California Bearing Ratio Test Equipment

CBR Machine – California Bearing Ratio Test Equipment

The CBR Machine (California Bearing Ratio Testing Machine) is a motorised, load-frame instrument used to determine the bearing strength of subgrade soils, sub-base, and base course materials for road and runway pavement design. The CBR value is the key input for pavement thickness design as per IRC:37, MoRTH, and AASHTO methods.

What is CBR Value?

CBR (California Bearing Ratio) is the ratio of the load required to cause a standard plunger (50 mm dia) to penetrate a soil specimen at a defined rate, compared to the load required for the same penetration in a standard crushed stone material. Higher CBR = stronger subgrade.

• CBR < 3%: Very weak subgrade — heavy pavement required
• CBR 3–7%: Moderate — typical Indian highway subgrade
• CBR 7–20%: Good — suitable for lighter pavement sections

CBR Machine Specifications

• Capacity: 50 kN (standard) — 100 kN (heavy duty)
• Plunger: 50 mm diameter, 75 mm stroke
• Penetration rate: 1.25 mm/min (motorised, constant speed)
• Load measurement: Proving ring or load cell (digital/analog)
• Deflection measurement: Dial gauge (0.01 mm LC)
• Surcharge weight slots: Standard 5 kg disc arrangement
• Frame: Rigid steel, floor-mounted

Applicable Standards

IS 2720 Part 16, ASTM D1883, BS 1377 Part 4, IRC:37.

Accessories Available

CBR mould (150 mm dia), soaking tank, perforated plates, surcharge weights, proving rings — all available separately or as complete test sets.

JS Civil Lab Solutions supplies CBR machines with calibration certificates and post-installation support. Call +91 93596 24761 for pricing and configuration options.