This article presents a part of UPC´s study about the sustainability analysis of 8 drainage pipes (four alternatives made concrete with 400 mm, 800 mm, 1200 mm and 2000 mm of diameter and four alternatives made plastic with the same diameters). MIVE’s methodology –Integrated Value Model Sustainability Evaluation- (Aguado, Manga and Ormazábal, 2006) was used in this study and a comparative analysis of sustainability index of each concrete alternative versus each plastic alternative was performed. In total 14 indicators which divided into 4 main areas: functional, economic, social and environmental were considered. This article focuses on two indicators that are evaluated in relation to structural design: the additional mechanical capacity and raw material consumption during execution. These two indicators are closely related especially when it comes to flexible pipes (Polypropylene, Polyethylene, Polyvinyl chloride). The structural capacity of flexible pipes is mainly given by the type of trench, and the type of land used for filling and compacting it. That is, any surface loading is resisted by the system of ground-structure interaction. The structural calculation was carried out following the German guideline ATV-127 (Guidelines for the mechanical calculation of pipes and sewage pipes). This guideline is used to study both flexible and rigid pipelines and it is implemented together with other guides in the Análisis Mecánico de Tuberías Enterradas program (AMTE). Additional mechanical capacity (capacity increase over specified capacity) of each pipe alternatives has been calculated based on several parameters: height of fill, fill type and degree of compaction of the fill. The conclusions reached once calculations have been performed with all the aforementioned constraints are the following: 1) The types of filling and compaction rate have an influence on the additional mechanical capacity of the pipe. This influence is enhanced when using plastic pipe because the land contributes 85% of the total resistance to ground-tube set on average. By contrast, in concrete pipes (rigid pipes) the land provides only a 15 % of the resistance. 2) The influence of filling and compaction rate increases with increasing the diameter of pipe.