California Bearing Ratio

California Bearing Ratio
(IS 2720 Part 16 — Pavement Design)

Laboratory determination of the California Bearing Ratio (CBR) of soils and compacted granular materials — the primary subgrade strength parameter for flexible pavement thickness design per IRC 37.

Overview

What is the California Bearing Ratio (CBR) Test?

The California Bearing Ratio (CBR) measures the bearing strength of a soil or pavement layer relative to a standard crushed stone base. A cylindrical plunger (50mm dia) is pushed into a compacted soil specimen at 1.25mm/min; load at 2.5mm and 5.0mm penetration are expressed as percentages of standard loads (13.44kN at 2.5mm; 20.16kN at 5.0mm) to give the CBR value. The higher of the two penetration CBR values is reported.

Conducted as per IS 2720 Part 16, laboratory CBR is tested at specified compaction (light or heavy Proctor, standard or modified) and soaking conditions (4-day soaking simulating worst monsoon case) for highway and airfield pavement design per IRC 37. Global Lab conducts CBR tests with NABL-calibrated load frames and automatic data logging for accurate load-penetration curves.

4-Day Soaked CBR

Standard CBR for highway design per IRC 37 — soaked for 96 hours before testing.

Light & Heavy Compaction

Both standard Proctor (IS 2720 Pt.7) and modified Proctor (Pt.8) compaction available.

Automatic Load-Penetration

Digital load cell and LVDT — automatic data logging of full load-penetration curve.

Swell Measurement

Swell during 4-day soaking measured for expansive soil subgrade assessment.

NABL Certified Reports

All test and calibration results are backed by traceable measurements and standardized procedures..

IRC 37 Pavement Design

CBR value directly used in IRC 37 flexible pavement thickness design charts.

Test in Action

California Bearing Ratio (CBR) Test — Site Images

CBR Mould Compacted at OMC — 4-Day Soaking Setup

CBR Plunger Penetration at 1.25mm/min

Load-Penetration Curve at 2.5mm and 5.0mm

Test Procedure

How the California Bearing Ratio (CBR) Test is Conducted

1

Sample Preparation & Compaction

Soil compacted in CBR mould (150mm dia × 175mm) in 3 layers per IS 2720 Part 16 at OMC from Proctor test.
2

Soaking

Compacted specimen submerged in water for 96 hours (4 days). Swell measured by surcharge weight and dial gauge.
3

Load Application

CBR plunger (50mm dia) penetrated at 1.25mm/min. Load recorded at every 0.5mm penetration to 12.5mm.
4

CBR Calculation

CBR at 2.5mm = (load at 2.5mm / 13.44kN) × 100. CBR at 5.0mm = (load at 5.0mm / 20.16kN) × 100. Higher value reported.
5

IRC 37 Design CBR & Report

CBR plotted on load-penetration curve. IRC 37 design subgrade CBR reported. NABL report within 7 days.

Standards & Specifications

Applicable Test Standards

Standard	Title	Scope	Type
IS 2720 Part 16	Methods of Test for Soils — Laboratory Determination of CBR	CBR Test	Indian Standard
IRC 37	Guidelines for the Design of Flexible Pavements (5th Revision)	Pavement Design	IRC
MORTH	Specifications for Road and Bridge Works — Subgrade and Sub-base	Highway Spec	MORTH
ASTM D1883	Standard Test Method for California Bearing Ratio (CBR) of Laboratory-Compacted Soils	CBR Standard	ASTM

Applications

Where is the California Bearing Ratio (CBR) Test Used?

Highway subgrade CBR for NHAI and state PWD flexible pavement thickness design

Airport runway and taxiway subgrade strength determination per AAI requirements

Industrial road and logistics park pavement design subgrade CBR

Railway formation subgrade CBR assessment for RDSO specifications

Granular sub-base (GSB) CBR verification per MORTH Clause 401

Embankment fill material CBR for pavement design over soft subgrade

Why Choose Global Lab

Our Advantages

NABL Accredited ReportsLegally valid IS 2720 Part 16 CBR certificates for IRC 37 pavement design.

Automatic Data LoggingDigital load-penetration curve — no manual reading errors.

IRC 37 Design FormatCBR reported in format directly usable in IRC 37 pavement thickness design.

Combined Pavement PackageCBR + Proctor + Atterberg + PSD as complete subgrade characterisation.

Pan-India CoverageGeotechnical lab at all 7 NABL-accredited locations.

Fast 7-Day Report4-day soaked CBR test and NABL report within 7 days.

California Bearing Ratio(IS 2720 Part 16 — Pavement Design)