During construction of a new home, the contractor discovers expansive clay soil conditions. According to Michigan Building Code, what is the recommended foundation design modification?
Correct Answer
C) Install a deeper foundation with proper drainage
The Michigan Building Code recommends deeper foundations with proper drainage systems to mitigate the effects of expansive clay soils.
Why This Is the Correct Answer
Expansive clay soils swell when they absorb water and shrink when they dry, creating vertical movement that can damage foundations. The Michigan Building Code's recommended approach is to install a deeper foundation that reaches below the active zone of moisture change, combined with proper drainage systems (e.g., perforated drain tile, gravel backfill, waterproof membranes) to manage water away from the foundation. This combination addresses both bearing depth and moisture management.
Why the Other Options Are Wrong
Option A: Add steel reinforcement to standard footings
Adding steel reinforcement to standard-depth footings strengthens the footing against cracking but does not eliminate the root cause — soil movement due to moisture changes. A reinforced footing at standard depth will still heave and settle with expansive clay.
Option B: Use post-tensioned concrete slabs
Post-tensioned concrete slabs are a solution commonly used in arid climates (e.g., Texas, Arizona) for slab-on-grade construction over expansive soils. Michigan's climate and typical basement construction practices make this less applicable, and it does not address the basement foundation scenario described.
Option D: Increase footing width by 50%
Widening the footing by 50% distributes the load over a larger area to address bearing capacity issues, not expansive soil heave. Expansive clay's problem is volumetric change with moisture, not insufficient bearing capacity.
Memory Technique
Remember 'Deep + Dry = Safe Foundation in Clay': go deep enough to escape the moisture-active zone, and keep the clay dry with drainage. Two D's: Depth and Drainage.
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