There are three variables of sustainability in relation to the most commonly used techniques (HDD, microtunnelling and minitrench).
From the strictly technological point of view, related to the working phases, the economic benefits of introducing no-dig techniques derive mainly from the reduction and certainty of the execution times of the work; the extreme reduction of the excavations and the working areas. Moreover it can be taken into consideration the reducing of cost of public and private transport, which route passes near the working areas. Obviously this last advantage is valid especially in the urban areas.
All the savings that compensate for the amortization of initial investments made by the company (complex machineries and workers’ specialization) and expenditure resulting from the need for accurate preliminary surveys (georadar/geoelectric/soil investigations). In particular, the reduction of the excavations is the most important parameter: in case of HDD, the open pit are strongly limited to the inlet and outlet of the pipes where the RIGS are located.
In case of minitrench the very small dimensions of the excavation involve a significant saving, compared to the traditional excavation. In addition, the least cost of public and private transport by the site, resulting from fuel economy and travel time, was estimated at -74% as compared to the traditional yard.
From the environmental point of view, the benefits are even more pronounced, and are all due to the elimination, or extreme reduction, of the open trenches:
- very small amount of waste material to be disposed of and new material for restoration (HDD and microtunnelling machine input and output, estimates of -90% for minitrench compared to traditional digging);
- less emissions of harmful substances during production for the use of materials (bitumen, binder, etc.) and especially energy needed during the production phase, especially for the use of machines (fuel and associated emissions, estimated -86% for HDD / Microtunnelling and -75% for minitrench);
- very few emissions resulting from the reduction of the traveling time of the surrounding vehicular traffic (estimate -75% for HDD / microtunneling and -74% for minitrench).
An overall estimate of the environmental impacts associated with HDD / microtunnelling and minitrench techniques leads to reductions of 84% and 82%, respectively. To these aspects are to be added those related to the energy efficiency represented by the no-dig technologies in the following table is expressed in TEP (Tonnes of Equivalent Petroleum) consumption by comparing the traditional excavation, HDD, minitrench in the realization of A one kilometre long plant. These values then translate into Energy Efficiency Titles (TEEs or White Certificates), which can be traded in the energy sector.
As above mentioned the percentage of savings have been tested for no-dig works in the urban areas for lay cables at low depth.
The social costs of open trenches are significant: from those due to the presence for a long time of large open trenches, to those regarding the risks of accidents for workers (and again, indirectly, for the community)
Accidents that may occur in this type of work, up to the costs associated with the likely recourse to poorly qualified worker, often associated with low-tech jobs and high work intensity. Conversely, the use of no-dig techniques involves almost total elimination of all these social costs:
- for the drastic reduction of the excavations and the open construction site, which eliminates the source of collective discomfort;
- to reduce the risk of accidents / accidents that may occur at the work site, where the only residual risk remains due to the correct use of the machines, which can be minimized by specific vocational training of the operators;
- for the elimination of the scarcity of skilled workers, since these jobs are “highly technological and highly specialized”.
To the wholly positive balance that we can draw from the comparison of the impact of no-dig techniques with traditional excavations, we must add a more general consideration regarding the positive effect on the economic system and the construction system.