done so that road width and rock disintegration can be kept to the absolute minimum.
Photo. Final shaping of the cutslope by means of the excavator's bucket
Photo. A sealing layer of gravel or similar material will be applied on the coarse subgrade and finally shaped to provide a crowned road
10.3.1 Hydraulic hammers
10.3.2 Rock blasting
10.3.3 Mass transport
10.3.4 Road drainage
10.3.5 Surfacing and shaping
10.3.6 Slope protection and stabilisation
The steeper the slopes the more rock disintegration will be involved in road construction activities since rock outcrops cannot be bypassed or rock surfaces avoided. The excavator production rate approaches the bulldozer production rate as side slope increases due to the fact that the excavator's bucket is much more effective at ripping than the dozer blade (FAO, 1989). The excavator production rate may even be higher on slopes steeper than 60 % as indicated by performance studies carried out under similar terrain conditions (Gorton, 1985).
Photo. As long as rock can be ripped, the excavator solely equipped with a suitable type of bucket will be employed in rock disintegration
Whether or not a rock can be ripped, rock excavation can be accomplished by means of excavator solely equipped with the a suitable type of bucket or other excavator attachments like hydraulic hammers or hydraulic drilling units. Pneumatic equipment is now widely replaced by hydraulic equipment which is not only quieter than pneumatic hammers, but also operates at lower cost as the excavator's hydraulic pumps do the work and an air compressor is not needed.
However, as long as the rock can be ripped, the excavator equipped with a suitable type of bucket can be employed. Since ripability of rock depends on the type of rock and on the degree of fracturing and/or weathering, the experienced planning engineer will arrange equipment needed in rock disintegration to be available at times which minimise down time for the excavator.
Photo. The use of hydraulic hammer close the gap in rock disintegration by rock buckets on the one hand and by blasting on the other hand
The use of hydraulic hammers attached to excavators is considered the ideal solution for rock disintegration in order to avoid rock blasting where the parent rock is no longer rippable by the excavator's bucket but still has enough planes of weakness for economical operation with hydraulic hammer. Although tremendous progress has been made in drilling and blasting techniques in the past, rock disintegration by hydraulic hammer does reduce environmental impacts.
Since a hammer need not to be a full time attachment and coupler systems provided by manufacturers ensure that there is no loss of bucket breakout force by their use, the bucket can be taken off and replaced by a hammer within a few minutes. Hydraulic hammers therefore make an excavator even more versatile and cost effective as drilling equipment and explosives are not needed to break out pockets of rocks and alterations in road location can be avoided.
The main features of hydraulic hammers and advantages inherent to their use can be described as follows:
· rock hammers are enlarging the application range of excavators;· less non-work time of the excavator operator as interference of blasting operation does not occur;
· desired cut slope gradient and shaping can easily be performed by the skilled operator;
· size of disintegrated rock material can be controlled by a skilled and experienced operator in order to facilitate incorporation of rock material;
· accurate construction of hillside ditch for water drainage;
· less excess material to be removed through accurate rock disintegration;
· the hydraulic hammer is the only equipment needed in addition to the excavator already employed at construction site; blasting danger can be avoided
In difficult terrain the decision on road location is based on the principles of best road construction practice, limitations due to forest ownership, and on terrain constraints. Therefore rock surfaces cannot always be avoided and substantial rock blasting may be specified by the planning engineer.
Although more sophisticated blasting techniques have been developed, rock blasting is best avoided as the use of rock drilling equipment and explosives increases road construction costs and there are substantial risks in using explosives
However, if blasting is specified, sophisticated drilling equipment attached to the hydraulic excavator, which facilitate vertical as well as horizontal drilling, should be used. Since there is no real limit to the drilling position, the blasting technique can be adjusted to rock condition and the use of an excavator as carrier vehicle ensures that the road width can be kept to the absolute minimum as excavators do not require additional road width for manoeuvre.
