620 Ingenieurwissenschaften und zugeordnete Tätigkeiten
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The German Code ATV-M 127-2 published in 2000 for the design of linings to rehabilitate sewers has proved itself a helpful guideline to find the optimum wall thickness of any liner material, e.g. CIPP or stainless steel sleeves. Many rehabilitation projects in different European countries have been performed successfully using this code. The code differentiates between three host pipe states: State I for untight sewers without cracks, state II for sewers with longitudinal cracks but a stable soil pipe system and state III for cracked pipes with larger deformations and considerable risk to collapse in the near future. State II sewers but installed close to the traffic surface must be calculated as a state III situation too. According to the code stress, deformation and stability tests are necessary. For many practical cases charts with stress factors and imperfection reductions allow to design without a computer. Numerous theoretical and experimental papers are available which mainly deal with circular linings. An evaluation of design codes carried out by experts of different countries shows a fairly good coincidence of the required wall thicknesses, but the assessment of pipeline damages by engineers is sometimes resulting in quite different assumptions necessary for the design input parameters. The paper reports about the progress in liner design since the 1st edition of the code. Additional clauses have to be introduced into the 2nd edition for non circular geometries (e.g. for hood and rectangular profile), imperfections describing practical and theoretical situations and new applications (e.g. railway crossings). International discussion can be useful to find safe and resources saving constructions.
With the assessment of sewers and drains generally recognised criteria such as tightness, stability, hydraulic capability and efficiency are valid. For the assessment of the stability, however, there are often uncertainties. In this connection the ATV-DVWK Advisory Leaflet ATV M 127-2 represents a practical development of the system of rules and standards for the stability of earth-bedded pipelines that is called upon in the case of dimensioning for rehabilitation procedures. Nevertheless, further assumptions about the pipe-soil system are necessary which often are based on individual appraisals and experiences of the designer. To that end, in the years 1999 to the beginning of 2002, extensive experiments and theoretical investigations were carried out at the Universities of Bremen and Muenster as well as at the Bremen hanseWasser GmbH in order to assess more reliably the load-carrying capacity in particular of damaged host pipes in the ground. The research was supported by the Federal Ministry for Education and Research (BMB+F) under the short title ASSUR. The paper gives a view of the essential contents of the research; further information can be taken from the final report to ASSUR.
In the German design code ATV-M 127-2, three host pipe states are differentiated: State I for leaky sewers without cracks, state II for sewers with longitudinal cracks but a stable soil pipe system, and state III for cracked pipes with larger deformations and considerable risk of collapse in the near future. State II sewers that are close to the traffic surface must be calculated as a state III situation. On the other hand, the US Standard ASTM F 1216 defines two states: structurally safe and fully deteriorated sewers. This paper examines the common aspects and differences between the two codes. A simple non-linear numerical approach is presented to evaluate the actual safety of the host pipe-soil system based on the following parameters: 1. the pipe material (e. g. age, corrosion depth, state of the contact zones), 2. the measured or estimated pipe deformations, 3. the soil group, stiffness, and possible voids occurring next to the springlines of the pipe, 4. the loading to be applied on the deteriorated pipe-soil system. Using stability and ultimate stress criteria, the safety of the system can be defined in a rational way. Missing parameters have to be introduced into the algorithm conservatively. Case studies are presented to demonstrate safe estimations for the host pipe state. The consequences on the required wall thickness of a lining and the application of non-circular linings are shown. The wall thicknesses resulting from a design for the fully deteriorated state as defined by the design codes in both the USA and Germany are compared and discussed.