Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 Page 13 Page 14 Page 15 Page 16 Page 17 Page 18 Page 19 Page 20 Page 21 Page 22 Page 23 Page 2413 An introduction to pipe jacking and microtunnelling 4 DESIGN AND CONSTRUCTION METHODS 4 Design and construction methods Prior to embarking on a detailed construction design and method analysis, the project engineer will generally have ascertained the basic design parameters to meet the requirements of the scheme. For a sewerage system these are likely to include: • Hydraulic requirements • Structural integrity • Drive lengths and alignment • Manhole requirements • Depth • Gradient Following an assessment of engineering, environmental and cost parameters, pipe jack excavation method and shaft construction will also be governed by a number of factors which include: • Ground conditions • Details of existing services and underground structures • Location of manholes and working areas • Lengths required • Diameters of pipeline • Economics Ground conditions will play a major role in determining the type of shaft to be constructed, the pipe jack excavation method and any ground support systems to be used. Each of these may have limitations in terms of either the diameter or length of drive. The interface between these variables, together with physical considerations, such as the location of manholes and the size of working areas, will provide an optimum solution or range of solutions which can then be appraised on the basis of cost and value engineering. When considering the use of pipe jacking as an alternative to open cut, an assessment of the advantage of realignment should be made. This may shorten the overall length of the pipeline.