Abstract: A composite manhole unit comprising a plastic inner element and an outer skeletal frame made of a structural material is provided. The plastic inner element is fitted within the skeletal frame, leaving large sections of the plastic inner element exposed. The exposed plastic sections can be readily cut in the field as necessary for attaching inlet and outlet pipes. A plurality of manhole units may be combined and assembled in a stacked manner to form a manhole system. The plastic pipe sections are sealed or connected to each other in a water-tight manner while the skeletal frame of the respective manhole units rest upon each other. The skeletal frame provides the structural support for the manhole unit and system. The excessive weight of the system and each respective manhole unit is reduced by using the skeletal frame in combination with the plastic inner element. The plastic inner element protects the skeletal frame from the corrosive atmosphere within, for example, a sewer system.

Abstract: A section of pipe includes a first body of material disposed in a bell and spigot pipe configuration having a bell portion extending to a bell end, which bell portion defines a radially inwardly facing annular seal groove in which to place a sealing ring to be engaged by a spigot portion of another section of pipe inserted into the bell portion. The seal groove is disposed between first, second, and third circumferentially-extending surfaces, the first surface facing radially inwardly and extending axially between the second and third surfaces, the second surface facing axially toward the bell end and extending radially inwardly from the first surface, and the third surface facing axially away from the bell end and extending radially inwardly from the first surface on an inclined away from the bell end as it extends from the first surface.