1. Shallow foundations can’t support heavy bridge loads near water
2. Scour undermines shallow foundations, threatening pier stability
3. Deep foundations are cheaper to install in riverbank conditions
4. Shallow foundations increase scour by obstructing water flow

Explanation

Explanation: Scour erodes soil around piers during floods, undermining shallow foundations and risking collapse as support vanishes—deep piles reach below scour depth (estimated via tools like HEC-RAS) into stable soil or rock. Shallow foundations can handle loads elsewhere (A), but not scour; cost (C) favors shallow without this risk; flow obstruction (D) isn’t significant.

Learning Resources

• Review FHWA’s HEC-18 (5th Edition, 2012) for scour depth estimation techniques; CHBDC S6-19, Section 6.4 provides scour analysis provisions
• Explore the 1993 Hatchie River Bridge collapse as a scour failure case study.
• Tip: Use riprap and monitoring for scour protection.