A 10-year-old trapezoidal monsoon drain was found cracked and damaged.
Damaged trapezoidal drain
From visual observation, defect may be caused by:
- Differential soil settlement below and on the sides of the trapezoidal drain. This causes drain structure to move unevenly. Results in crack of drain.
- Through these cracks, water seepages occur. The flow loosens and erodes the soil that supports the drain. Settlement increases with time.
Recommendation: To reconstruct the monsoon drain using precast U-drain.
1. Precast – quality of work can be controlled.
2. Shorter duration of work completion - faster speed of construction.
3. U-shape of drain requires less working space thus will not affect trenches and piping.
4. Drain also acts as retaining wall – provides soil stability from lateral movements.
1. Higher cost by 3.6% as compared to in-situ re-construction of trapezoidal drain.