CSLB General Building (B)Site Work, Foundations and ConcreteMedium
A geotechnical engineer performs a Standard Proctor compaction test on soil samples from a building pad. What does this test primarily determine?
- AThe percentage of expansive clay minerals present in the soil
- BThe soil's allowable bearing capacity in pounds per square foot
- CThe permeability rate of the soil for drainage design
- DThe maximum dry density and optimum moisture content for compaction
Show answer & explanationAnswer & explanation
Correct answer: D. The maximum dry density and optimum moisture content for compaction
The Proctor test compacts soil samples at varying moisture contents to determine the maximum dry density achievable and the optimum moisture content at which that density occurs. Field compaction is then specified as a percentage of this maximum (e.g., 90-95% relative compaction).
Why the other options are wrong
- A. Clay mineral content is assessed through mineralogical or Atterberg limit tests.
- B. Bearing capacity is determined by separate load-bearing tests, not Proctor testing.
- C. Permeability is measured with permeability/percolation tests, not Proctor testing.
Proctor Compaction Test
A laboratory test that determines the maximum dry density of soil and the optimum moisture content needed to achieve it, used as a benchmark for field compaction control.
- Standard and Modified Proctor tests use different compactive efforts
- Field compaction specs typically require 90-95% of maximum dry density
- Proper compaction reduces settlement and improves bearing capacity
Memory trick: Proctor finds the sweet spot of water and weight.