Paper No. ETEBA EXPLORING THE EFFECTS OF STRESS HISTORY ON THE DRAINED AND UNDRAINED CYCLIC BEHAVIOUR OF GRANULAR MATERIALS Daniel BARRETO 1 ABSTRACT This paper presents the results of 3D DEM simulations of granular materials subject to cyclic loading. While both the drained and undrained conditions are considered, the effects of depositional history and consolidation stress history on the stress-strain response are specifically evaluated. It is demonstrated that the different stress histories have a significant effect on soil response and that such effects can be attributed to differences in the initial particle arrangement (fabric). Keywords: cyclic loading, stress history, DEM, undrained, drained INTRODUCTION It is widely recognised amongst geotechnical engineers that the laboratory response of granular materials is dependent on the sample preparation method (e.g. Oda, 1972; Miura & Toki, 1982; Vaid & Negussey, 1988). These different methods to prepare samples in the laboratory intend to replicate the mode of particle deposition in the field. The literature available has demonstrated that different deposition methods generate different particle arrangements (fabrics) which account for the subsequent behaviour of soils when subject to external loads. An ideal technique to analyse the influence of fabric is the Distinct Element Method (DEM). It allows simulating granular materials accounting for their particulate nature. Hence, particle arrangement, inter- particle contact orientations as well as other micro-mechanical quantities can be easily monitored. Furthermore, in contrast to physical experiments, the same numerical sample can be used to model different deposition and stress histories. Previous DEM research has shown that the macro-scale behaviour of granular materials is the result of an evolving internal micro-structure (fabric) and the transmission of stresses via inter-particle contacts generating complex networks of contact forces. These features can and have been previously quantified (i.e. Thornton, 2000; O‟Sullivan et al, 2008). Furthermore, Yimsiri & Soga (2010) have studied the effect of different initial fabrics on the monotonic response of granular assemblies. Note however, that the previous studies have considered either a limited number of cycles when studying cyclic loading, or have compared the undrained and drained response for monotonic loading only. The present study summarises the results of three-dimensional DEM simulations on numerical specimens when subject to cyclic loading under drained and undrained conditions for 100 cycles, which were sufficient to produce failure in one of the specimens. Two different specimen preparation methods were used in order to obtain different initial fabrics using an approach similar to that proposed by Yimsiri & 1 Lecturer, School of Engineering and the Built Environment, Edinburgh Napier University, e-mail: d.barreto@napier.ac.uk