DEM Analysis Research Articles

DEM analysis on the stress wave response of spherical particle assemblies under triaxial compression

It is challenging to understand the stress wave response of cohesionless particle assemblies including compression and shear wave velocities (Vp and Vs) due to complicated particle-scale interactions particularly during a loading process. This contribution adopts the discrete element method to simulate triaxial compression experiments using spherical particles. Four samples are isotropically confined at various initial packing densities and then sheared monotonically up to the critical state. Small-amplitude wave propagation simulation is performed during shearing along the axis of loading. The results reveal that Vp is affected by the major principal stress and the coordination number contributing to the vertical direction rather than horizontal direction, while Vs is more influenced by the geometric mean stress and the mean coordination number. The wave velocity ratio (Vp/Vs) is well correlated with the fabric anisotropy, having a linear relationship. This enables prediction of microscopic change in fabric from macroscopic wave velocity values. Besides, a material-specific relationship between stress levels and wave velocities is found at the critical state with a unique fabric anisotropy, independent of initial packing. Vs in the isotropic state is found to be always larger that at the critical state under an equivalent stress level.

Numerical DEM Analysis on Coal Loading Process of Shearer Spiral Drum

Background: In order to study the loading process of shearer spiral drum, the theoretical model of loading process of spiral drum was established based on the kinematic characteristics of coal block in the envelope region of spiral drum. Objective: A spiral drum was designed for MG400/951-WD shearer, and this spiral drum was taken as the research object, the influence of spiral angle of the blade and rotation speed of the spiral drum on the theoretical coal capacity was analyzed. Methods: The intrinsic parameters of coal were calibrated according to the physical and mechanical properties of coal samples in Ordos Wenyu coal mine, a discrete element model of the coupling of the spiral drum and the coal wall was constructed. Results: The velocity and mass distribution of coal particles in the loading process were obtained by numerical simulation. The simulation results show that the loading rate of spiral drum was 65.6%. Through industrial test and theoretical calculation, the coal loading rate of spiral drum under the same conditions was 63% and 68.4%, and the maximum relative error between the results and theoretical calculation was 7.89%. Conclusion: The error between the coal loading rate obtained by the simulation, theoretical calculation and the test was small. It shows that the simulation results can accurately reflect the coal charging process of the spiral drum. In this article, various patents have discussed.

DEM Analysis and Evaluation of Hopping Motion on a Sandy Surface in Microgravity

DEM Analysis and Evaluation of Hopping Motion on a Sandy Surface in Microgravity

DEM analyses of cemented hydrate’s effect on the compression behavior of fine-grained sediments

The participation of gas hydrate constitutionally affects the mechanical properties of gas hydrate-bearing sediments. The hydrates contribute to the mechanical properties of hydrate-bearing sediments by pore-filling, bearing and bonding effects. A discrete element model of hydrate-bearing silt was established randomly filled by the hydrate particles into silt-sized granular skeleton reservoir. The cluster & bonding hydrate is generated in the pores of the numerical silt reservoir to study hydrate’s mechanical effects. One-dimensional loading was applied to the numerical sample to investigate its volume change, bond degradation and stress transmission. The main conclusions are as follows. The structural yield stress corresponds with the abrupt bond breakage. Particles and contacts will be redistributed after the widespread bond breakage. The breakage of hydrate-hydrate bonded contacts is more quickly than that of silt-hydrate contacts ascribe to a crushing process of hydrate clusters (especially for SMH=45%).

4-② 地震前後の衛星SAR画像解析とレーザ地形データ差分解析による造成地周辺の地盤変位

4-② 地震前後の衛星SAR画像解析とレーザ地形データ差分解析による造成地周辺の地盤変位

DEM analysis of the plugging effect of open-ended pile during the installation process

Mechanisms governing the sand plug behavior inside an open-ended pile are examined using the discrete element method. A series of numerical pile penetration tests have been conducted by considering the influence of soil density, pile geometry and installation method. A novel sample generation method, based on the replication of unit cell, is applied to produce a large and homogeneous sample efficiently. According to the soil deformation pattern, a “nose cone”, with the length about one pile diameter, has been observed beneath the small diameter jacked pile at the end of penetration. Plugging effect is shown to be more prevalent for jacked piles than dynamic installed piles. Also, larger penetration, smaller diameter and higher soil density all seem to promote plug formation, while the influence of wall thickness is not that obvious. This conclusion is later verified by the development of Incremental Filling Ratio (IFR) and porosity distribution. Furthermore, remarkable stress concentration has been observed at the lower part of the soil plug. The development of installation resistance indicates that jacking produces the largest resistance while dynamic installation methods ease pile penetration. Further analysis based on particle movements, contact force chain distribution and stress orientation provides a micromechanical perspective of the plug behavior. Finally, the plug resistance mobilization process at different plugging conditions and the formation process for soil plug are illustrated.

