Publications

Environmentally sound forest road construction in mountainous terrain

01.09.1999

The study was carried out in semi-natural forests of the Alps in the province of Salzburg, Austria. Although the concept of opening up forests by a permanent road network as a precondition for forest management and utilization of forests in a sustainable manner is widely accepted both to specialists and to the public at large, it is a difficult concept to put into effect particularly in sensitive forest ecosystems.

The road projects were selected to demonstrate that "Environmentally Friendly Forest Engineering" considerably reduces the effect of damaging elements of forest road construction. The study documents each phase of environmentally sound road construction by excavator and advanced blasting technique as applied in the road projects under review and compares its environmental impacts with those of the traditional road construction by bulldozers.

Data on road construction was collected under different terrain and formation conditions. Work and time studies on construction operations by excavator were carried out at all construction sites and blasting operations where observed in one road project where substantial rock blasting was specified.

The productive work time required per running metre of road constructed by excavator ranged from 8.75 min and 9.75 min at study sites 1 and 2 to 16.93 min at study site 3. These figures on productivity can be considered indicative for favourable, medium and extreme difficult construction conditions in mountainous terrain of the Alps.

The productivity per hour of workplace time varies even more due to the need for rock breaking by hydraulic hammer at study site 2 and the interference of blasting operations at study site 3. A productivity of 5.69 m/h workplace time was found under favourable conditions of study site 1 and of 5.24 m/h workplace time under medium conditions of study site 2. In the extreme difficult terrain of study site 3 the productivity dropped to 2.42 m/h workplace time.

All figures stated above on efficiency and performance rates of excavators under different conditions refer to the establishment of the cross section including the hillside ditch but do not cover any further activities usually carried out by excavators such as installation culverts or construction of retaining structures.

The productive work time required per blasting operation with an average rock volume of 76 m³ to be shattered was 115.22 min per blasting operation. The performance rate of rock blasting was 28.18 m³/h work time at the study site.

The cost per running metre of road constructed by excavator is based on the performance rates established by the work and time studies at each construction site and amounts to US$10.12/m for study site 1, US$17.64/m for study site 2 and US$95.83/m for study site 3. The stated figures on cost per running metre refer only to the particular road sections under review. At study site 3 where conditions for road construction varied between adjacent road sections of the project, the average cost per running metre of road dropped to about US$70.00/m considering the entire road project.

The overall cost per running metre of road completed is estimated to amount to US$27.62/m, US$28.93/m and US$75.62/m for the road sections under review. The overall cost per running metre differs less in degree between the study sites since the required activities for finishing the road vary considerably between the three observed construction sites.

The marked superiority of road construction by excavator, including the use of advanced blasting technique, over the traditional road construction techniques by bulldozers is underscored by the results of the qualitative assessment of environmental impacts in the environmentally sound road construction practice under review. This practice encourages a reduced area dedicated to permanent forest infrastructure, reduced disturbance of the landscape, satisfactory water drainage and effective erosion control as well as negligible damage to forest stands alongside road.

The implementation of environmentally sound road construction technique, characterized by use of excavator and advanced blasting technique as applied in the road projects is believed to provide a satisfactory solution to the unquestionable impact of timber harvesting operations on the environment. This technique developed initially for the Alpine mountain range of Austria is deemed to be the most suitable option for areas where sensitive forest ecosystems are to be opened up.

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