California Bearing Ratio Prepared by Arunangsu Patra Under the Guidance of Prof. Jayashree Sengupta Department of Civil Engineering Sir J. C. Bose School of Engineering Supreme Knowledge Foundation Group of Institutions

INTRODUCTION: The behavior of road surface depends on the strength of the fill material and the subgrade below it. This strength of the subgrade soil is expressed as California Bearing Ratio (CBR) It was developed by California State Highway Department (USA) for evaluating the bearing capacity of subgrade soil for design of flexible pavement, before second world war. It is the ratio of test load to the standard load at a specified penetration by a standard plunger under controlled density and moisture conditions.

How the test is done: The test is performed by measuring the pressure required to penetrate a soil sample with a plunger of standard area. The measured pressure is then divided by the pressure required to achieve an equal penetration on a standard crushed rock material. And using the values obtained from the test from an empirical design chart, the pavement thickness are calculated.

classification: Laboratory Test Field Test

CBR LABORATORY TEST Specimen may be Mould Prepared In-situ 150mm diameter 127.3mm height Separate base plate A collar

APPARATUS USED: MOULD with COLLAR SPACER DISC & WEIGHTS RAMMERS

APPARATUS USED: (Contd.) WHOLE APPARATUS LOADING MACHINE

CBR Laboratory TEST SET-UP Proving Ring Dial Gauge To Measure Load Plunger 50mm DIA Dial Gauge To Measure Penetration Surcharge Weight, 147mm DIA Soil Sample Inner DIA of Mould, 150mm Base Plate

laboratory CBR TEST: procedure The specimen is soaked and the expansion is measured. Load is applied by the loading frame through a cylinder plunger of 50mm diameter and penetration is measured. Rate of penetration is maintained at 1.25mm/minute. Loads are recorded for 2.5 and 5.0mm. Load is expressed as a percentage of the standard load at the respective deformation level, and is known as the CBR value.

laboratory CBR TEST: procedure Load a piston at a constant rate See what load it takes to make it penetrate a known amount

CBR Equation x = material resistance or the unit load on the piston (pressure) for 2.5 mm or 5 mm of penetration y standard unit load (pressure) for well graded crushed stone. For 2.5 mm of penetration = 1370 kg For 5.0 mm of penetration = 2055 kg

CBR GRAPH

TYPICAL CBR VALUES Description of Material CBR Well-graded crushed aggregates 100 Well-graded natural gravels 80 Silty gravel or silty, sandy gravel 40-80 Well-graded sands, gravelly sands 20-50 Clayey gravel or sandy, clayey gravel 20-40 Silty or clayey sands 10-40 Fine clean sands 10-20 Lean (low-plasticity) clays, sandy clays 5-15 Silts, sandy silts Organic silts, lean organic clays 4-8 Fat (high-plasticity) clays 3-5

FIELD CBR TEST

FIELD CBR TEST: procedure

SCOPE FOR FUTURE WORK To incorporate stabilizers like cement, fly ash, rice husk ash, etc and To experimentally investigate the CBR improvement by using the above materials as stabilizers.

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