Abstract: An improved pipe construction is disclosed having an inner and outer surface, intermediate walls having a top and bottom, and a plurality of primary internal cells. Each of the primary internal cells has a cell surface wall, collapsible ribs attached to the intermediate walls, collapsible apertures positioned on opposite sides of the intermediate walls and apertures, and internal flanks. Each of the collapsible apertures has an inner wall surface, with each inner wall surface having a deformable surface portion. Each of the end apertures is positioned between the collapsible apertures and primary internal cells. Each of the end apertures has an inner wall surface. The internal flanks are positioned intermediate the end apertures and the collapsible apertures. A method of forming the pipe of this structure is also disclosed.

Abstract: A manhole cover comprises a top having a top surface and an edge portion, a depending portion having a sidewall and a bottom surface, and an interior chamber. The manhole cover is fabricated from a first material, while the interior chamber is at least partially filled with a second material. The manhole cover preferably includes recessed handles which are recessed into the top and extend downwardly through the bottom surface. Cooperative engagement means in the form of inter-fitting indentations and protuberances are provided in the top surface and the bottom surface respectively. The bottom surface includes a first surface portion which includes a peripheral edge portion and a bracing portion. The bracing portion includes a plurality of brace members each of which have a lower brace surface and a brace sidewall.