Question

. A proctor test has been conducted and it was verified that the relative field compaction is 96.2%. Can we conclude that the in-situ conditions meet the compaction specifications?

Answer 1

NO, Because the 95% confidence rate.

  Proctor and company monitored settlement at the Bouquet Dams for 20 years and verified their hypothesis. Later, the modified Proctor method was developed to better represent the heavier compaction equipment that became available. In general, the modified Proctor works better with granular soils and the standard Proctor test is better with finer grained soils. Fine grained soils are susceptible to being over-compacted, resulting in pumping due to high pore pressures that can’t dissipate fast enough. The standard Method limits this potential since it uses less energy.

The standard Proctor test uses a 1/30cuft mold, with a 5.5lb hammer falling 12 inches, with three loose soil lifts, each compacted with 25 blows per lift, giving 12,400 ft-lbs of compactive energy per cubic foot of soil. In Proctor’s day, a sheepsfoot compactor was typically designed to produce about 100psi contact pressure, or about 14,400 ft-lbs per cubic foot of soil, at its maximum efficiency.

So by trial and error and a lot of empirical data, Proctor and others found that 90% of standard Proctor compaction gave about a 85% confidence rate that post construction settlements would be less than one inch for a foot of soil. At 95% standard Proctor compaction, there was a 95% confidence rate. And 90% modified Proctor, for many soils, is roughly about the same as 95% standard.