Shaping element for manhole opening and gasket

A shaping element to define the inner surface of revolution of an opening through a wall of settable material as it is being formed between an exterior and an interior wall form, said shaping element comprising:

• exterior and interior mating parts, securing means to secure said mating parts in assembled position providing a peripheral wall configured to produce an inner surface of revolution of a desired size and shape, each of said parts having a longitudinal axis which is co-axial with said opening when the parts are assembled and each part having a peripheral flange with an outer end and an inner end, said outer end adapted to abut the respective wall forms, each peripheral flange extending inwardly from its outer end and each defining a part of said peripheral wall, the flange of said exterior part being substantially straight in section, the flange of said interior part being extended at its inner end by an extension of generally L-shaped cross-section having one leg forming a radially inwardly extending step transverse to said longitudinal axis and having the other leg extending generally parallel to said longitudinal axis, said other leg radially inwardly spaced from and lapping the inner end of said outer part, the inner end of said outer part being axially spaced from said step in the assembled position of said parts, the inner end of the flange of the outer part and said extension providing a peripheral channel of generally L-shaped cross-section to receive and retain the radially inward cross-sectionally angled sealing lip of an annular sealing gasket which has a radially outer anchoring portion adapted to radially protrude from said peripheral wall to be anchored in said settable material.