Photo. Sophisticated hydraulic drilling units for excavators enable vertical as well as horizontal rock drilling
The blasting technique used where the road has to be cut into stratified layers of compact limestone, can be described as follows:
· use of several vertical drilling holes instead of one long horizontal drilling hole as used in dolomite rock for example;· vertical holes were placed in a rectangular pattern 1.5 m square;
· hole length ranged from 3 to 4 m depending on the distance between rock surface and planned subgrade;
· amount of explosives loaded per drilling hole varied according to the hole length and ranged from 1.5 to 1.75 kg;
· use of sophisticated primers which facilitate loads to be exploded with delay in millisecond range;
· loads separated by the holes connected so that the explosion is caused by the same ignition.
This blasting technique using minor loads separated in several drilling holes with less disruptive effect on the bedrock can be described as "soft" blasting. On the one hand, it only loosens the rock to be removed by excavating but avoids disturbing the stratified bedrock as well as other blast-related damage. On the other hand, due to its less destructive effect, the size of rock material can be controlled which is important for subsequent use of disintegrated rock material in the road structure.
Photo. Proper blasting technique provides material suitable in size to be incorporated into the road structure while avoiding damage to the forest stands alongside road
The use of primers with delays allows the direction of movement of rock material caused by the explosion to be controlled. In general, the primers will be set in the holes following the staked road course so that the explosives loaded in the front holes will go off first and blasted rock material will be directed by the subsequent exploding loads towards the already established road section.
In road sections where substantial rock blasting is needed, full bench construction of road with longitudinal transport of excess material is usually specified and rock blasting along the base of the fill will be required in order to establish the base for proper fill foundation.
Damage to adjacent stands at construction site by material escaping downhill during blasting operations can be reduced due to the "soft" character of this blasting technique. Its use is also highly recommended in the vicinity of springs as they might be affected by the disruptive effect on stratified bedrock of less sophisticated blasting. If buildings or infrastructure are at risk even by applying soft blasting techniques, hydraulic hammers are the only solution but their use has to be restricted to short road sections for cost reasons.
One main advantage of road construction by hydraulic excavator, among others, is that balanced road construction with excavated material incorporated into the road structure can still be carried out on steep slopes whereas in road construction by bulldozers full bench construction technique with end hauling of excess material would have to be applied.
However, where rock surfaces are to be crossed and the base for fill foundation cannot be provided by the excavator, full bench road construction is unavoidable. The longitudinal mass transport will then either be provided by means of the excavator or by dump trucks depending on the amount of excess material to be removed.
In contrast to the statement that operating distance for materials movement by excavator is limited to its swing distance (FAO, 1989), longitudinal mass transport with distances of up to 70 metres was found at the study sites. Long distances for mass movement by excavator cannot be recommended in general, but are acceptable in road projects with only few short road sections where mass movement is needed and therefore the costly use of a dump truck can be avoided.
Another advantage of longitudinal mass transport by excavator is that the moved material will be incorporated in the road structure of already established road sections rather than wasted. Consequently, there is no need to find stable disposal areas which have to be integrated into the landscape. Furthermore, the incorporated and compacted material is unavailable for erosion. The experienced supervising engineer will decide whether excavator or dump truck should be employed.
The most effective way to prevent watershed disturbance and increased soil erosion rates is to minimise the total length of roads. It has to be kept in mind that even the best developed drainage system established during the road construction process will only reduce rather than avoid impacts on natural watersheds.
Nevertheless, forest roads are essential for industrial timber extraction, for providing convenient access to the forest for applying sustainable forest management practices and for monitoring purposes while often benefiting local communities at the same time (see also chapter 2).
Some of the most common drainage-related problems are:
· inadequately sized stream crossings, in particular culverts;
· inadequate road surface drainage;
· poor drainage of skid trails joining roads;
· lack of road maintenance after logging operations, hauling activities or erosion caused by thunderstorms so that ditches and culverts do not work.
