The use of the in-situ CBR apparatus in large road construction projects has increased considerably in the recent years. This apparatus, mounted on a rolled steel joist cantilevered from the back of the truck or fitted to the underside of a mobile frame, can be used to determine the bearing ratio (generally known as the California Bearing ratio) of soils quickly and efficiently for the evaluation of strengths of sub-grade & bases for roads & runway pavements. This method of testing in-situ, using piston penetration, is useful for determining the load carrying capacity in the field, when the in-place density and water contents are such that the degree of saturation is 80% or greater, when the material is coarse grained and cohesion less so that it is not affected by changes in the water content when the material has been in-place.
Ref. Standard IS:2720 (Part 31)