IIE Lunchtime Seminar - Emmanouil G. Vairaktaris (I.Vardoulakis Laboratory of Geomaterials, NTUA, Greece)

Impact forces of dry granular masses on rigid barriers: comparison of empirical and theoretical approaches with DEM numerical results

Abstract: In the design of sheltering structures as protection measures for very rapid landslide risk mitigation, pseudo-static approaches are very often employed. In this perspective, we present the problem of the assessment of the maximum impact forces transmitted by dry granular (non-cohesive) masses to rigid barriers, using Discrete Element Method (DEM) numerical results. We derive a formula which defines the dependence of the maximum impact force on the Froude number, and a change in the overall behaviour of the soil mass regime (from solid-like to fluid-like) according to a proper measure of the dynamic material stiffness. Several different parameters of the soil-barrier system included in the formula are not yet considered in the existing practice and codes.

The DEM numerical results, are then compared with the data available in the literature, commonly used to assess the value of the maximum impact force transmitted by a sliding dry granular mass to a rigid barrier. The comparison is  hindered by the numerous formulas proposed in the literature, and the numerous field data and experimental data obtained by performing small-scale tests. To simplify the analysis, our numerical data were compared separately with hydrostatic , hydrodynamic and boulder impact approaches.

Our approach is thus employed to (i) discuss the reliability of the existing practice procedures, (ii) highlight the reasons of the scatter among the values obtained by using the approaches proposed in the literature, based on hydrostatic, hydrodynamic and boulder impact theories, (iii) underline that the empirical formulas available in the literature do not take into consideration a series of factors, like, for instance, the front inclination and the void ratio, that in contrast severely affect the maximum impact force value.

Bio: Dr Emmanouil Vairaktaris received initially a diploma in Mathematics from the University of Crete and then the Engineer diploma in Civil Engineering from the National technical University of Athens (NTUA) in 1998. He also received the NTUA MSc in Analysis and Design of Structures (2002) and his PhD in Mechanics at NTUA in 2003 (Supervising Professor: Ioannis Vardoulakis). He has been teaching as a visiting Professor ever since in several Universities in Greece (University of Crete, NTUA, TEI of Piraeus in collaboration with Kingston University) both at undergraduate and postgraduate level. His major research field has been advanced soil mechanics both from theoretical and computational viewpoints. He is presently collaborating with the Politecnico di Milano (Prof. C. di Prisco, Prof. F. Calveti) on the design of stiff landslide mitigation measures (full scale analysis using DEM) and with NTUA (Prof. Y. Dafalias) on the fabric effects in the micromechanical behavior of granular materials and its (fabric) interpretation in constitutive models.