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7.5 1600 1400 1200 1000 DM/m 800 600 400 200 0 Berlin 1997 0 10,00 11,00 12,00 13,00 14,00 16,00 18,00 Open construction Micro-tunnelling Comparison of costs for constructing house connections above the water table (open construction / micro-tunnelling using vitrified-clay pipes) Unpaved Interlocking setts Bitumen paving Comparison of costs, house connections There is nothing in the foregoing remarks about the costs of house connections. These are covered in a further example (Fig. 32) which likewise compares the costs of open and trenchless construction. In each case costs have been calculated for house connections between 10.00 and 18.00 metres in length where the surface is unpaved and for road surfaces of interlocking paving bedded in gravel and bitumen paving. The surface between roadway edge and plot perimeter is – except in the case of the fully paved surface – constant for all other examples at a total width of 4.50 metres, comprising – 1.00-metre-wide unpaved tree-protection strip, – 1.00-metre-wide cycle track of interlocking paving bedded in gravel, – 2.00-metres-wide footpath of concrete paving blocks bedded in gravel, – 0.50-metre-wide mosaic paving bedded in sand. The distance b from the collector under the roadway varies between 5.50 and 13.50 metres, yielding house-connection lengths between 10.00 and 18.00. Micro-tunnelling Page 29 HC length in m 1/2 roadway 4,50 In both construction methods one trench over the collector and one on the plot were allowed for. Pipe jacking for connecting sewers where only one trench is needed, e.g. in the Berlin method, jacking with underground connection to the collector, blind-hole boring naturally result in even distinctly lower construction costs and shift the cost-effectiveness threshold clearly in favour of trenchless laying. But even with two trenches and a completely unpaved surface the cost-effectiveness of the jacking method is already reached at a length of about 18 metres. With a roadway of interlocking paving jacking is more economic even at a house-connection length under about 10.50 metres and in the case of bitumen paving at a length of less than 10.00 metres. The remarks in the final paragraph of 7. apply analogously to construction of house connections. b b = 5,50 m = 6,50 m = 7,50 m = 8,50 m = 9,50 m = 11,50 m = 13,50 m Fig. 32
Page 30 Micro-tunnelling 7.6 Social costs Only construction costs actually incurred are considered in the foregoing remarks. Compared with open sewerconstruction methods the precisely calculable savings brought by micro-tunnelling result primarily from – the reduction in holes in the roads, – the absence of soil excavation involving transport of large bulks of soil, – the reduction in prior pipe diversions, – limitation of dewatering, for the last two of which no figures are included in the examples. In everyday construction activities, however, further advantages accrue for micro-tunnelling, such as – limitation of traffic disruption, – reduction in noise- and emission-levels, – reduced accident hazard, – elimination of damage to adjacent structures, – sparing of trees and parkland and by – elimination of time loss due to weather. These are referred to as indirect or social costs; they have particular significance for the environment and are primarily a charge on the national economy. Impediments to traffic flow, diversions, increased accident rates, road damage on the diversion routes, disruption of business, environmental nuisances such as noise, dirt and smell are their main components. The expense caused thereby in the case of open construction can be considerable and in conjunction with additional soil exchange, interim storage etc. can often reach the same order of magnitude as the direct costs for a construction project. While these social costs are not taken into account in awarding contracts for sewer construction, competition is distorted. That micro-tunnelling is nevertheless more and more becoming an economic alternative is evidence of its attractiveness. 8. Micro-tunnelling as an opportunity for lower sewerage charges Sewerage charges are determined essentially by the finance and ongoing maintenance charges for the plant and equipment for draining, moving and treating sewage, with the associated installations. According to Pecher, based on calculations by ATV, capital expenditure on sewage systems amounts to some 75% and thus has particular weight. (”Sewage disposal: costeffective, far-sighted, affordable”, Cost-effective Sewage Disposal Initiative (IWA), PO Box 101122, 45411 Mühlheim an der Ruhr). Sewerage charges derive from operating costs, the sewerage levy and imputed depreciation allowances and interest charges. According to the above source the cost shares yielded for public operators in all Federal States are: – sewerage levy 3.3 % – personnel costs 16.4 % – other operating costs 25.9 % – interest 29.1 % – depreciation 25.3 % Outlay on interest and depreciation thus makes up almost 55% of the charge. It follows that charges can be lowered by lengthening the service life of sewers. The service life of sewage systems can be affected by conscientious planning including careful selection of the materials to be used, quality-controlled construction work and proper operation. Reference is made in this connection to the aforementioned article by Pecher and to a publication by Kuck (”Paving the way for future generations: a plea for technical and economic farsightedness in the construction and operation of public sewage systems”, offprint from Local-government economics, Vol. 4, April 1997, obtainable from STEINZEUG GmbH, Cologne). Because of its particular technical requirements microtunnelling provides the best basis for creating longlasting sewers through high-quality construction. The requirements made under ATV A 125 of jacking pipes and their joint assemblies result in, amongst other things, greater wall thickness, greater strength and lower tolerances than in conventional pipes. The laying process ensures greater precision and less effect on insitu soil and the embedding. These specific features of micro-tunnelling give increased security against stress from shear loads, abrasion, corrosion, jetting etc. and extend the sewers’ service life. A longer useful life permits the depreciation period to be adjusted commensu-
Page 1 and 2: Cost-effective and environmentally
Page 4: Contents 1. Introduction . . . . .
Page 7 and 8: m 350.000 300.000 250.000 200.000 1
Page 9 and 10: Page 8 Micro-tunnelling Quite diffe
Page 11 and 12: Fig. 7: Non-controllable horizontal
Page 13 and 14: Page 12 Micro-tunnelling Elements i
Page 15 and 16: Page 14 Micro-tunnelling pipe. Used
Page 17 and 18: Page 16 Micro-tunnelling The follow
Page 19 and 20: Fig. 20: Berlin method: by-shaft be
Page 21 and 22: [m] 8.000 7.000 6.000 5.000 4.000 3
Page 23 and 24: Page 22 Micro-tunnelling - 6 classe
Page 25 and 26: Page 24 Micro-tunnelling 7. Cost-ef
Page 27 and 28: Page 26 Micro-tunnelling 7.2 6000 5
Page 29: Page 28 Micro-tunnelling 7.4 7000 6
Page 33: Page 32 Micro-tunnelling 6. For eve

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