When a drainage system (i.e. u-channels with catchpits) is connected to a main drainage channel, a segment of short pipe is used. What is the reason of such arrangement?

In scenarios where drainage systems intersect, engineers encounter three primary connection arrangements:

1. New system connected to an existing channel: This setup often necessitates careful consideration of potential differential settlement between the new and established structures.
2. Existing system connected to a new channel: Significant differential settlement is highly probable in this scenario, posing a risk of damage to the connecting concrete pipes.
3. New system connected to a new channel: While both structures are new, settlement variations are still possible, especially if soil conditions are not uniform.

Regardless of the scenario, engineers prioritize assessing the total differential settlement or lateral movement expected between the drainage system and the main channel. In cases (b) and (c), where significant settlement is likely, a strategic solution is implemented: a series of short pipes are incorporated into the design. These short pipe segments act as flexible joints, allowing for movement and accommodating uneven settlement between the drainage system and the main channel. This flexibility safeguards the integrity of the connecting pipes, preventing cracks or failures that could compromise the entire system.

In essence, these short pipes act as a buffer, absorbing the stresses and strains induced by differential settlement. By incorporating this flexible element into the design, engineers ensure the long-term functionality and resilience of the drainage system, even in the face of ground movement.