mohring engels.indd - Keramo Steinzeug

More documents

Recommendations

Info

high-capacity jacking pipe – e.g. DN 500 – is jacked using a stronger jacking system and the operationally necessary smaller piping then accommodated in it. Alternatively a so-called ”composite pipe” can be used. It consists of an inner pipe of the operationally necessary nominal size and a variable concrete or steel casing. Fig. 27 shows such a DN 400 / external diameter 860 mm vitrified-clay/reinforced concrete jacking pipe. Fig. 27: Vitrified-clay / reinforced concrete jacking pipe 6.6 Quality Safeguarding in Sewer Construction Under A 125 only specialist companies having experienced personnel and appropriate equipment may be entrusted with pipe jacking. Capability is deemed proven if the company holds an appropriate certificate from the quality partnership ”Quality Safeguarding in Sewer Construction”. The quality and testing stipulations include for micro-tunnelling the two assessment groups V3 and V2: V3 covers trenchless construction of sewers and drains in all materials ≤ DN 250. V2 covers trenchless and unmanned construction of sewers and drains in all materials and nominal sizes using controllable pipe jacking systems with automatic recording of jacking loads and continuous recording of positional deviation. In the General and Specific Requirements and with respect to companies’ equipment special experience and reliability of the companies and personnel deployed and controllable pipe jacking plant are required, amongst other things, in the quality and testing stipulations for both groups. The requirements must also be met by subcontractors. In April 1998 Quality Safeguarding in Sewer Construction listed for assessment group V2 72 certified firms and V3 49 certified firms. Micro-tunnelling Page 23 Another 19 applications were to hand. Clients have thus a wide choice of competent firms, facilitating the necessary competition. In keeping with the requirements of A 125 and proficient performance, clients should incorporate in the supplementary contract terms the following text conforming to VOB: Bidders must provide proof of the requisite specialist skill, operative capability and reliability and also a quality-assurance system comprising outside and self monitoring. The requirements of RAL quality and the GZ 961 testing rules must be fulfilled. Proof is deemed given if the company holds the appropriate RAL Quality Mark of the quality partnership ”Quality Safeguarding in Sewer Construction”. Alternatively an outside monitoring agreement for the individual operation concerned may be submitted; the requirements of the RAL quality and testing rules must be met. Because of the difficulty of thrust-boring operations their requirements are quite exceptional, including relevant knowledge possessed by only a limited number of sewer-construction companies. A glance at the number of certificates awarded in the last 10 years – since the quality partnership ”Quality Safeguarding in Sewer Construction” was formed – substantiates this. 1236 certifications for the assessment groups A1 and A2 in public sewer construction contrast with a total of 169 certificates for unmanned and manned thrust boring. The recommended form of competition for jacking-work contracts is therefore a Limited Invitation to Tender following a public eligibility competition.
Page 24 Micro-tunnelling 7. Cost-effectiveness There is still a widely-held opinion that trenchless sewerconstruction methods are very expensive and are more economic than conventional sewer construction at great depth or for specific cases, if at all. This misconception, shared by many clients, is the reason why in some regions there has not yet been any competition at all between the two construction methods. Micro-tunnelling may have long since proved itself in some key areas as the more economic alternative and shows continuous overall growth rates in Germany; but it still does not get the attention it deserves by virtue of its technical scope and environmental benefits. Costs for sewer construction depend on local circumstances, regulatory requirements and many constraints. The price level at the time, companies’ available capacity and the state of the economy play a part. It is therefore impossible to make any generally valid statement about costs for all regions. The most reliable way of finding the most cost-effective solution is to specify projects in alternative versions. If this is done over a period, a reliable picture of the market situation is obtained and assessment of when which construction project can be initiated more cost-effectively made possible. Nevertheless the large number of projects commissioned and carried out in Berlin permits some statements and a comparison with open construction to be made. These statements are representative and the trends implicit in them can be transferred. On the basis of 1997 and 1998 tender prices costs have been compared below between open construction and micro-tunnelling in 4 examples. For the cost-effectiveness comparisons to be placed in the context of the present study the following constraints limiting the calculations have had to be laid down: – All figures relate to construction above the groundwater. For projects in the groundwater costs would shift even further in favour of micro-tunnelling. – Installation of vitrified-clay pipes conforming to DIN EN 295 in nominal sizes DN 200, 250, 300, 400, 500, 600 and 800 is considered, at depths of 1.75, 3.00, 4.00 and 5.00 metres. In the diagrams intermediate depths have been interpolated and depth 6.00 metres shown by extrapolation. – The surface in the examples: unpaved (Fig. 28) interlocking paving bedded in gravel (Fig. 29) concrete paving (Fig. 30) bitumen paving (Fig. 31). Other stipulations: – minimum trench width as per DIN EN 1610 – soil excavated as average for classes 3, 4 and 5 – 50% soil replacement, i.e. import of backfil material to ensure proper compaction – spacing of manholes: 60 metres – water-permeability test for all sewers and manholes – width of the strip to be taken up on either side of the trenches before final restoration of the roadway as per Supplementary Technical Regulations for Line-Construction Work (ZTVL) – routing plan (open construction): in each section 6 junctions and connectors at each of the manholes – routing plan (micro-tunnelling): reinforced concrete starting and target shafts, spacing: 120 metres. Starting shafts for jacking ≤ DN 300 with 2.00-metre internal diameter, steel-plate cofferdam (liner plates) in the upper section, for target shafts in ≤ DN 300 jacking of steel-plate cofferdam (liner plates) with internal diameter 2.00 metres. Starting shaft converted into manhole as per Fig. 21. Starting and target shafts for jacking ≥ DN 400 of reinforced concrete with internal diameter 3.20 metres, steel-plate cofferdam in upper section (liner plates). Inner manhole as per Fig. 23. If the cost shares of open sewer construction are analysed, soil excavation plus sheeting work, soil replacement, refilling and compaction of soil and removal of the trench sheeting, together with breaking-up and restoration of the road surface are the significant elements. With increasing depth the share for the trench rises and to approximately the same extent the significance of reconsolidating the road surface falls. Delivering and laying the pipes and making the manholes are of secondary importance. In enclosed construction the actual jacking process including jacking pipes always predominates – largely irrespective of nominal size, depth and surface consolidation – with a cost share of over 60 to 70%. Then come the starting and target shafts at 25% of total costs at most. Innovative solutions for constructing the components in the starting and target shafts, and also increased jacking distances and utilisation of the greatest operationally justifiable lengths between manholes might effect savings here. A relatively subordinate role is played by the costs for integrated manholes and, as expected, the costs for opening-up and restoring surfaces are virtually insignificant. The 4 diagrams show in terms of cost the relative independence of jacking on the sewer’s depth. Each intersection of the assigned curves denotes equality of
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: Page 22 Micro-tunnelling - 6 classe
Page 27 and 28: Page 26 Micro-tunnelling 7.2 6000 5
Page 29 and 30: Page 28 Micro-tunnelling 7.4 7000 6
Page 31 and 32: Page 30 Micro-tunnelling 7.6 Social
Page 33: Page 32 Micro-tunnelling 6. For eve

mohring engels.indd - Keramo Steinzeug

Create successful ePaper yourself

Delete template?

Save as template?