The results of this case study show that environmentally sound road construction, as applied in the three road projects under review, is superior to road construction in the traditional way by bulldozers on steep slopes. The short-term economic benefits from use of bulldozers in forest road construction in mountainous terrain are likely in the longer run to create environmental damage on a considerable scale as side slopes increase.
Focusing on environmental impacts of road construction practices, the advantages of the environmentally sound construction technique by means of hydraulic excavator and advanced drilling and blasting techniques are obvious:
environmentally sound road construction by excavator |
traditional road construction by bulldozer | |
subgrade width can be kept to the absolute minimum determined by safety and anticipated use as the excavator operates from a fixed position or by movement parallel to the road centreline |
bulldozers can hardly be used at construction sites where minimum subgrade width is requested due to their need to manoeuvre | |
a balanced road design where suitable excavated material is incorporated in the road structure result in significantly less excavation when compared to full bench construction of road; in road construction by excavator the bench construction will only be applied on slopes where rock faces are to be crossed |
full bench construction will be applied as the side slope increases where the entire subgrade is cut into the hill and material will be side cast or wasted rather than incorporated | |
excellent control in the placement of excavated material as the excavator basically operates by digging, swinging and depositing material with accuracy and care |
inadequate control in placement of material as the bulldozer operates by pushing or drifting material in front of the blade to areas where fill is needed and/or side casting excess material | |
excavated material can be separated and temporarily piled by the excavator taking account of its anticipated use in building up the fill |
material from cuts cannot be separated to build up the fill in layers of suitably sized material | |
length of fill slope can be reduced due to the fill foundation established by the excavator; a solid fill foundation facilitates building a road in steep terrain |
length of fill slope will increase exponentially in steep terrain; on slopes over 75 % a fill cannot be established at all due to the angle of repose of side cast material | |
environmentally sound road construction by excavator |
traditional road construction by bulldozer | |
construction width is minimized as subgrade width and length of fill slope is reduced |
area dedicated to forest roads and disturbance of the landscape are higher when compared to road construction by excavator | |
as excavated material is incorporated in the road it is exposed less to erosion |
full bench construction provides a uniform subgrade but also a high potential for erosion by loose, unconsolidated side cast material | |
different types of buckets available enable the excavator to carry out specific construction work and ensure highest performance; the use of a rock bucket substitutes for other equipment as long as the rock can be ripped |
adequate road construction performed solely by bulldozer is considered to be restricted to construction sites where the road can be full benched and excavated material can be side cast and wasted | |
the use of hydraulic hammer which can easily be attached to the excavator result in less need for blasting and, consequently, in avoidance of blast-related damage |
if rock outcrops cannot be bypassed, rock blasting will be specified | |
as excavators enable the operator to efficiently dig, swing and place material with accuracy and care, damage to stands alongside road can result to be negligible |
material escaping during construction operation or excess material wasted downhill might cause considerable damage to forest stand alongside road | |
satisfactory water drainage and erosion control can be ensured from the start of work as culverts can be installed and retaining walls built up at any time |
culverts and retaining structures will be established after completion of bulldozer work | |
Apart from the above mentioned environmental advantages, economic components are important aspects of consideration in the environmentally sound road construction practice as side slope increases and rock disintegration is involved. As indicated in the literature by FAO (1989) and Gorton (1985), the economic advantage of road construction by bulldozer is most likely to disappear on slopes of about 50-60 percent and above.
Examination of the economic short-term advantage of bulldozer construction and the potential for medium and long-term damage and impact on the environment as well as on the landscape inherent in traditional construction techniques by bulldozer, should encourage the use of excavators in road construction even in less steep terrain.
The implementation of environmentally sound road construction technique is deemed highly necessary as forest roads are unquestionably the most problematic features of timber harvesting operations from the environmental point of view. The environmentally sound construction practice characterized by use of excavator and advanced blasting technique as applied in the road projects is considered a solution for mountainous terrain in general where areas of sensitive forest ecosystems are to be opened up, although it has been developed in particular for road construction in steep terrain in the Alpine mountain range of Austria.