Following environmentally sound construction practices, the measures stated below are considered obligatory to provide satisfactory water drainage and consequently to prevent erosion:
· the road fitted as closely as possible to the terrain and to be restricted in width to the absolute minimum for safety and anticipated use;· soil disturbance and surfaces exposed to erosion are to be minimized by balance of cuts and fills;
· road gradients should be varied to reduce concentrated flow on road surfaces, in ditches, in culverts and on fill slopes;
· gravel should be applied on the running surface not only for more convenient use by vehicles but also to provide a more weather resistant sealing surface;
· surface water from joining skid trails should be prevented from flowing on to the road and becoming man-made streams with the potential for erosion as they flow downstream;
· ditch gradients should be adjusted to the specific soil condition at the construction site to keep collected waters moving to culverts and preventing sediment deposition and ditch erosion;
· road drainage features are to be designed and spaced so that peak drainage flow from surfaces will not exceed the capacity of the individual drainage facilities;
· culvert location are to be spaced not only at certain distances but are to be installed where actually needed when crossing streams either perennial or intermittent, and in ephemeral areas;
· prefabricated steel culverts pipes are to be installed in preference to articulated concrete pipes as the latter are at risk of collapse under the load of heavy hauling during periods of weakened road strength and consequently to obstruct or to block water drainage;
· culverts are to be protected from plugging by using sediment catch basins and debris racks where needed and water is to be prevented from eroding and undercutting the culvert by rock armoured inlets;
· outlets of culverts are to be armoured with rock boulders to prevent emerging water from eroding the fill slope where water will not be released onto a stable area;
· fords should be considered as alternative to culverts in crossing perennial streams carrying high loads of sediments or the combined use of culvert and ford, in particular where torrents are to be crossed, with a culvert for the normal run-off and a ford for high floods;
· individual drainage facilities are to be inspected periodically for need of maintenance and following after heavy thunderstorms and after logging and hauling activities in order to start immediately repair work if needed;
· forest debris to be cleared from ditches and culverts
· damage to road features should be avoided by effective road-use management which includes access control in general as well as road closure during wet seasons.
Photo. Water drainage is to be ensured from the start - intermittent springs often appear after heavy thunderstorms and transfer water from planes in the bedrock onto the newly established cut slope and might trigger slides
Photo. Slope material escaped into the ditch requires immediate action to avoid obstruction of water drainage and to prevent costly repair work of slips
One significant feature in road construction by excavator is the fact that drainage facilities and erosion control features will either be provided in each single work cycle of the ongoing road construction process or can easily be established by means of excavators at any time required without need for additional machinery. In general, culverts will be installed when the road cross section is established either for the entire road or for those parts finished during the construction season.
In general, minimum gradients of 2-3 % and maximum gradients of 9-12 %, in exceptional cases up to 16 % are considered appropriate for forest roads (Sedlak, 1996). Gradients for the road crown will range from 2 to 5 % and from 3 to 6 % for insloped roads (Winkler, 1992) to ensure an effective drainage from the road surface.
Ditch gradients should range from 2 to 8 % (Almas et al., 1993), just steep enough to keep collected waters moving without carrying excessive sediments. Gradients steeper than 8 percent might result in too much momentum of collected water and the carrying of sediment and debris for long distances, whereas gradients which are too shallow lead to silting up of ditches. Culverts should be maintained in order to avoid failure due to plugging by debris and sediment.
As one can see from the specifications made by the authorities (Table 6) for the individual road projects, fords are often specified in crossing perennial streams. This reflects the environmentalists' general preference of fords against culverts (Sedlak, 1996) as the latter are considered to interfere with the stream ecosystem.
Once the road subgrade has been constructed and culverts have been established, the road is allowed to go through an entire winter and the subsequent melt season, before surfacing takes place during the construction season in the following year. Settlement in the road subgrade are filled with coarse gravel and well-graded gravel is applied on the running surface. Only the use of well-graded material, where smaller particles tend to fill the empty spaces between the larger particles during compacting performed by rollers, will ensure that a smooth sealing surface can be achieved.
Once the gravel has been applied on the running surface the final shaping and smoothing will usually be provided by means of a grader. Depending on the material applied the final shaping will occasionally be done by an excavator equipped with a slope finishing bucket as at study site 3 where limestone material from local quarries was used for surfacing.
Finally, following up the grader is a vibration roller for proper compaction. Compaction is the process of increasing the density and the strength of the soil. The effectiveness of the compacting process will be affected by gradation of gravel material applied, its moisture content and the compactive effort. Proper compaction of fill material is not only the key to a stable, balanced road design (FAO, 1989) but also results in a significant reduction of maintenance cost and helps prevents erosion.
