Visualization of the formation and features of soil arching within a piled embankment by discrete element method simulation

Abstract

Piled embankments are widely used in highway and railway engineering due to their economy and efficiency in overcoming several issues encountered in constructing embankments over weak soils. Soil arching, caused by the pile-subsoil relative displacement (Δs), plays an important role in reducing the embankment load falling on weak soil, however, the fundamental characteristics (e.g., formation and features) of soil arching remain poorly understood. In this study, a series of discrete element method (DEM) modellings are performed to study the formation and features of soil arching with the variation of Δs in piled embankments with or without geosynthetic reinforcement. Firstly, calibration for the modelling parameters is carried out by comparing the DEM results with the experimental data obtained from the existing literature. Secondly, the analysis of the macroand micro-behaviours is performed in detail. Finally, a parametric study is conducted in an effort to identify the influences of three key factors on soil arching: the friction coefficient of the embankment fill (f), the embankment height (h), and the pile clear spacing (s−a). Numerical results indicate that Δs is a key factor governing the formation and features of soil arching in embankments. To be specific, soil arching gradually evolves from two inclined shear planes at a small Δs to a hemispherical arch at a relatively large Δs. Then, with a continuous increase in Δs, the soil arching height gradually increases and finally approaches a constant value of 0.8(s−a) (i.e., the maximum soil arching height). For a given case, the higher the soil arching height, the greater the degree of soil arching effect. The parametric study shows that the friction coefficient of the embankment fill has a negligible influence on the formation and features of soil arching. However, embankment height is a key factor governing the formation and features of soil arching. In addition, pile clear spacing has a significant effect on the formation of soil arching, but not on its features.

Numerical and theoretical research on stress distribution in the loosening zone of the trapdoor problem

“…About 250 particles are typically contained in a measurement circle. This value is similar to the discrete element models that have been successfully used by Lai et al 14,15 and Jiang et al 43 and can be considered to be large enough to avoid statistical fluctuations. The average stress tensor within a measurement circle in PFC2D is defined by 46…”

“…Substituting Equations 17 and 18 into Equation 15, combining with the boundary conditions of the trapdoor problem…”

“…The objective of this paper is to study the stress redistribution in the loosening zone of a trapdoor problem with confined granular matter by numerical and theoretical analysis. A series of numerical models of trapdoor tests are established through the DEM, which has been widely used in the research of arching effect in granular matter . The stress states in the loosening zone are recorded in the process of the numerical trapdoor test.…”

“…There are also some studies focusing on numerical simulation of the arching effect in trapdoor‐like problems. The soil arching effect in pile‐supported embankments was simulated by Lai et al and Rui et al with the discrete element method (DEM). Pardo et al modelled the trapdoor test through a 2D finite element model with two different constitutive models.…”

“…A series of numerical models of trapdoor tests are established through the DEM, 39,40 which has been widely used in the research of arching effect in granular matter. 8,[14][15][16][41][42][43][44] The stress states in the loosening zone are recorded in the process of the numerical trapdoor test. Changes of the principal stress' direction are calculated, and the shape of major principal stress' trajectory obtained from numerical simulation is compared with other arc, catenary, and parabolic shapes.…”