Mechanics Of Granular Matter Research Articles

A theoretical model for evaluating the deterioration of mechanical properties of rockfill materials

The mechanical properties of rockfill materials deteriorate when subjected to different environmental factors. Accurately evaluating the deterioration effect on mechanical properties of rockfill materials is crucial for the lifecycle safety assessment of rockfill dams. In this study, we propose a theoretical model that can analyze the deterioration effect on stress and deformation characteristics of rockfill materials caused by weathering. Specifically, based on assumptions of geometric and breakage similarity, the stress and strain tensors of rockfill assemblies before and after deterioration can be derived from granular matter mechanics by introducing a deterioration coefficient. The deterioration coefficient defines the ratio between the grain crushing strength of deteriorated and undeteriorated rock grains, and can be obtained by single grain crushing tests. The deterioration coefficient is introduced into the Duncan-Chang EB model to quantitatively evaluate the deterioration effect on stress and deformation characteristics of rockfill materials. The triaxial test results of deteriorated and undeteriorated rockfill materials are used to verify the model. The results indicate a good agreement between the model predicted results and experimental results. Besides, the deteriorated stress and deformation characteristics of rockfill materials after cyclic wetting-drying are predicted by the theoretical model.

Identification of stress transfer in asphalt mixtures based on a reconstruction analysis of the simplified coarse aggregate skeleton

Studies on asphalt mixture skeletons have primarily focused on the statistical skeleton morphology while neglecting internal stress transfer. This study therefore proposed a simplified reconstruction-based coarse aggregate skeleton method for analyzing asphalt mixes using the force chain concept from granular matter mechanics. The stress transfer paths and load transfer efficiencies were investigated for three typical aggregate gradations (AC-13, SMA-13, and OGFC-13) and an analysis of their correlation with uniaxial penetration test results was performed. The AC-13 mixture exhibited the largest uniaxial penetration strength (3.30 kN on average) at the lowest failure displacement (4.1 mm on average). As the characteristics of the simplified skeleton were shown to be related to the number of contact points provided between large aggregate particles, the force chain morphology was closely linked to the mixture gradation. The ratio of strong to weak force chains in the AC-13 mixture was approximately 0.77, whereas those of the SMA-13 and OGFC-13 mixtures were significantly different at 0.90 and 1.13, respectively. The transfer efficiencies of the AC-13, SMA-13, and OGFC-13 specimen skeletons considering morphology alone (i.e., under the no-load condition) were 20.94 %, 62.34 %, and 73.57 %, respectively. However, the correlation between the load transfer efficiency of the coarse aggregate skeleton under a specific load and the observed penetration strength reached 0.9. Thus, the simplified skeleton analysis method proposed herein was shown to satisfactorily retain the skeletal characteristics of the mixes.

MECHANICS OF GRANULAR MATERIAL AND THE APPLICATION IN ENGINEERING GEOLOGY

The geological disasters caused by avalanche, large scale deformation, and flow slide of the geo-granular materials have brought massive destruction and potential threats to national economic development and security of lives and property of the people. Most of the geological materials causing those geological disasters can be classified as granular materials. The integration of geological disaster and granular material mechanics is always one of the most important directions for researchers in both soft matter and geological engineering. Granular materials are composited by many individual granules, the mechanical properties of which are extremely complicated. A granular system shows the characteristics of gas, liquid and solid depending on the kinstate of the granules. In the geological engineering field, some typical geological disasters, such as landslides, debris flows, are closely related to the mechanics of granular material. The key to seal with them lies in the phase transition of granular materials or geo-granular materials between solid state and fluid state. This paper first briefly introduced the fundamental characteristics of granular material. The jamming phase transition, local and non-local rheology, and couple typical experimental techniques. It also discussed the application prospect of the mechanics of granular material in geological engineering field. The success of integration of granular material mechanics and engineering geology would expand the research of physics and mechanics of granular matter and provide a theoretical basis for critical engineering and geological disaster prevention.

Structural failure mechanism and strengthening method of fracture plugging zone for lost circulation control in deep naturally fractured reservoirs

Abstract Focused on the lost circulation control in deep naturally fractured reservoirs, the multiscale structure of fracture plugging zone is proposed based on the theory of granular matter mechanics, and the structural failure pattern of plugging zone is developed to reveal the plugging zone failure mechanisms in deep, high temperature, high pressure, and high in-situ stress environment. Based on the fracture plugging zone strength model, key performance parameters are determined for the optimal selection of loss control material (LCM). Laboratory fracture plugging experiments with new LCM are carried out to evaluate the effect of the key performance parameters of LCM on fracture plugging quality. LCM selection strategy for fractured reservoirs is developed. The results show that the force chain formed by LCMs determines the pressure stabilization of macro-scale fracture plugging zone. Friction failure and shear failure are the two major failure patterns of fracture plugging zone. The strength of force chain depends on the performance of micro-scale LCM, and the LCM key performance parameters include particle size distribution, fiber aspect ratio, friction coefficient, compressive strength, soluble ability and high temperature resistance. Results of lab experiments and field test show that lost circulation control quality can be effectively improved with the optimal material selection based on the extracted key performance parameters of LCMs.

