CPTu-DMT Stress-Path Fusion for Clay Friction-Angle Estimation Under Overconsolidation

Abstract

The accurate determination of the effective friction angle in overconsolidated clay remains a formidable challenge in geotechnical engineering due to the complex stress-strain behavior and the limitations of isolated in-situ testing methods. Traditional laboratory methods suffer from unavoidable sample disturbance, leading to unrepresentative shear strength parameters, while single-source in-situ methods like the Piezocone Penetration Test and the Flat Dilatometer Test often fail to capture the complete stress-path evolution during penetration and expansion. This paper proposes a novel framework for estimating the effective friction angle of overconsolidated clays by fusing the stress-path responses derived from both the Piezocone Penetration Test and the Flat Dilatometer Test. By leveraging the continuous continuous profiling capability of the piezocone and the horizontal stress sensitivity of the dilatometer, the proposed methodology reconstructs the localized stress history and the multidirectional strain fields around the advancing probes. The analytical model rigorously incorporates the Overconsolidation Ratio as a foundational variable that moderates the relationship between the horizontal stress index and the normalized cone resistance. The framework is validated against a comprehensive set of consolidated undrained triaxial laboratory tests recovered from diverse geological sites. Results demonstrate a significant reduction in predictive uncertainty, minimizing systematic errors that traditionally plague empirical correlations. The fused model provides a theoretically sound, practically robust, and computationally efficient approach for the in-situ characterization of heavily overconsolidated deposits, fundamentally enhancing the reliability of subsequent geotechnical design processes for deep foundations and earth retaining structures.