A Numerical Study of the Effects of Contact Friction on CPT Results

Mohammad Mozaffari, Mason Ghafghazi

In the proceedings of: GeoSt. John's 2019: 72nd Canadian Geotechnical Conference

Session: Numerical Modeling

ABSTRACT: The Cone Penetration Test (CPT) is a popular soil characterization tool as it is fast, cost-effective, and provides continuous measurements. Modelling the cone penetration process has been a common goal for many geotechnical researchers due to the difficulties in developing soil-specific CPT correlations through calibration chamber tests. Modeling the penetration problem encompasses various difficulties including large strains in soil around the advancing probe. Mesh distortions resulting in numerical instability have been the main barrier to developing a full model of the CPT. One of the effective ways that researchers adopt to overcome the mesh distortion is to neglect the contact friction between the penetrometer and soil. However, neglecting friction could result in inaccurate results. To investigate the effect of contact friction, a realistic model of the CPT calibration chamber was created using in the Finite Element software package ABAQUS CAE, and the constitutive model NorSand was implemented in it. The effect of contact friction on CPT tip resistance and sleeve friction was studied for loose and dense sand. The results show that contact friction has a significant effect on CPT results. Therefore, contact friction should be considered in modelling the CPT, and correct contact frictions must be assumed.

RÉSUMÉ: nt, il demeure difficile de développer des corrélations qui soient spécifiques à un matériau à partir des données existantes des chambres de calibration. Plusieurs difficultés se présentent lors de la modélisation du cône tel que les grandes déformations a la distorsion du maillage est de négliger le frottement entre le piézocône et le sol. Cependant, cette approche peut mener à des résultats erronés. Dans la présente étude, un modèle numérique de pénétration du piézocône dans une chambre en pointe (qc) et sur le frottement local du manchon (fs) est étudié pour des sables lâches et denses. Les résultats démontrent que le frottement a un impact majeur sur les données obtenues du CPT. Par conséquent, le frottement entre le cône et le sol ne peut pas être négligé dans un modèle numérique du CPT. surveillée sur le terrain.

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