Hydraulic capacity of 2in1 sewers
It is today possible to have an extra pipe installed in an existing sewer with traditional cured in place (CIPP) technology. Such an installation will affect the capacity of the sewer. The cross sectional area will decrease and the hydraulic radius will increase which decreases the capacity. The new liner will have a smother surface, which will increase the capacity of the sewer. The overall change of capacity of a sewer where a 2in1 liner has been installed was investigated. Traditionally the capacity of non-circular sections is calculated using the Colebrook-White equation with the diameter replaced with the hydraulic radius multiplied by 4. This approach can be questioned since this cross-section differs from other cross-sections normally calculated with this method, like egg-shaped or rectangular sections, through the introduction of an “obstacle” along the pipe. The validity of the Colebrook-White equation has been investigated using CFD-modelling. The results shows hat the traditional way of calculating the capacity of non-circular sections gives results on the conservative side and can be used for 2in1 pipes. In most cases the capacity of the sewer will decrease after installation of a 2in1 pipe, but this depend on several parameters and need to be investigated for each case.