CONCRETE PIPE Manhole Barrels Manholes Joints and Gaskets A manhole barrel joint consists of a bell and spigot connection, just as with concrete pipe. A manhole gasket is provided with each manhole barrel, which is stretched around the spigot prior to connection. For manholes where hydrocarbons (i.e. oil and/or gas) may be anticipated, a nitrile gasket is recommended to withstand the potentially aggressive constituents that may be present. The maximum allowable depth of a typical precast manhole with regard to lateral earth pressure is in excess of 90 meters (300 feet) or, for all practical purposes, unlimited. Because of this, the critical or limiting factor for manhole depth is the supporting strength of the base structure or the resistance to crushing at the ends of the riser section. This phenomena, being largely dependant on the relative settlement of the adjacent soil mass does not lend itself to precise analysis. Even with extremely conservative values for soil weights, lateral pressure and friction coefficients, it may be concluded that more than 100 meters can be safely supported by the riser sections without end crushing, based on the assumption that provision is made for uniform bearing at the ends of the riser sections and the elimination of localized stress concentrations.1 1 Concrete Pipe Design Manual, American Concrete Pipe Association, 2001, Page 92 PAGE 42 LAFARGE PIPE eMANUAL