Computational Particle Mechanics https://doi.org/10.1007/s40571-018-00216-x Role of the location and size of soluble particles in the mechanical behavior of collapsible granular soil: a DEM simulation H. Bayesteh 1 · T. Ghasempour 1 Received: 29 July 2018 / Revised: 12 October 2018 / Accepted: 26 November 2018 © OWZ 2018 Abstract Collapsing soil structure caused by mineral dissolution is a challenge to geoenvironmental projects. Although the parameters affecting the macro-response of collapsible soil have been addressed experimentally, the micromechanical behavior of soluble soil is unclear. The aim of this study was to simulate the dissolution behavior of a granular assembly at the particle level. A DEM code was developed that considers both localized and random dissolution as well as the particle size distribution and stress level. The effect of particle dissolution was simulated by considering the role of particle size in the load-bearing skeleton. The results show that mechanical behavior of a granular assembly is strongly influenced by the location and percentage of dissolution of particles. The loss of the soluble particles decreases physical contact and transfers to neighboring particles due to the arching forces around the voids, as in a honeycomb structure. However, if the soluble areas cut across the load-bearing force chains, a honeycomb fabric cannot form because of the lack of an arching effect, leading to the collapse of the structure and large volume change. Particle loss of up to 3% will not have a serious impact on the mechanical behavior of the granular assembly. After fine particle dissolution of a binary mixture, the arching effect around them decreases the volumetric strain in comparison with the dissolution of coarse particles. Also, during dissolution, the high stress level will decrease the peak friction angle, but the opposite is true for the post-dissolution behavior above 12% strain. Keywords DEM · Dissolution · Collapsible soil · Force chain · Particle size 1 Introduction Collapsible soil is a problematic soil that can be found in diverse areas with high geotechnical problems [1]. The primary drawback to the description of its properties is assessment of the degradation of mechanical characteristics due to the presence of water or by particle dissolution [2]. Collapsible soil is unsaturated porous media usually consist- ing of poorly graded soil with soluble parts that has high porosity. An increase in the void ratio due to the dissolu- tion of minerals such as carbonates, calcite, dolomite and gypsum [3] causes loss of contact between the soil particles as well as sudden collapse of the soil media structure and large deformation [4–6], especially sinkholes, in the case of localized dissolution [7]. Changes in the environmental con- ditions, water table, stress level [8], particle dissolution due B H. Bayesteh h.bayesteh@qom.ac.ir 1 Department of Civil Engineering, University of Qom, Qom, Iran to climate change such as acid rain [9] and human activity, which changes the natural equilibrium, such as in the pH of the soil–water system [10], can cause settlement in collapsi- ble soil [11]. The volume change in collapsible soil depends on the pore size distribution and the interaction between soluble particles in the honeycomb-like soil formation [12, 13]. Experimental studies have reported on the influence of parti- cle dissolution on the compressibility of collapsible soil from the physico-chemical perspective [14–17] as well as on the need for better understanding of the mechanical influence [2, 6, 18]. In pore fluid chemistry, studies have shown that the carbonate content, stress state and particle cementation during particle dissolution increase the void ratio [18] and decrease the lateral soil pressure ratio (k 0 )[19], shear wave velocity [6, 20], friction angle [21] and cone penetration resistance [22] and increase permeability [20]. Mcdougall et al. [23] experimentally showed that both size and the per- centage of soluble particles affect the void ratio and change the overall volume. In these studies, laboratory tests such as oedometer tests, were commonly used to model the one- 123