Design Methodology for High Density Polyethylene Manholes

Polyethylene manholes are used in piping systems for sewage, storm water run-off, landfill leachate, and industrial effluent. Many manholes are used in applications no more than a few feet deep, where loading is minimal and almost any vertical structure will work. However, for manholes of any significant depth and for manholes located below the groundwater level, substantial earth and groundwater loads may exist. Although often ignored, these loads can approach critical values for the manhole. Evaluation of the manhole, embedment and loading is a crucial task of the design engineer. This paper presents a design methodology that may be used for such applications.

The design methodology considers both the ring-directed and the axial-directed effects of the applied earth pressure. Ring loads subject the manhole wall to compressive strains which, if not limited, can cause buckling. These loadings are usually intensified by groundwater. Axial strains occur in the manhole wall due to the downdrag of the surrounding soil. Proper design limits axial strains and provides an adequate safety factor against buckling.