Abstract: This invention relates to a radially expandable locking sleeve device and to a gasket apparatus for providing a fluid tight seal between a pipe and a porthole in the wall of a manhole riser. The gasket is in the form of a tubular element of elastomeric material. An annular recess is provided in the inner surface of the gasket near one end for receiving a radially expandable split sleeve having interlocking end portions. The outer circumferential surface of the locking sleeve is so arranged as to continue uninterruptedly across the area of the interlocking end portions, and the end portions when engaged lock against both lateral displacement and circumferential collapsing of the sleeve.