Chapter 3: Compaction

Maximum Dry Density Soils used in construction must be compacted. When compacting material water is needed as a lubricant to help the grains become closer, making the material denser.When too much water is added the dry density goes down.

Maximum Dry Density Standard Proctor Test 4” dia. mold with vol.= 1/30 cubic foot 5 ½ lb hammer with a 12” drop #4 material is compacted in 3 lifts with 25 blows of the hammer per lift Water is added and procedure repeated

Maximum Dry Density, cont. At each moisture content the weight of the soil in the mold is measured and a sample is taken for moisture content Plotting the dry density / moisture produces a graph resembling a bell curve Max. dry density and moisture content are obtained from the graph

Testing Procedures The Standard of the Industry is a Nuclear Density Gauge. The gauge inserts a rod containing radioactive material into the soil. The gauge measures the radiation returning from the tip of the rod to the base of the gauge providing density and moisture of the material.

Testing Procedures The results of density gauge are compared to the proctor of the material to determine relative compactive It is critical that the correct proctor values are used, if the wrong proctor is used results are invalid

Testing Procedures Sand Cone Method Sand calibrated for pounds per cubic foot Hole is dug into material to be tested Material from hole is weighed/moisture sample taken Sand is placed into hole to determine volume

Quality Control Compaction testing is required for: Subgrade Preparation Fill Material - usually tested per lift Backfill Material - usually tested per lift Roadbase Asphalt

Quality Control, cont. Contract documents specify the frequency of Quality Control Testing for compaction Quality Assurance Testing - Testing to confirm Quality Control Testing results are acceptable. Performed at lower frequency than Quality Control testing.

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