Eco-technique of sewer renovation using composite shells: structural analysis

Abstract

An eco-technical renovation of the sewage system is developed in this paper; this technique involves incorporating into the existing sewer a series of jointed prefabricated sandwich or composite shells. The purpose of his study is to determine the structural shell deflection, the high displacement areas and to validate the non-failure criterion for each ply constituting the inner and outer laminate facings. The numerical results were obtained at low cost by using the finite element method. Studies have focused on structural analysis of a typical shell unit with an ovoid form (egg-shaped section) when it is subjected, during annular space filling operation, to pressure forces generated by wet concrete. To ensure the safety of the composite shell structure, Tsai-Hill criterion function is applied and results are presented for the most stressed plies.Key words: sanitation; sustainable development; composite collector en composite; sandwich shell; finite element approach. INTRODUCTIONIn some large and older cities, the underground collectors of sewage were built with bricks and are now showing signs of ageing behaviour and fatigue [1][2][3]. This situation requires therefore particular attention to assess the sewer's structural state. In addition, J Fundam Appl Sci. 2011, 3(2), 144-154 145 Large underground drain-pipes are able to collect and remove wastewater and surface water from populated areas to sewage treatment works for water sustainability and advanced recycling (Fig. 1). But the inevitable leaks in the drainage system, mainly due to the ageing behaviour of such structures, the poor tightness and the fatigue phenomenon can pollute groundwater and therefore contaminate drinking water supplies and agriculture soils [6]. This environmental pollution can cause a number of risks to human health and the environment and becomes a source of several diseases such as diarrhea, typhoid, cholera, hepatitis, malaria [7]. Fig.1. Sewage systemIn order to overcome this problem and minimize or drastically reduce these risks, an innovative technique for the renovation of existing sewage systems is presented in this article. This technique involves incorporating into the existing sewer a series of jointed prefabricated composite shells [8]. The new shell cross-section is practically the same as the existing sewer with a small reduction in size. The reduction in the hydraulic crosssection is counterbalanced by the shell ultra-smooth surface which reduce friction to fluid flow [9]. In addition, the annular space (void) between the composite shell and the existing collector is filled with concrete [8,10].It should be noted that in the sanitation domain, the use of cross-section with an ovoid form (egg-shaped section) is highly recommended, because this shape prevents sedimentation phenomenon as a result of high-speed water with low flow in the narrow side of the collector (lower part of the shell). For that reason, a composite shell with an ovoid cross-section has been adapted to the current situation. Studies were ...