Investigating the maximum soil pressure on a concrete pipe with poor haunch support subjected to traffic live load using numerical modelling

The behaviour of rigid pipes during backfilling, under soil weight, and under traffic live loads has received considerable attention from researchers in the past. A significant number of numerical, laboratory, and full scale studies on the response of rigid pipes under these effects have been published, which provide clear guidelines for the likely behaviour of the pipe. However, these studies were conducted assuming full support for the pipe in the haunch zone, although proper haunch support is, in fact, difficult to achieve in practice. This study therefore focuses on the effect of poor haunch support on the maximum soil pressure developed on a buried concrete pipe under traffic live loading using three-dimensional finite element modelling. The Duncan-Chang hyperbolic soil model has been used to represent the soil material and the pipe behaviour is simulated with a linear elastic model. The live load considered in the analyses is based on the British Standard design requirement (two axles with a maximum axle load of 450 kN). The poor haunch support has been modelled by removing the soil elements in the haunch zone to simulate the worst case scenario. The results show that the effect of poor haunch support causes significant increases in the maximum soil pressure and has considerable implications for the design of rigid pipes.