A particle refinement method for simulating DEM of cone penetration testing in granular materials

Abstract

Discrete-element modelling of cone penetration testing (CPT) of granular materials in a calibration chamber has been performed. It was established that simulating the entire chamber with a realistic particle size requires too many particles. Simulating a segment of the chamber partly solves the problem, but the number of particle contacts at the cone tip is unrealistically small. A particle refinement method was therefore developed whereby particles nearer the cone tip were smaller than those further away. This was found to give a pronounced effect on the ability to model CPT in soils using the discrete-element method.

Discrete element modelling and cavity expansion analysis of cone penetration testing

“…The experimental results of Schnaid [16] for Leighton Buzzard sand was used as a benchmark for comparison with the numerical model and to establish the suitability of the model parameters. In order to obtain a larger number of small particles in contact with the cone tip, the authors' subsequently used a 'particle refinement method' [12], whereby small particles were generated close to the cone penetrometer, and larger particles further away. They simulated sand particles of size 1.5 mm near the cone penetrometer, using both 90° and 30° segments of the calibration chamber.…”

“…As such, the model used in this study comprises a refined sample of spheres simulated in a 30° segment of a calibration chamber, shown in Figure 1. The samples used consist of a minimum of three zones of different-sized particles; the difference in particle size between any neighbouring zones is chosen so as to prevent excessive migration of the smaller particles into the larger voids [12]. The numerical chamber comprises five finite frictionless walls that serve as sample boundaries to confine the particles during sample generation and equilibrium (outer cylindrical wall, two vertical planar walls at 30° to each other, top and bottom planar walls).…”

“…In this paper a particle refinement method [12] is implemented to simulate CPT in a 30° segment of a calibration chamber. In order to improve the computational efficiency of the simulations, the radius expansion method is used to generate the sample, and constant particle mass (i.e.…”

Steady state of solid-grain interfaces during simulated CPT

“…Arroyo et al [1] validated this approach, showing that 3D DEM models of CPT in a calibration chamber resulted in cone point resistance values in close agreement with predictions based in physical models. Several aspects of this type of models have been explored further by Butlanska et al [3], Butlanska et al [4], McDowell et al [11], Lin and Wu [8] and Arroyo et al [2].…”

Editorial: Geomechanics across the scales

“…The computational model acknowledges the limitation of discrete-element methods (DEM) in handling full-scale problems and thus it is used as a constitutive input for the Gauss points of the finite-element method (FEM). In the next paper, McDowell et al (2012) present a method that aims to reduce this DEM limitation in an alternative way, by developing a particle refinement method. The method is applied to simulate cone penetration while maintaining the original particle size in the vicinity of the tip of the cone penetrometer; that is, small and realistic in the zone deemed to be important while particles further away, where the particle size is deemed to be less important, are larger.…”