GEOTECHNICAL

Proctor Compaction Test

Lab test giving the soil compaction curve (OMC + MDD)

Also calledproctor testproctor compactionstandard proctormodified proctorcompaction test
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CODES
IS 2720
Definition

The Proctor compaction test determines the relationship between a soil's dry density and its moulding water content under a standard compaction effort, producing the compaction curve whose peak gives the Optimum Moisture Content (OMC) and Maximum Dry Density (MDD). IS 2720 Part 7 is the Light (Standard) Proctor — 2.6 kg rammer, 310 mm drop, 3 layers × 25 blows; Part 8 is the Heavy (Modified) Proctor — 4.9 kg rammer, 450 mm drop, 5 layers × 25 blows — used where heavier field plant or higher specified densities apply (highways, airfields).

The lab MDD/OMC become the field control benchmark: earthwork is compacted near OMC to a specified percentage of MDD and verified by field-density tests. Choosing the right effort (Standard vs Modified) matters — specifying field compaction against the wrong reference density is a common cause of disputes.

Where used
  • Establishing OMC + MDD for earthwork control
  • Embankment, subgrade + backfill specification
  • Earth-dam + reservoir-bund design
  • Borrow-area material qualification
  • Selecting compaction plant + number of passes
Acceptance / threshold
Run per IS 2720 Part 7 (Standard) or Part 8 (Modified) as specified. The resulting MDD/OMC define field acceptance — e.g. ≥95-98% of MDD at OMC±2% per project/IRC/MORTH.
Frequently asked
What is the difference between standard and modified Proctor?
Modified Proctor (IS 2720 Part 8) uses a heavier rammer, greater drop and more layers/blows than Standard Proctor (Part 7), giving a higher MDD at a lower OMC — used where heavier compaction plant or stricter densities are required.
What does the Proctor test give?
The compaction curve of dry density vs water content, from which the Optimum Moisture Content and Maximum Dry Density are read — the control values for all field earthwork compaction.
Related terms
IS 2720 — Parts List (Methods of Test for Soils)
Complete list of all 19 parts of IS 2720 — methods of test for soils.
Consolidation Test (Oedometer)
Lab test giving compressibility + rate of long-term clay settlement
Maximum Dry Density (MDD)
Highest dry density a soil reaches at OMC for a given compaction effort
Optimum Moisture Content (OMC)
Water content at which a soil reaches its maximum dry density on compaction
Field Density Test
On-site test of achieved compaction (sand-replacement / core-cutter)
Soil Permeability Test
Measures the coefficient of permeability k governing seepage + dewatering
Soil Classification
Per IS 1498 / Unified Soil Classification System
Cohesion & Friction Angle
Mohr-Coulomb shear-strength parameters. Clay: cohesive (c). Sand: frictional (φ). C-φ soil has both.
California Bearing Ratio (CBR)
Subgrade strength index for pavement design
Effective Stress
Stress carried by the soil skeleton — total stress minus pore water pressure