While selecting a site for a major river bridge, a deep gorge with high rocky cliffs on both sides is being evaluated. Compared to a wide alluvial plain downstream, the gorge site offers a significant advantage in terms of
- ALower wind loads on the superstructure
- BReduced foundation scour depth and smaller span lengthCorrect
- CEasier access for construction equipment
- DLower temperature variation effects
Solution
Concept
Advantages of gorge sites in bridge site selection
Formula
NONE
Step-by-step solution
1. Compare a deep gorge with high rocky cliffs against a wide alluvial plain. 2. A gorge naturally narrows the river channel, requiring a much smaller span length and fewer piers. 3. The exposed or shallow bedrock in a gorge prevents significant bed scour, drastically reducing foundation depth compared to alluvial sandbeds. 4. Gorges increase wind channeling and present difficult equipment access, so only option B is a valid advantage. Answer: B
Explanation
Selecting a bridge site at a deep gorge with high rocky cliffs offers two major structural and hydraulic advantages: the rigid bedrock foundation minimizes or eliminates foundation scour depth, and the narrow gorge profile substantially reduces the required bridge span length and overall waterway requirement.
Why the other options are wrong
A) Gorges create a wind-tunnel effect, increasing wind loads on the superstructure. C) Steep rocky cliffs restrict physical access and make heavy machinery transport difficult. D) Ambient temperature fluctuations are not reduced by gorge topography.
Shortcut
Rocky Gorge = Narrow width (short span) + Solid rock bed (no deep scour).
Common mistake
Assuming gorges reduce wind load; in reality, gorges funnel winds and increase wind pressure on the superstructure.
Correct answer: B) Reduced foundation scour depth and smaller span length