Photo. Shaping of the gravel material applied on the running surface will occasionally be carried out by an excavator solely equipped with a slope finishing bucket
The costs of using well graded material for the road pavement can be substantial (Almas et al., 1993) and could cost as much as 70% of the total cost of the road on weak clay subgrades (Sedlak, 1996). The use of substitute poorly graded material is not recommended. The initial financial savings are soon overtaken by the higher maintenance costs.
Options for saving on the costs of gravel material are given below (Sedlak, 1996)
· road construction during frost periods to prevent subgrade deformation and the need to fill up settlements with costly gravel;· recycling or processing local material wherever feasible;
· use of polypropylene fabric layers between subgrade and gravel layers to prevent clay intrusions;
· subgrade stabilization using lime or other suitable substances as recommended in the road engineering literature.
At the study sites the costs of surfacing which cover the cost for gravel material itself and its transport, for grader as well as roller operations, ranged from about 4 to 47 percent of the overall road costs (see chapter 5.3) at the three construction sites and are less than the costs mentioned above due to the availability of suitable gravel material from local quarries.
Photo. Topsoil removal will be spread on the rear fill slope in each work cycle
Some of the measures which are usually undertaken to stabilise slopes and to prevent erosion from exposed surfaces, will already be performed in each single work cycle as they are inherent features of proper road construction technique by excavator. In particular these measures are the following:
· a fill slope cover which provides immediate erosion control will be continuously performed during the phase of topsoil removal from the construction area in each single work cycle of the road construction process;· finally shaped, smoothed and compacted cuts performed in each single work cycle ensure that loose material is removed from slope surfaces which would otherwise be exposed to erosion;
· inlet and outlet protection structures of culverts as well as retaining walls for slope stabilization will be built up by the excavator using the boulders which have been separated from other excavated materials during construction operations;
· the fill slope will be revegetated by turfs where a grass layer covered the soil at construction site.
Beside the measures already performed by applying the excavator construction technique, vegetative treatment of slopes for early revegetation and prevention of erosion has become a standard procedure in Austria (Sedlak, 1996. There is a wide spectrum of bioengineering measures which range from simple seeding procedures, mulching etc. to combined use of retaining structures and living plants. Employing bioengineering methods not only prevent erosion but also ensure a better blending into the landscape and sometimes perform an additional benefit due to the draining effect of structures incorporating living plants. These bioengineering methods are generally preferable to purely technology-oriented methods such as concrete supporting walls (Litzka & Haslehner, 1995).
Photo. Erosion control of fill slope by debris cover provided immediately after fill construction
Photo. Immediate erosion control of cut slope by stumps which had been removed during the phase of topsoil removal from the construction area
Photo. Retaining walls built up from boulders by means of excavator are quite costly but cannot always be avoided in crossing wet and unstable areas due to terrain constraints in road location in mountainous regions
Regardless of the type of construction equipment used in a particular project, road construction itself remains a difficult, often hazardous operation in mountainous terrain that can inflict scars on the landscape as well as substantial damage on the forest ecosystem. In order to carry out construction operations efficiently and safely, as well as in an environmentally sound way the following I should be considered:
· appropriate size and power configuration of construction equipment, adjusted to the actual needs of the construction technique applied and with respect to terrain conditions;· appropriate equipment with respect to technical and safety standards, as well as ergonomic principles and requirements;
· only adequate trained, skilled and experienced machine operators should be employed for road construction in sensitive forest ecosystems and difficult terrain;
· well planned road design followed by fitting the road to the natural terrain as closely as possible to facilitate road construction without major problems for operators and machines;
· clear instruction to and close supervision of machine operators by the forest engineer responsible for road planning and construction.
The appropriate type of hammer can be selected out of a hammer series with operating weights ranging from 150 to 3500 kg for all types of carrier units ranging from 1.5 to 80 tonnes (Wimmer, 1996). The type of hydraulic hammers used are distinguished by a newly designed impact technique which guarantees high impact energy with low back thrust.
The design of the c hammer enables it to be exactly positioned by the operator as the housing does not have any protruding parts (see Photo 17). This new generation of hydraulic hammers provides a better working environment for the operator because of the sound proofing and vibration damper systems, the latter also reduces the impact to the excavator's boom.
