Which statement best describes the influence of proper subgrade drainage on slab performance?

• A. It reduces moisture-related problems and differential settlement.
• B. It increases moisture-related problems.
• C. It has no effect on slab performance.
• D. It only affects surface color.

Answer: (A)

Controlling moisture under the slab is essential because it keeps the bearing soil from becoming saturated and uneven. When drainage works well, water doesn’t pond beneath the slab, so the soil’s strength stays more uniform. That uniformity reduces differential settlement, since different parts of the slab aren’t settling at different rates due to varying moisture and strength. It also minimizes moisture-related issues like swelling, shrinkage, and related cracking or heaving, especially in expansive soils. So, proper subgrade drainage directly lowers moisture problems and helps keep the bearing capacity consistent, which is why this description best fits how drainage influences slab performance. It’s about drainage effects, not surface color, and it does affect slab behavior.