A contractor discovers that the soil bearing capacity at a job site is 2,000 psf, but the foundation design requires 3,000 psf. What is the most appropriate solution?
Correct Answer
C) Use a deeper foundation or soil improvement methods
When soil bearing capacity is insufficient, the foundation must be redesigned to reach more competent soil at greater depth or soil improvement methods must be used. Simply increasing width may not be sufficient for such a significant capacity difference.
Why This Is the Correct Answer
CORRECT_ANSWER - When soil bearing capacity is significantly insufficient (2,000 psf vs required 3,000 psf), the foundation system must be fundamentally redesigned. Deep foundations like piles or caissons can transfer loads to more competent soil layers below, or soil improvement methods like compaction grouting can increase the bearing capacity. This addresses the root problem rather than attempting inadequate workarounds that could lead to structural failure.
Why the Other Options Are Wrong
Option A: Proceed with construction and monitor for settlement
This is extremely dangerous and violates engineering principles. Proceeding with construction when soil capacity is 33% below requirements would likely result in excessive settlement, structural damage, or foundation failure. Monitoring settlement after the fact doesn't prevent the underlying problem.
Option B: Increase the foundation width to reduce bearing pressure
While increasing foundation width reduces bearing pressure, the capacity deficit is too large (50% increase needed). The required width increase would be impractical and may not fit within property boundaries or building constraints. This approach also doesn't account for potential settlement issues.
Option D: Reduce the building load by changing materials
Reducing building loads by changing materials addresses the symptom but not the fundamental soil capacity issue. The load reduction required would likely compromise the building's intended use and may still not be sufficient to bridge the 1,000 psf capacity gap safely.
Memory Technique
Think 'DIG DEEP' - when soil capacity is Deficient, you must go deeper with piles/caissons or Improve the Ground through soil modification rather than surface band-aids.
Reference Hint
Florida Building Code, Chapter 18 (Soils and Foundations) and IBC Chapter 18 for soil bearing capacity requirements and foundation design criteria
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