Discrete element modelling of stress propagation in soil under a rigid wheel in a soil bin։ a simulation of probe inducing stress deviation and wheel speed

Abstract

Discrete element method (DEM) is a suitable technique for simulation of stress propagation in soils, particularly with freshly tilled or aggregated structures. Measurement of true stress, in the absence of a stress-measuring probe inserted in the soil, is not experimentally possible. Stress probes may therefore under- or over-estimate true soil stress. Building on previous work simulating vertical stress propagation under plate sinkage loading, the study modelled stress propagation under a moving rigid wheel. The aim was to determine how vertical stress, with and without a probe, at a given depth may differ under dynamic loading vs. static plate sinkage loading and with varying wheel speed. DEM parameters of the hysteretic spring-linear cohesion contact model were calibrated by a cone penetration test which was validated by wheel sinkage into the soil. Two tests were conducted in a soil bin at a water content of 11% d.b; at a bulk density of 1200 kg m−3 and a wheel loading of 600 N, and at a bulk density of 1350 kg m−3 and wheel loading of 1200 N. Vertical soil stress was measured at 0.15 m depth using a cylindrical load cell probe. The DEM simulation underestimated the measured stress by an average 13%. Average stress overestimation ratio (with/without probe stress) was found to be 1.12, which agreed with measurements beneath the plate during plate sinkage loading. Increasing wheel speed from 0.2 to 6 m s−1 showed a 7% increase in DEM-simulated with-probe stress.