Discussion on Papers 20–23

DR E. B. GLENNIE AND MR G. M. A. JONES, WRC Engineering Centre

As has been recognized in Paper 20 the choice of suitable safety factors against failure of the brickwork is a particular problem of the approach suggested. It appears that the choice of appropriate safety factors could well be of greater significance than any inherent inaccuracies in the analysis. Considerable further research and validation work is necessary before the suggested approach becomes a working tool.

The WRC is looking at two methods of assessing brick sewers, comparing the permissible stress approach with one that considers the geometrical stability, and has tentatively concluded that for the smaller trunk sewers constructed from one or two rings of brickwork, the most common problem is geometrical instability caused by the lack of ground support. Erosion of the brick invert is also sometimes a problem. Overstressing of the brickwork has not often been observed in the limited number of cases we have studied.