Wikipedia defines inertia as the resistance of any physical object to any change in its state of motion (this includes changes to its speed, direction or state of rest). It is the tendency of objects to keep moving in a straight line at constant velocity.
So, why is inertia important for buried sewerage structures? Without (lots of) inertia, pipes can become more easily dislodged from their intended position during and after installation.
- Most sewer pipes are jointed using a push-fit design where an elastomeric seal is compressed between the interlocking ends of two pipes being joined together. If the receiving pipe has low inertia and insufficient resistance to the jointing force applied from the pipe being laid, additional restraint may be required to hold the receiving pipe steady and to maintain the correct position while the pipe being laid is pushed home. This additional effort during installation can increase construction time and means that operatives are working in the trench for longer periods and can be subject to higher safety risk exposure.
- Backfilling and compaction. Pipe embedment should be placed and compacted evenly around the pipe to the correct specification. Unbalanced forces acting on each side of the pipe due to uneven backfilling and compaction can lead to a greater tendency for the displacement of pipes with low inertia.
- After installation, if the surrounding ground is subject to a high water table or if the ground is saturated, for example during a flood, pipes of low inertia are at greater risk of flotation. Take a look at the video below demonstrating a stunning failure of a corrugated steel culvert in Maine State, USA due to flotation during a flood. In known areas of flood risk or high groundwater levels, resistance to flotation can be designed into the installation for low inertia pipes, at extra cost and requiring a more complex, longer installation time.
Why does concrete outperform other pipeline materials?
Concrete is the Heavyweight Champion of the drainage world. The intrinsic self-weight of concrete provides high inertia to pipeline systems and a natural resistance to being moved out of position during jointing, backfilling, compaction and against flotation.
High inertia concrete pipes are the only sensible choice for a strong, stable, robust and durable wastewater pipeline system.