GRASS GIS Modules for Topographic and Geophysical Analysis of the ETOPO1 DEM and Raster Data: North Fiji Basin, Pacific Ocean

The paper presents topographic analysis based on the raster data (NetCDF and grid formats) and visualization of the geophysical datasets that resembles the topographic surface. Geographically, the research focuses on the region of North Fiji Basin, South Pacific Ocean. North Fiji Basin is one of the marginal basins located at the converging boundary between the Pacific and Australian tectonic plates and is notable for complex geological settings. Methodology is based on GRASS GIS and includes scripting and cartographic visualization. Data include ETOPO1, GEBCO, EGM96 gravity and geoid raster grids imported to GRASS GIS via GDAL library (‘r.in.gdal’ module) from NetCDF and GRD formats, evaluated and visualized. Several GRASS modules were used as a sequential scripting for displaying and modelling data. Geomorphometric analysis (slopes, curvature, aspect, elevation) was performed by module ‘r.slope.aspect’ based on ETOPO1 grid. Statistical data analysis (histograms, polar diagram) for topographic and geoid gravitational fields were visualized by combination of GRASS modules d.rast, g.region, d.polar, d.histogram, d.grid, d.legend, d.text. Topographic analysis reveal that free-air gravity anomaly mark the continental shelf-slope border showing that generally, geophysical settings are dominated by the topographic effect. These observations are consistent with the inferred prominent role of the geophysical settings. The histograms reveal that topography (trenches, abyssal plains, shelf areas) has values between -5,000 and -1,000 m, and a clear peak with major values between 100 and 350 m above sea level. This distribution indicates that dominating depths of the ocean floor in North Fiji Basin are between -1,500 to -3,000 m. The aspect map of the ETOPO1 initial raw raster grid show that the surface has mostly 50°-110° oriented slope followed by data range in 250°-300° oriented slopes which is well correlating with submarine topography and general relief forms. The steepening of the gravity values between 50 and 55 mGal and 58 to 63 mGal indicates geoid undulations suggesting that bathymetry is controlled by the geological settings in the study area. Console- based scripts of GRASS GIS are presented together with cartographic outputs showing its effectiveness for the geographic spatial analysis.

A first approach towards DEM analysis of plasticity in pebble beds

• A first approach towards quantifying plastic deformation inside DEM code was implemented. • The in-house KIT DEM code was extended by implementing the Thornton theory. • Good agreement between experiments and numerical results in terms of maximum stress and residual strain. • The approximation introduced by the theory results in some differences during the evolution of the mechanical behavior. • Finite Element analyses were carried out to investigate and adjust discrepancies. In the solid blanket concept, the tritium breeder and the neutron multiplier are both used in the form of pebble beds. Due to their discrete nature, the Discrete Element Analysis (DEM) allows determining the macroscopic behaviour of the bed as a result of the microscopic interactions among pebbles. At the Karlsruhe Institute of Technology, a Discrete Element Code (KIT DEM code) is constantly under development to support the R&D on the solid breeding blanket. As a further extension of the code, a first approach towards implementing plastic deformation inside pebble beds was investigated. By simulating the plastic deformation of each single pebble, the macroscopic plastic strain of the bed is defined jointly with the rearrangement of the particles in the assembly. Among the approaches reported in literature, the Thornton theory was selected and implemented. In order to validate the method, a comparison with experiments already reported in literature was carried out. Numerical results are in good agreement with the experiment in terms of maximum stress and residual strain. However, due to the approximation introduced by the theory, a perfect linear behaviour which differs from the experimental results is obtained during the plastic loading phase. In this sense, Finite Element analyses were carried out to adjust the correlation describing the plastic loading occurring during uniaxial compression.

New Macroseismic and Morphotectonic Constraints to Infer a Fault Model for the 9 (Mw6.1) and 11 January (Mw7.3) 1693 Earthquakes (Southeastern Sicily)

