In-Situ California Bearing Ratio (CBR) test

In-Situ California Bearing Ratio (CBR)
The In-Situ California Bearing Ratio (CBR) test is a commonly recognized field procedure used to determine the strength of subgrade soil, subbase, and base course materials under direct loading. It assesses the bearing capacity of various materials by measuring the resistance to a standard plunger, providing valuable information for pavement and road design. The test is especially relevant for in-situ circumstances, because laboratory CBR results may not accurately reflect the natural variability of the field environment. The in-situ CBR test, carried out in accordance with BS 1377-9 and ASTM D4429, is useful in guiding thickness design for flexible pavements and overlays, especially in highway, airport, and rail construction. By documenting site-specific soil behavior under stress, the test enables engineers to evaluate uniformity, identify weak zones, and make educated design or remediation decisions.

Advantages of in-situ CBR:

• Real-time evaluation of subgrade strength.
• There is no requirement for sample extraction or laboratory testing.
• Reduces delays in building planning.
• Validating road and airfield designs is essential.
• Matches industry requirements for field evaluation.