NICET - Highway Construction Inspection Practice Exam

What is the purpose of mechanically stabilized walls in bridge abutments?

1. To lower the cost of materials

2. To support the bridge seat on reinforced backfill

3. To minimize environmental impact

4. To replace traditional foundation systems

The correct answer is: To support the bridge seat on reinforced backfill

Mechanically stabilized walls (MSWs) in bridge abutments serve a crucial role in supporting the structure of the bridge, specifically by providing a stable foundation for the bridge seat. The MSW consists of alternating layers of soil and reinforcement materials like geogrids or steel strips, which help to create a strong and durable retaining structure. This design allows the walls to effectively manage lateral earth pressures and retain backfill material behind them, ensuring that the bridge seat — the part of the abutment that supports the bridge superstructure — is adequately supported. By facilitating proper load transfer and maintaining stability under various conditions, mechanically stabilized walls help mitigate issues that can arise due to settlement or shifting of the soil. This makes the bridge abutments safer and more reliable as they bear the weight of the bridge and any vehicular loads that pass over it. The inclusion of reinforced backfill enhances the overall structural integrity, contributing to the longevity of the bridge. Other choices, while they may have some relevance in different contexts of construction, do not specifically address the primary function of mechanically stabilized walls in this application.