Laboratory investigation on the effect of grain size distribution of granular material on penetration test results

Michael Ghali, Mahmoud N. Hussien, Mourad Karray, Mohamed Chekirad, Varvara Roubtsova

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Laboratory and Field Testing

ABSTRACT: This paper initially compares and discusses a majority of correlations between (N1)60 and typical geotechnical parameters such as relative density (Dr), the effective overburden pressure (s'v), void ratio (e), mean grain size (D50), the degree of uniformity (Cu), lateral stress (s'h), mean confinement pressure (s'm), overconsolidation (OCR), aging, and angularity. The paper then presents the results of a series of experimental simulations for standard penetration test (SPT) on both polydisperse spherical glass beads and natural sands samples with different mechanical properties as well as different loading conditions. Stress-strain records along the soil samples are monitored during the tests. Normalized penetration count blows obtained are correlated with typical geotechnical parameters and the corresponding graphs are plotted in order to predict the real behavior of natural soils in the field and to use these graphs to validate numerical simulations based on FEM or DEM. RÉSUMÉ Cet article présente et discute dans un premier temps la majorité des corrélations entre (N1)60 et les paramètres géotechniques classiques tels que la densité relative (Dr), l'état des contraintes (s'v), l'indice des vide (e), la taille de grain moyenne (D50), le degré d'uniformité (Cu), les contraintes latérales, la pression moyenne de confinement (s'm), la préconsolidation, le vieillissement et l'angularité. L'article présente ensuite les résultats d'une série de simulations expérimentales d'essais de de pénétration standard (SPT) sur des échantillons de billes en verre poly-disperses et de sables naturels avec différentes propriétés mécaniques ainsi que différentes conditions de chargement. La contrainte le long des échantillons de sol a été enregistrée au cours des essais. Le nombre de coups normalisés obtenues sont corrélées avec les paramètres géotechniques typiques et les graphiques correspondants sont tracés afin de prédire le comportement réel des sols naturels in-situ et d'utiliser ces graphiques pour valider les simulations numériques basées sur FEM ou DEM. 1 INTRODUCTION Studying the soil parameters affects the standard penetration tests count blows (N) is a unique challenge for geotechnical engineers. Also effects of grain size distributions and mechanical characteristics of sand soils on the SPT count blows (N), are poorly studied, however the engineering experience shows that wide variations in (N) values can occur as between different sands. In fact, part of these variations can be attributed to the use of different test procedures. This part is usually eliminated by normalizing the results to a standard rod energy ratio. The remaining variations are basically due to the nature and the mechanical characteristics of the sands being tested such as; aging, stress history, relative density (Dr), Void ratio (e), mean particle size (D50), coefficient of uniformity (Cu), overburden pressures (s'v), and mean confinement pressure (s'm). This paper presents data of a series of experimental simulations for standard penetration test (SPT) on both polydisperse spherical glass beads and natural sands samples with different mechanical properties as well as different loading conditions. The purpose of the use of the glass beads is the ability to start a parametric study on D50. In fact, parametric study for the above mentioned factors is a very difficult task as most of these factors not only affect N values but also affect each other by somehow. Glass beads allow the elimination of the effects of angularity and stress history under certain Dr, s'v, and coefficient of earth pressure at rest (K0). Also using glass beads allow to verify the results obtained from a DEM software developed by Hydro-Quebec to simulate the SPT. In later stage of this project, few SPT field tests will be carried out in order to verify and test the developed correlations. Procedure and hammering type were fixed in all carried out tests. 2 BACKGROUND INFORMATION Basically changes in test procedures, samplers, hammers and rods lead to corresponding changes in (N) values (e.g. Skempton, 1986). N values widely accepted to be corrected to a standard dynamic energy of 60% of the hammer potential energy (475J) (e.g. Daniel et al., 2003) using the equation: 60*0.60*475ENTHRUNNJ= [1] where ENTHRU is the measured dynamic energy transmitted from the hammer to the drilling rods and N60 being the energy corrected N value.

RÉSUMÉ: atory investigation on the effect of grain size distribution of granular material on penetration test results

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Cite this article:
Michael Ghali; Mahmoud N. Hussien; Mourad Karray; Mohamed Chekirad; Varvara Roubtsova (2014) Laboratory investigation on the effect of grain size distribution of granular material on penetration test results in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper306,author = Michael Ghali; Mahmoud N. Hussien; Mourad Karray; Mohamed Chekirad; Varvara Roubtsova,title = Laboratory investigation on the effect of grain size distribution of granular material on penetration test results ,year = 2014}