1. Cantilever abutments rely on soil strength, which is unreliable in loose sand
2. Gravity abutments require more concrete but leverage mass for stability
3. Cantilever abutments resist sliding better in loose soil conditions
4. Gravity abutments reduce lateral loads by redistributing them to the deck

Explanation

Explanation: Gravity abutments resist lateral loads (e.g., from an arch or earth pressure) through their mass, minimizing dependence on loose, sandy soil’s weak cohesion—unlike cantilever abutments, which rely on soil pressure and can tip or settle if sand’s shear strength fails under high forces. Gravity designs do use more concrete (B), but this supports their stability, not economy. Cantilever abutments don’t excel at sliding resistance in loose soil (C), and load redistribution to the deck (D) isn’t their role.

Learning Resources

• Review FHWA’s Geotechnical Engineering Circular No. 6 (2002) for abutment design in weak soils; CHBDC S6-19, Section 6.6 offers related guidance on shallow foundations and abutments.
• Explore the San Francisco-Oakland Bay Bridge (1936) west span for gravity abutment use.
• Tip: Consider cantilever abutments above 10-15m height for cost-effectiveness.