CPT calibration

The CPT is often used empirically as in the NCEER method, but can do much more. If thoroughly analysed, the CPT is capable of determining the state parameter to a precision of about 0.03. The matching precision in void ratio is less accurate because the CPT responds to the soil s state parameter, not its void ratio, and calculating void ratio from the state parameters need the CSL—a further set of data with its own uncertainty caused by natural variation in fines content. 

Thorough analysis of the CPT is based on calibration in a large cell, involving as much as 2 tonnes of sand for a single calibration point. Such calibrations have been carried out mainly for research sands, but also including some sands used in large scale hydraulic fill projects. The challenge these calibration data present is that there is not a unique relationship between tip resistance, void ratio and 

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