Friction angle and overconsolidation ratio of soft clays from cone penetration test

Abstract

The cone penetration test (CPT) is a method widely used for site characterization as measurements are continuous, fast and economical compared to laboratory testing. However unlike laboratory testing that quantifies soil properties directly, readings obtained from CPT are indirect and needs to be interpreted. Hence many correlations have been proposed to infer a wide range of soil properties from CPT readings. Existing correlations have discovered separate relationships between normalized cone tip resistance (Qt) and effective friction angles (ϕ’), as well as Qt and overconsolidation ratio (OCR). This study employs the press-replace method (PRM), a novel simplified numerical technique, to perform systematic and extensive undrained investigations of CPT in a modified Cam-clay (MCC) soil model. It is the first comprehensive numerical study with an advanced soil model that considers rough cone-soil interactions. The PRM numerical approach overcomes the need to assume the CPT process as analogous to spherical or cylindrical cavity expansions, therefore produces results that are more authentic to real CPT. From the large database of numerical results, an equation is formulated that provides a framework on how Qt is related to both ϕ’ and OCR, rather than separately to ϕ’ or OCR as described in previous correlations. The proposed equation is then simplified so that ϕ’ and OCR can be easily estimated from Qt. Numerical results and predictions from the new equations are then compared to soil behaviour charts, other correlations and field data from different sites.