Evaluation of state parameter interpretation methods using CPT calibration chamber data

The cone penetration test (CPT) is widely used to determine the in situ state parameter of soils because it provides continuous data and excellent repeatability at a relatively low cost. Accurate interpretation of the state parameter from CPT is the basis for evaluating the strength of granular soils, including assessing liquefaction susceptibility in important structures such as tailings storage facilities. A few interpretation methods are used in practice. They use two different overburden stress normalisation schemes on tip resistance. These methods vary in how much information they utilise to differentiate among soils. This paper evaluates these methods by applying them to an extensive database of calibration chamber tests. Then, the state parameter interpreted by each method is compared with that determined from laboratory data. The database includes manufactured sands, natural sands, and clean sand tailings. The soils were selected such that both calibration chamber testing and triaxial compression data were available from the literature. This evaluation serves as a minimum requirement for applying these methods in engineering projects, especially those dealing with challenging soils such as fines-rich tailings. This study suggests that methods that account for soil properties and in situ horizontal stresses perform better than those that do not.