Graphical design tools to determine the minimum self-cleansing slope in small diameter sanitary sewers

Abstract

This paper presents graphical tools for the design of sanitary sewers with self-cleansing by shear stress, for diameters between 100 mm and 400 mm, using two different criteria: first, using the assumption that under minimum flow the liquid will develop a shear stress equal to that generated by the sewer when running full at a velocity of 0.6, 0.7 and 0.8 m/s, and second, using self-cleansing shear stress of 0.867, 1.4, and 2 N/m2. These tools consist of curves to determine the self-cleansing slope, the depth-to-diameter ratio, the maximum flow rate that can be transported with a relative depth of 0.8D, and the velocity under part-full and full-pipe conditions for a given minimum flow rate. Also, equations are provided to determine both an approximate value of the self-cleansing slope, as well as the exact slope. A constant Manning’s roughness coefficient of 0.009 s/m1/3 was used, corresponding to new PVC pipes.

Keywords

• autolimpieza
• tensión de corte
• velocidad autolimpiante
• diseño
• alcantarillado sanitario