Indirect measurement of relative density by SPT testing

Several correlations between the Standard Penetration Test (SPT) value and the relative density exist. One of the most commonly used correlations is the Gibbs and Holz correlation. 

It should be noted that the British Standard classification of the relative density of a sand or gravel is based on the SPT value, see Table 8.4. This means that some correlation has been adopted already. 

5 Measurement of in situ state parameter i/hy cone penetration testing 

In critical state soil mechanics, the state parameter used to express the difference between void ratio and void ratio at critical state, for the same effective stress. This concept is used, among others, in hquefaction analysis and reference can be made to Section 8.6.2 for a basic explanation of this parameter. 

State parameter y/, the preferred measure of in situ state within a critical state framework, can be measured (interpreted) from cone penetration tests with reasonable precision. Without measuring the critical state properties of the sand (e.g. M, A), shear modulus G or plastic hardening, interpretation relies on the friction ratio and parameters as indicators of material type and a precision in of 0.08 is possible. With supporting laboratory testing to determine the critical state parameters and measurement of with a seismic CPT, a precision in Xffof 0.02 can be achieved. Plewes et al. (1992), Been and Jefferies (1992) and 

---