Proctor Compaction Test, CBR Compaction

Soil Compaction Tests

Proctor Compaction Test
The Proctor Compaction Test, named in honor of Ralph Roscoe Proctor, is a laboratory method to determine maximum dry density of soil by determining the optimal moisture content at which a given soil will become most dense. The standard Proctor compaction test was first developed in 1933 and was later updated to create the modified Proctor compaction test. The test is commonly used for engineering applications globally to determine how on-site measurements compare with the Proctor test results in the determination of soil density.

The test consists of compacting soil of known moisture content into a cylindrical mold using controlled magnitude compaction. The soil is compacted into the mold in layers by receiving blows from a weighted hammer at a specific height. After repeating the process for different moisture contents, dry densities can be determined. A compaction curve can then be developed to show the exact relationship between the dry density and moisture content. Maximum dry density and the corresponding moisture content are then obtained, or the optimal moisture content.

This methodology and corresponding equipment is detailed in ASTM D698, “Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort”. Since the properties of soil will have immediate and long-lasting effects for engineering and structural integrity, accurate soil compaction tests remain critical to the geotechnical engineering and construction industries.

CBR Compaction Test (California Bearing Ratio)
Originally developed in the late 1920s by the California Division of Highways (now referred to as Caltrans and officially adopted in 1935), the CBR test was designed to ensure that highway pavements could economically carry the anticipated loads. The laboratory test is performed to evaluate soil subgrade strength and base course materials. Its many years of use and improvements have affirmed high reliability and accuracy for pavement engineering design.

As outlined in the ASTM D1883 specifications, “Standard Test Method for CBR (California Bearing Ratio) of Laboratory Compacted Soil”, the test is relatively simple and has established reliability for field correlations of flexible pavement thickness requirements. The values obtained from CBR compaction tests are used by the Federal Highway Administration, state Departments of Transportation and the Federal Aviation Administration.

Humboldt offers a complete line of soil compactors and molds for Proctor compaction testing, CBR and other types of soil tests. Our soil compactors and molds comply with ASTM testing standards such as ASTM D558, D559, D560, D698 and D1557.

Compactors include soil compaction hammers, automatic mechanical compactors, Proctor hammers, manual compaction hammers and accessories.

A variety of Proctor molds (standard and modified) are available in addition to CBR Molds and LBR Molds, along with swell plates, cutting edges and weights.

Vibratory compaction equipment, such as the Vibratory Compaction Frame and Hammer Set, and the Harvard Miniature Compaction Apparatus are also useful for a variety of moisture density tests.

If you have questions or need help selecting equipment, please call us at 1.800.544.7220 or use our Ask Humboldt form.