Analytical model of corner filling with granular media to investigate the friction effect between tube and media

In a tube forming process, granular matter is used as pressure transmission medium instead of liquid to expand a circular tube into one with square section. In this process, the friction at media/tube interface has a significant effect on the final result. In this paper, an analytical model was developed to determine the influence of the friction on the deformation developing process and final thickness distribution along the tube section. Experimental researches were also implemented to evaluate the analytical model in the end. In this model, four friction situations were applied to the numerical analysis process according to the active or negative function of friction on the flow of metal. The analysis result showed that different friction situations could lead to different deformation processes and thickness distributions. The examination on experiments of AA6061 tube indicated that the experimental data of thickness was extremely close to the analysis result with the friction situation in which the metal flow toward the corner of square section die was impeded by the friction force. However, the analytical prediction of thinning trend of thickness had a deviation compared with the experimental data in the corner region. In addition, the breaking and caking of granules in the tube forming process make the friction situation between the tube and media very complex. Therefore, a further research needs to be conducted from the direction of granular matter mechanics and friction mechanism in order to acquire a more explicit result.

Experimental study on loss-prevention performance of oil-based drilling fluids

Compared to the water-based drilling fluids, lost circulation is more prone to occur when drilling with oil-based drilling fluids and it is difficult to deal with this problem on the drilling site for lack of high-efficiency lost circulation materials. In order to solve this technical problem, the principles of pressure resistance plugging technology of oil-based drilling fluids was firstly investigated according to the force-chain principle of granular matter mechanics, and rigid bridging particles, elastic packing particles and micro fibers could synergistically form fracture tight sealing zones with strong force-chain network to strengthen the lost circulation prevention ability of oil-based drilling fluids. Based on the principle above, novel loss-prevention materials were finally developed for oil-based drilling fluids by optimizing different plugging agents. Experimental results show that novel loss-prevention materials could be compatible with other components of oil-based drilling fluids. The oil-based drilling fluids with high sealing capacity could be optimized by adding novel loss-prevention materials, and it exhibits good rheological behavior with a low PPT filtration of 11.4 mL and excellent lost circulation prevention ability to strengthen the wellbore while drilling.

Interdependence of the Volume and Stress Ensembles and Equipartition in Statistical Mechanics of Granular Systems

We discuss the statistical mechanics of granular matter and derive several significant results. First, we show that, contrary to common belief, the volume and stress ensembles are interdependent, necessitating the use of both. We use the combined ensemble to calculate explicitly expectation values of structural and stress-related quantities for two-dimensional systems. We thence demonstrate that structural properties may depend on the angoricity tensor and that stress-based quantities may depend on the compactivity. This calls into question previous statistical mechanical analyses of static granular systems and related derivations of expectation values. Second, we establish the existence of an intriguing equipartition principle-the total volume is shared equally amongst both structural and stress-related degrees of freedom. Third, we derive an expression for the compactivity that makes it possible to quantify it from macroscopic measurements.

Reflections on the mechanics of granular matter

During recent years, a rather basic conflict has emerged between departments of mechanics/physics concerning the description of granular media. Experts from mechanics measure stress/strain relations, using the so-called triaxial tests, and then use these data to predict the behavior of a sample under given boundary conditions. Some physicists have a different view: they have claimed that it is not possible to define a proper displacement field in a heap of sand, and that the notion of strains is thus ambiguous. In the present text, we conclude that the crucial features are the following: (a) a heap is usually formed from a flowing phase of sand, (b) there is (empirically) a sharp interface between the flowing phase and the frozen heap below, (c) we may define for each grain a displacement, which is measured from the moment when it froze. (This displacement is due, for instance, to a compaction of the heap under its own weight.) We also present some aspects of the dynamics, including dune motions and surface flows of grains. Bouchaud, Cates and coworkers have constructed a very compact description for thin flows. We discuss the practical consequences of this picture, emphasizing some possible extensions for thicker flows. This suggests a number of possible experiments on avalanches.