The hydraulic drilling unit AB3000T used enables vertical as well as horizontal drilling by the operator as the drilling unit has 360° unlimited rotation and a swivel axis turnable by 95° (Wimmer, 1996). A no load stroke as well as an automatic antibloc system facilitates drilling in geological difficult terrain. Furthermore, the drilling unit is equipped with a radio remote control system to ensure the operator always has the optimal view to control the drilling unit. The drilling unit has its own generator so that no additional electrical installations at the excavator are necessary.
It should be noted that although road construction is machine-intensive, labour remains the most critical element for achieving the goals of environmentally sound road construction practices. Only if workers are competent in their skills, and motivated to work properly and efficiently can they be expected to contribute effectively to these goals (Dykstra & Heinrich, 1996).
Since productivity is defined as the rate of product output per time unit for a given production system, the production rates of a studied system can easily be estimated if time studies combined with measurements of the output of production have been completed.
The estimated production rates for excavator operations are based either on the total workplace time or total work time used to perform a certain length of road by the excavator operator at all study sites, regardless of whether a hydraulic hammer has been used or not.
All other construction activities where an excavator will be employed (culvert, retaining structures), might be employed (shaping after surfacing) or might serve as carrier unit (rock drilling) are not included in the estimates of production rates, neither for workplace time-based nor for work time-based estimates.
Table 13. Estimated production rates in road construction by excavator
|
Study site |
side slope |
Production rate |
Production rate |
subgrade width |
|
Study site |
[%] |
[m/h WP] |
[m/h WT] |
[m] |
|
Study site 1 |
50-55 |
5.69 |
6.26 |
4.5 |
|
Study site 2 |
40-45 |
5.24 |
5.77 |
6.5 |
|
Study site 3 |
75-80 |
2.42 |
3.05 |
4.2 |
Note: WP... workplace time
WT... work time
Based on the hourly productivity found in the studies and on an assumed workplace time of 8 hours per day, the productivity rates range from 16 metres to 48 metres of road per day, where the first figure can be considered indicative for extreme difficult terrain and the latter for favourable conditions in mountainous terrain. It is noteworthy that the actual workplace time observed during the studies often exceeded the regular workplace time for employees of 8 hours per day as the operators tended to make use of favourable weather conditions for construction work.
The estimated performance rate for blasting operations is based on the workplace time used for rock disintegration of a certain volume of rock by means of explosives. Since the vertical drilling holes were placed in a rectangular pattern 1.5 m square in each single blasting operation at the study site, the volume of disintegrated rock has been estimated separately for each blasting operation by multiplying the squared distance between holes by the length of holes and the number of holes.
Time calculations to estimate performance rates of blasting operations based on the total workplace time are considered to be not indicative as the non-work time of the blasting operator can dramatically be decreased by flexible and proper timing of construction and blasting operations as done at the study site.
Therefore, the performance rate stated below is based on the work time only. The efficiency level found at the study site, as the rate of time input per a certain volume of rock to be disintegrated, was about 2.13 min/m3 reflecting an average volume of load of about 76 m3 per blasting operation. The performance rate based on all blasting operations observed amounts to 28.18 m3/h of work time.
The estimation of production costs is based on the production and performance rates stated in previous chapters for construction and blasting operations and the hourly costs for construction workforce and equipment involved in both road construction and blasting operations. The hourly costs for workforce and equipment are based upon information obtained from the supervising forest engineer of the Federal Forest Service of Salzburg.
Refinement work stated in table 14 refers to final shaping and compaction work of the fill slope at study site 1 for part of the road section under review. At study site 3 it refers to incorporating excess material into the road structure after transport by a dump truck. In this particular case incorporation work was carried out by means of a small excavator hired for a few days of anticipated need and which was operated by the blasting operator.
The use of the small excavator provided an effective means of arranging the work in a way that dramatically reduced the non-work time of the blasting operator. It should be noted that in hiring additional equipment, proper timing becomes very important in order to achieve the desired objective of overall cost reduction in road construction.
