Correlations Between Cone Penetration Resistance and Standard Penetration of some New Zealand Volcanic and Alluvial Deposits

The results of cone and standard penetration tests carried out in Tauranga volcanic soils and in Whangarei alluvial soils are graphically correlated using normal arithmetic plots. The linear least square equation relating the cone tip resistance, qc, and the standard penetration N value is in the form q_c = k * N , where k is a constant. The ratio q_c/N is then used to establish correlations with the type of soil and the results are compared to international findings.

Introduction

CPT-SPT correlations are useful for the conversion of available field test data into the form appropriate for various foundation analyses and design. It is attempted here to prepare correlations on local materials which should lead to better results than others based on internationally collected data. It has frequently been emphasised that it is imperative to rely on locally prepared correlations (eg. Pender, 1998). A new evidence on the significance of deriving correlations on local soils comes from the finding that cone penetration resistance of pumiceous sand is not an indicator of relative density (Wesley et al., 1998). Additionally interesting is the conclusion arrived at by Marks and Larkin (1998) that the low strain shear modulus of the pumice sand is significantly lower than that of quartz sand at similar relative densities and confining pressures. Pranjoto and Larkin (1995) have suggested the grain softness of pumice sand and the high void ratio as being substantially responsible for its different behaviour in comparison to quartz sand. Nonetheless, it is worthwhile mentioning that Takesue et al. (1995) have shown that CPT-SPT correlations as well as pile design values for a volcanic soil distributed in southern Kyushu- Japan and locally known as Shirasu) were consistent with quartz sand values.