What is an underdrain?

Answer: B — Perforated pipes routed along abutment

An underdrain is specifically designed as a system of perforated pipes that are installed along the abutments and other critical areas beneath bridges and roadways. The primary purpose of underdrains is to facilitate the movement of excess water away from the structure, thereby preventing saturation of the soil and reducing hydrostatic pressure that can lead to instability or damage. By collecting and channeling water away, underdrains help maintain the integrity of the bridge by mitigating the risks associated with subgrade moisture, which could lead to potential structural failures or complications in road performance. They are often used in conjunction with other drainage methods to ensure that water is effectively managed around the bridge and its foundation. Understanding the function of underdrains is crucial for ensuring the long-term safety and maintenance of in-service bridges.