Table 14 shows typical examples of costs for equipment and standby workforce as well as costs for each activity carried out and observed by the work and time studies at the study sites in road construction. As conditions for construction work may considerably vary along the road course, the construction costs stated in table 14 refer to the particular road section under review of each road project only. For details compare corresponding figures on cost of construction work by excavator stated in table 14 and table 15.
Table 14. Estimated costs of road construction work by excavator
|
Production costs factor |
unit |
Study site 1 |
Study site 2 |
Study site 3 |
||||
|
cost/unit |
cost |
cost/unit |
cost |
cost/unit |
cost |
|||
|
[US$] |
[US$/m] |
[US$] |
[US$/m] |
[US$] |
[US$/m] |
|||
|
construction work |
|
|
|
|
|
|
|
|
|
|
hydraulic excavator |
[h] |
56.67 |
9.96 |
91.67 |
17.49 |
57.50 |
23.76 |
|
|
hydraulic hammer |
[h] |
- |
- |
39.17 |
0.15 |
39.17 |
1.80 |
|
refinement work |
|
|
|
|
|
|
|
|
|
|
hydraulic excavator |
[h] |
56.67 |
0.16 |
- |
- |
45.00 |
3.51 |
|
rock blasting |
|
|
|
|
|
|
|
|
|
|
hydraulic drilling unit |
[h] |
- |
- |
- |
- |
95.83 |
24.33 |
|
|
explosives primer |
[kg] piece |
- |
- |
- |
- |
5.42 2.50 |
10.51 3.14 |
|
|
operator (standby) |
[h] |
- |
- |
- |
- |
37.50 |
5.48 |
|
mass transport |
|
|
|
|
|
|
|
|
|
|
dump truck |
[h] |
- |
- |
- |
- |
48.33 |
5.66 |
|
total construction cost |
|
|
10.12 |
|
17.64 |
|
95.83 |
|
The cost estimates stated in Table 14 refer to the road in the stage of finished subgrade and subsequent establishment of hillside ditch as described in chapter 3.2 and do not include any further construction activity which will be or might be performed by excavator at a later stage such as to install culverts, to build up retaining structures or to final shape the road after surfacing.
Table 15. Estimated overall construction costs of road projects
|
Production costs factor |
unit |
Study site 1 |
Study site 2 |
Study site 3 |
||||
|
cost/unit |
cost |
cost/unit |
cost |
cost/unit |
cost |
|||
|
excavator operations* |
|
n.a. |
11.97 |
n.a. |
17.52 |
n.a. |
70.27 |
|
|
culvert (incl. in-/outlet protection) |
piece |
32.92 |
0.66 |
32.92 |
0.66 |
32.92 |
0.66 |
|
|
culvert pipe |
|
|
|
|
|
|
|
|
|
|
hydraulic excavator |
[h] |
56.67 |
1.13 |
91.67 |
1.83 |
57.50 |
0.86 |
|
surfacing material |
[rm] |
1.04 |
1.73 |
1.04 |
1.04 |
1.67 |
0.25 |
|
|
|
gravel transport |
[rm] |
5.83 |
9.72 |
5.83 |
5.83 |
5.83 |
0.88 |
|
grading/shaping motor grader |
[h] |
77.08 |
0.44 |
77.08 |
0.44 |
- |
- |
|
|
|
hydraulic excavator |
[h] |
- |
- |
- |
- |
57.50 |
1.05 |
|
rolling |
[h] |
59.58 |
0.96 |
59.58 |
0.48 |
59.58 |
0.48 |
|
|
seeding |
[m2] |
0.15 |
1.01 |
0.15 |
1.13 |
0.15 |
1.17 |
|
|
overall road cost |
|
|
27.62 |
|
28.93 |
|
75.62 |
|
*) corresponding with the total construction cost estimate n.a. not table 14 applicable
The estimated overall construction costs of the three road projects under review stated in table 15 are based on the actual costs spent on excavator operations including rock disintegration during the construction season of 1997 in the road projects under review and the assumed costs of construction activities required to finalize the road.
The cost assumptions made for installing culverts including retaining structures, for surfacing, grading and rolling of the road as well as for seeding of slope surfaces are based on the personal experience of the supervising forest engineer. Since these activities had not been observed by work and time studies estimated costs have been used.
