Structural behaviour of closely packed sewer linings

Abstract

Sewer rehabilitation is becoming a subject of major importance to structural designers working in the field of public health engineering. This increasing interest has led to this comprehensive study on the various aspects of sewer lining as a means of sewer renovation. This research work is devoted to the parametric study of the structural behaviour of various closely packed sewer linings. The literature review has shown that, other than egg-shaped sewers, there is a general lack of information available as to how lining technology can be made available to the renovation of sewers of different shapes and sizes. As the shapes of sewer linings are primarily governed by the shape of the sewer in which the lining is to be inserted, the various shapes of sewers, presently under going construction or constructed in the past, form the core of the investigation. These include egg shaped, inverted egg shaped, horseshoe shaped, semielliptical shaped and the circular shaped _ the most widely used sewer shape in Bangladesh and overseas - sewers. The effects of various restraint conditions which simulate different probable temporary support systems during installation of the lining and different loading configurations which may arise at different stages of grouting have also been observed. Covering the feasible range of geometric, material and loading parameters, comprehensive design curves are presented based on the allowable stress- and deflection-limit criteria specified in the sewerage rehabilitation manual for all the above mentioned lining shapes except for the circular one. Substantial investigations have also been performed on the behavior of circular lining during installation. As expected, the main failure .criteria, for circular sewer linings, under grouting load has been found to be. buckling. Design recommendations, based on direct stress-limit criteria derived for a: hinged arch, have been proposed for circular linings subjected to hydrostatic pressure under different restraint set-ups. A comparison between various types of restraints has led to enhancement factors for the permissible grouting pressure, or alternatively, to reduction factor~ in terms of lining thickness which could be used in designing lining systems. Finally, with the help of the proposed deign curves and equations, an illustrative design example of each of the lining shapes has been carried out ..