In Situ CBR’s
In situ California Bearing Ratio (CBR) tests are carried out to assist in the design of new roads and carriageways. A plunger is wound at a uniform rate of 1mm per min to a maximum depth of 7.5mm, and the resistance the soil gives recorded as force versus penetration. The test results are plotted and the CBR values taken at 2.5mm and 5.0mm penetration. This test is really only suitable for material of less than 20mm in diameter. For material greater than 20mm either plate bearing or DCP tests should be considered.
The In situ Dynamic Cone Penetration ( DCP) test comprises the measurement of an 8kg weight falling through 575mm on to an anvil, which drives a 60 degree cone through the material tested, and the resistance of the soil measured. The number of blows and the penetration depth are recorded.
Rapid in-situ measurement of structural properties
The TRL (Transport Research Laboratory) Dynamic Cone Penetrometer is lightweight instrument designed for the rapid in-situ measurement of the structural properties of existing road pavements and subgrade strata. Continuous measurements are made to a depth of around 900mm and these are then converted to CBR values. The strengths and boundaries of the soil layers can be identified and the layer thicknesses determined.