Full State of Stress and Strain at a Point near the Cone during Penetration Tests in Sand

Abstract

Cone penetration testing (CPT) in calibration chambers is used to develop empirical correlations and validate numerical models. Hundreds of tests have been performed over the last few decades on sands, but nearly all reported only standard CPT data. Understanding the cone penetration process is ultimately about quantifying what the soil feels as the cone approaches and passes through a horizon. This will enable connecting CPT measurements to soil conditions around the cone and improving interpretation methods. With the progress in numerical modeling of the CPT and the need for better validation, there is a need for better understanding the penetration process and quantifying the changes in stresses and strains induced in soil during penetration. This paper presents CPT calibration chamber tests on a sand, with local stress and strain measurements adjacent to the cone and at the chamber boundary. A strong correlation between CPT tip resistance and the state parameter was found. Utilizing novel sensing equipment enabled the characterization of the full state of stress and strain at a point in the sand mass during penetration. The stress path, stress–strain relation, and rotation of the principal stresses as the cone approached and passed the measurement point are discussed. This work offers a new way of validating numerical models of deep penetration in soil, which are becoming more realistic with the advent of material point and particle finite-element methods and advances in arbitrary Lagrangian Eulerian finite-element methods.