In mountainous terrain where forest stands not only sustain site productivity by preventing soil developed over centuries to be eroded but often protect human settlements, infrastructure and other land uses from torrents and avalanches, avoidance of site disturbance is imperative. On the other hand, active management of overmature stands on steep slopes which are at risk of loosing their protective function, requires a minimum of forest access provided by forest roads.
Enhancing forest road construction practices, the use of hydraulic excavators and employment of advanced drilling and blasting technology have been proven to be the best solution both environmentally sound and economically feasible, for road construction in difficult terrain.
In general, the features and advantages of the hydraulic excavator itself and it's use in road construction can be described as follows:
· the excavator basically operates by digging, swinging and either dumping or controlled placement of excavation depending on the task to be provided;· all tasks to be accomplished in road construction by excavator can be provided by operating from a fixed position or movement parallel to the road centreline so that no additional road width for manoeuvring is required;
· different types of buckets available and several attachments easily to be changed by quick coupling systems even increase the excavators' versatility to do a wider variety of work e.g. ripping, trenching, loading, compacting, hydraulic hammering or rock drilling;
· less need for blasting due to high ripping and breakout force of the excavator and, alternatively, the use of hydraulic hammer for rock disintegration.
The features and advantages of advanced drilling and blasting technique are:
· the type of hydraulic drilling units used, attached to the excavator, facilitates vertical as well as horizontal drilling and therefore to optimise and adjust blasting technique with regard to rock condition;· "soft" blasting with less (fracturing) disruptive effect on the bedrock avoids loosening of stratified rock (and/or fractured) as well as other blast-related damage;
· "soft" blasting techniques with less destructive effect enable to control the size of rock material provided;
· "soft" blasting techniques only loosen the rock for being excavated rather than brealing out;
In making use of the advantages of construction equipment and techniques mentioned above, the skilled and experienced operator is provided with an effective tool to minimize environmental impacts of road construction activities. This environmentally sound practice of road construction is characterized by:
1) reduced area dedicated to forest roads as:
· additional road width for manoeuvre of construction machinery is not needed; the subgrade width is kept to the absolute minimum determined by safety and anticipated use;· the length of fill slope can be reduced due to a solid fill foundation established by means of the excavator and the overall construction width is reduced;
2) reduced disturbance of the landscape as:
· clearing width is reduced as a result of minimized overall construction width and disturbance of canopy and related impacts are reduced;· cut heights are reduced because of minimized overall construction width;
· roads are designed to balance cuts and fills wherever possible, less rock disintegration is needed and less material is to be excavated;
· the use of hydraulic hammers facilitates accurate rock excavation; over excavation of rock can be avoided;
· rock disintegration by hydraulic hammer and "soft" blasting provides material suitable in size to be incorporated in the road structure, the need for borrow pits (quarries alongside road) is reduced;
· measures are undertaken to stabilize and revegetate cut and fill slopes immediately after completion of road construction work, scars inflicted on the landscape are quickly remedied;
3) satisfactory water drainage and effective erosion control as:
· drainage facilities can already be installed by the excavator during the ongoing road construction process at any time if required;· most of the excavated material is incorporated in the road structure and properly compacted, it is very likely unavailable for erosion;
· cut and fill slopes are final shaped and compacted by means of the excavator's bucket to prevent erosion;
· branches removed from the construction area are spread on the fill slopes the exposure to erosion of unprotected soil is minimized;
· retaining walls for slope stabilization can be established during road construction at any time if required;
4) negligible damages to stands alongside road by rock materials escaping downhill as:
· the excavation is incorporated into the road structure instead of being side cast and excess material from full bench road sections is end-hauled to stable disposal areas;· the placement of excavated materials can excellently be controlled by the skilled excavator operator and loose material which might escape during construction activities will be trapped by a slash filter windrow established at the base of the fill;
· the use of rock buckets and hydraulic hammers widely replaces the need for blasting where hurled stones or escaping rocks might cause some damage even if advanced blasting techniques are applied;
· "soft" blasting techniques with less destructive and bursting effect are employed if substantial rock blasting is specified;
