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Public bodies have a substantial demand for new underground utility pipelines in urban areas or for the rehabilitation or replacement of existing pipelines. The conventional method for meeting this need is by open trench construction. In urban areas, such trenching can result in significant vehicle traffic disruption, risk of personal injury or death, economic impacts on businesses, construction contractor claims, and unexpected administrative costs.
The availability of alternative pipeline replacement and construction techniques which can be accomplished without, or with only limited, trenching has substantially increased during the past few years. These techniques include:
* new installation
--micro-tunneling
--jacking and boring
--directional drilling
--fluid jet cutting
* rehabilitation of existing lines
--inversion thermal setting lining
--folded pipe insertion
--pushed-in short pipe lining
--pulled-in long pipe lining
--spray-on lining
--internal pressure grouting
* expansion of existing lines
--pipe bursting
These alternatives, often referred to as trenchless technology, are receiving increased attention and application for the construction, replacement, or rehabilitation of buried pipelines in urban areas since the First International Trenchless instruction of Utilities Conference in London in 1985.
In some cases the estimated construction cost of an appropriate trenchless alternative is less than the estimated construction cost of conventional trench-type construction. In these cases the selection of the trenchless alternative is generally appropriate if there are not other considerations such as anticipated useful life. However, it is the authors' experience that the estimated construction cost of trenchless alternatives is often higher than conventional trench-type construction. In these cases, public administrators and officials must have a rational basis for comparing alternatives and, if appropriate, justifying a recommendation to implement an alternative with a higher construction cost.
The purpose of this paper is to present a suggested procedure for comparing total project dollar costs and benefits to assist public decision makers in the selection of urban pipeline installation or rehabilitation alternatives. His procedure: (1) assigns dollar costs to the net effect of the project on society, (2) ignores economic shifts between individuals, and (3) accepts as already justified the basic decision to undertake the project.
PROJECT COSTS AND BENEFITS
The decision between conventional and trenchless construction for the construction or replacement of an urban pipeline should be made by a comparison of total project costs and benefits....