Large Diameter PE Pipes for Combined Sewer Overflow Applications [PE]

Designers are increasingly choosing to attenuate the peak discharge from combined (storm plus sanitary) sewers, and from storm sewers alone, by providing local storage. This enables waste water treatment to occur once a storm event has passed and there is capacity available in the waste water treatment facility. In urban areas large diameter ‘hydraulically oversized’ sewers are sometimes used to provide this local attenuation storage. To reduce the footprint of the installation, designers select large pipe sizes with significant burial depths and minimal spacing between parallel pipe runs. Large Diameter Profile Wall PE Pipes are being increasingly selected for this application. This paper will examine the use of 2D and 3D FEA modeling tools to assess the suitability of these products in this application by a case study review. AASHTO’s NCHRP Report 631 notes that profile wall PE pipes often experience local wall buckling. It recommends that the assessment for burial should be based on a pipe cross sectional area where the locally buckled portion of the pipe wall is ‘subtracted’ from the cross sectional area. This paper examines the suitability of that recommendation.