Field CBR Test(IS 2720 Part 31)
In-situ California Bearing Ratio testing of subgrades and granular layers per IS 2720 (Part 31) — measuring the bearing value of the layer as it actually exists, in its true density and moisture state.
What is the Field CBR Test?
Laboratory CBR tests a remoulded specimen; the field CBR per IS 2720 (Part 31):1990 tests the ground itself — plunger penetration against a loaded reaction directly on the in-place layer, capturing its actual density, moisture and structure. That makes it the honest check where lab-to-field correlation is in doubt: existing roads being widened, layers compacted months earlier, moisture-sensitive subgrades, and forensic investigations of failed pavements.
Global Lab mobilises the standard penetration assembly with calibrated proving ring and surcharge weights, runs the test at prepared points on the layer, applies the standard-load computation at 2.5mm and 5mm penetration, and reports field CBR values point by point with layer moisture and density companions where sampled.
How the Field CBR Test is Conducted
- 1
Test Point Preparation
The layer surface is exposed, levelled and cleaned; the reaction load is positioned over the point. - 2
Assembly Setup
The standard plunger, calibrated proving ring and surcharge weights are assembled plumb over the prepared surface. - 3
Seating & Penetration
After the standard seating load, the plunger is driven at 1.25mm/min with load readings at the prescribed penetrations. - 4
Curve Correction & CBR Computation
The load-penetration curve is corrected where required; CBR is computed at 2.5mm and 5mm against standard loads and the governing value reported. - 5
Companion Measurements
In-situ density and moisture content are determined adjacent to the point where specified. - 6
Reporting
Point-wise field CBR values, curves and companions are issued via Autovity QLMS.
Applicable Test Standards
| Standard | Title | Scope | Type |
|---|---|---|---|
| IS 2720 (Pt 31):1990 | Methods of Test for Soils — Field Determination of California Bearing Ratio (Reaffirmed) | Test Method | Indian Standard |
| IS 2720 (Pt 16):1987 | Methods of Test for Soils — Laboratory Determination of CBR (Reaffirmed) | Laboratory Companion | Indian Standard |
| IRC:37-2018 | Guidelines for the Design of Flexible Pavements | CBR-Based Design Use | IRC Code |