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The purpose of this paper is to present an investigation of the effect of different gravity conditions on the penetration mechanism using the two-dimensional Distinct Element Method (DEM), which ranges from high gravity used in centrifuge model tests to low gravity incurred by serial parabolic flight, with the aim of efficiently analyzing cone penetration tests on the lunar surface.

Seven penetration tests were numerically simulated on loose granular ground under different gravity conditions, i.e. one-sixth, one-half, one, five, ten, 15 and 20 terrestrial gravities. The effect of gravity on the mechanisms is examined with aspect to the tip resistance, deformation pattern, displacement paths, stress fields, stress paths, strain and rotation paths, and velocity fields during the penetration process.

First, under both low and high gravities, the penetration leads to high gradients of the value and direction of stresses in addition to high gradients in the velocity field near the penetrometer. In addition, the soil near the penetrometer undergoes large rotations of the principal stresses. Second, high gravity leads to a larger rotation of principal stresses and more downward particle motions than low gravity. Third, the tip resistance increases with penetration depth and gravity. Both the maximum (steady) normalized cone tip resistance and the maximum normalized mean (deviatoric) stress can be uniquely expressed by a linear equation in terms of the reciprocal of gravity.

This study investigates the effect of different gravity conditions on penetration mechanisms by using DEM.

Shear-induced strain localization in granular materials has been a hot topic under intensive research during the last four decades. However, the micromechanical process and mechanisms underlying the initiation and development of shear bands are still not fully understood. The purpose of this paper is to eliminate this deficiency.

The paper carries out several two-dimensional distinct element method simulations to examine various global and local micromechanical quantities particular the energy dissipation and local stress and strain invariants with a special emphasis on the initiation and propagation of shear bands. Moreover, the effects of various influential variables including initial void ratio, confining stress, inter-particle friction coefficient, rolling resistance coefficient, specimen slenderness and strain rate on the pattern, scope and degree of shear bands are investigated.

Novel findings of the relationship between sliding and rolling dissipation band and shear band are achieved, indicating a plastic dissipation nature for the shear band. The high inter-particle sliding or rolling resistance, relative small initial void ratio, relative low confining stress and high strain rate facilitate the formation of shear band. In addition, the specimen slenderness affects the pattern of shear band.

In this paper, a comprehensive and deep investigation on shear band formation linked with localization of energy dissipation and strain invariants was presented. The new findings on particle scale during shear band formation helps to develop robust micromechanics-based constitutive models in the future.

Retained excavation is important for future lunar exploratory missions and potential human colonization that requires the construction of permanent outposts. Knowledge in excavation obtained on the Earth is not directly applicable to lunar excavation because of the low lunar gravity and the non-negligible adhesive van der Waals interactions between lunar regolith grains. This study aims at revealing how the gravity level and lunar environment conditions should be considered to extend the knowledge in Earth excavation response to lunar excavation.

Two-dimensional Discrete Element Method (DEM) simulations were carried out to investigate the respective effect of gravity level and lunar environment conditions (high vacuum and extreme temperature) on retained excavation response. A novel contact model was employed with a moment – relative rotation law to account for the angularity of lunar soil particles, and a normal attractive force to account for the van der Waals interactions.

The simulation results showed that the excavation response is non-linearly related to the gravity level. Van der Waals interactions can increase the dilatancy of lunar regolith and, surprisingly as a consequence, significantly increase the bending moment and deflection of the retaining wall, and the ground displacements. Based on the simulation results, a parabola model was proposed to predict the excavation induced lateral ground movements on the Moon.

This study indicates that an unsafe estimate of the wall response to an excavation on the Moon would be obtained if only the effect of gravity is considered while the effect of van der Waals interactions is neglected.

Wonders whether, owing to severely restricted access, China’s government policy towards digital communications will remain in a constant state of flux – or will it gain economic benefits without a social penalty? Concludes that China has to link the forces of change to channel and deflect domestic resistance.

The study aims to investigate the effects of pre-loading histories (pre-shearing and pre-consolidation) on the liquefaction behaviour of saturated loose sand via discrete element method (DEM) simulations.

The pre-shearing history is mimicked under drained conditions (triaxial compression) with different pre-shearing strain levels ranging from 0% to 2%. The pre-consolidation history is mimicked by increasing the isotropic compression to different levels ranging from 100 kPa to 300 kPa. The macroscopic and microscopic behaviours are analysed and compared.

Temporary liquefaction, or quasi-steady state (QSS), is observed in most samples. A higher pre-shearing or pre-consolidation level can provide higher liquefaction resistance. The ultimate state line is found to be unique and independent of the pre-loading histories in stress space. The Lade instability line prematurely predicts the onset of liquefaction for all samples, both with and without pre-loading histories. The redundancy index is an effective microscopic indicator to monitor liquefaction, and the onset of the liquefaction corresponds to the phase transition state where the value of redundancy index is one, which is true for all cases irrespective of the proportions of sliding contacts.

The liquefaction behaviour of granular materials still remains elusive, especially concerning the effects of pre-loading histories on soils. Furthermore, the investigation of the effects of pre-consolidation histories on undrained behaviour and its comparison to pre-sheared samples is rarely reported in the DEM literature.

The purpose of this paper is to explore the variation law between the clay microstructure and macro external force by using soil scanning electron microscope (SEM) images.

First, SEM images of clay were pre-processed by MATLAB, and quantitative statistical parameters such as directional probability entropy, fractal dimension and shape factor are extracted. Second, the distribution force model was proposed, considering that the microscopic parameters of soil particles were independent of each other, and the distribution coefficient was determined according to the analytic hierarchy process (AHP). Then, the fitted formula of quantitative statistical parameters based on the distribution force model was obtained by taking the macroscopic distribution force as independent variable and the microscopic parameters of soil particles as dependent variable. Finally, the correctness of corresponding fitting formula was verified.

The results showed that the change of external consolidation pressure has great influence on the directional probability entropy and fractal dimension, while the shape factor reflecting the regular degree of soil particle shape is less sensitive to the consolidation pressure. The fitting formula has high accuracy, and mostly the R value can reach more than 0.9. All the data have passed the test, which proves that the distribution force model proposed in this paper is rational.

The model can be used to connect the macroscopic stress of soil with the micro-structure deformation of soil particles through mathematical formula, which can provide reference for engineering practice.