This study deals with the earthquakes which occurred in southeastern Sicily in 1693 (January 9 and 11, Mw ≈ 6.1 and 7.3, respectively). Although they have been largely studied, robust and commonly accepted seismic sources are still missing. We performed a revision of the 1693 macroseismic data and, for the fore and main-shocks, modeled new NNE-SSW trending seismic sources. In the Hyblean Plateau area, we carried out an analysis of DEM and aerial photos to map tectonic features. Then, we performed field surveys on the main faults, and a morphotectonic study with the aim of characterizing the activity of mapped faults. The study revealed the presence of three main fault systems. The first is the Palazzolo-Villasmundo Fault System, composed of NNE-SSW and NE-SW trending north-west-dipping normal faults. Some of these faults could be reactivated as reverse faults. The second is the Augusta-Floridia Fault System, made of NNW-SSE and NW-SE normal faults. The third is composed of faults which have never been mapped before: the Canicattini-Villasmundo Fault System that shows both a segmented and stepping pattern, almost N-S trending and west-dipping normal faults; some of these faults show a left-lateral movement. The morphotectonic study demonstrated that the fault systems are active. Furthermore, both strike and kinematics of the studied faults well match with the regional stress field characterized by a NW-SE σ1, which in the study area is probably both affecting some pre-existing faults, the Palazzolo-Villasmundo and the Augusta-Floridia Fault Systems, and causing the formation of new faults, the Canicattini-Villasmundo Fault System. The latter system lies across the Hyblean Plateau with a total length of 35 km and, due to its aligned segmented pattern, it can be the surface expression of a master fault that seems dividing the Hyblean Plateau in two blocks. Moreover, the Canicattini-Villasmundo Fault System well fits the southern part of the 1693 revaluated seismic sources and matches with a current alignment of shocks mainly characterized by left-lateral focal mechanisms on almost N-S fault planes. Considering the possible rupture length in depth, it could manage to release Mw ≈ 7.1 earthquakes, representing a valuable candidate source for the 1693 earthquakes.

DEM and theoretical analyses of the face stability of shallow shield cross-river tunnels in silty fine sand

A discrete element numerical simulation is used to evaluate the face stability of a shallow shield cross-river tunnel through silty fine sand. The micro mechanism of silty fine sand is first studied with direct shear tests and the micro parameters are calibrated. A shallow shield cross-river tunnel model is then conducted considering the water pressure and buoyancy force. Failure mechanism of the soil in front of the tunnel face is analyzed by measuring the characteristics of shear strain, sliding fraction, volumetric strain, particle displacement, and the cohesive failure zone. The results show that a wedge model in front of the tunnel face is first formed and as the displacement of the piston movement increases, the area of the failure zone in front of the tunnel face is enlarged. Base on the numerical results, a new analytical model for shallow shield cross-river tunnels in silty fine sand is proposed. The theoretical solution of limit support pressure of the proposed model is deduced. The normalized support pressures calculated by the present model are in good agreement with other existing well-established methods that the proposed model can be availably applied to the shallow and deep cross-river tunnels.

A DEM analysis of geomembrane-lined landfill subject to vertical loading

Particle flow code in three dimensions (PFC3D) is used to investigate the bearing capacity and mechanism of a geomembrane-lined landfill under construction loading. The soils and the geomembranes are simulated by numerous balls and parallel bond, respectively. The initial states and loading processes of geomembrane-lined soil are simulated by PFC3D method. The displacement vector diagram, the velocity vector diagram, the stress and the porosity of soil were analyzed using the numerical models. The simulation results demonstrate that the geomembranes keep the underneath soil particles from being displaced under the applied load and can distribute the load uniformly over a wider area. The interface between soil particles and geomembranes, the displacement vector, the contact force and the deformation of the geomembranes are also analyzed. The results showed that the vertical loading affect strength-strain behavior of geomembranes. The contribution of radial displacements on strain and, consequently, the stress crack and potential failure mechanism of geomembranes were analyzed.

3D FEM and DEM Analyses of Underground Openings in Competent Rock Masses

The paper is aimed at comparing the results of numerical analyses of underground openings in competent rock masses like the Carrara Marble (Italy) by considering a real and well documented case study. More specifically, 3D FEM and DEM analyses were carried out on a rock-mass model interested by two faults and three sets of discontinuities. The geometrical model is representative of deep underground openings where spalling-cracks and rock bursts can occur. PLAXIS 3D and 3DEC were used for the analyses. Intact rock and rock mass characterization of Carrara Marble was inferred from available technical literature. The analysis results were compared in terms of principal stresses and displacements in a number of monitoring points around the opening. The main practical interest is to find out a reliable approach for evaluating the stability of very large openings in a competent rock mass like Carrara marble. For such a purpose, a number of available in-situ stress measurements were used.

Geomorphology of the high-elevated flysch range – Mt. Babia Góra Massif (Western Carpathians)

ABSTRACT A detailed geomorphological map of the Mt. Babia Góra Massif (1725 m a.s.l.), at a scale 1:10,000 is presented. A slope, glacial, periglacial and fluvial features were mapped on the base of the coupled field studies and LiDAR DEM analyses. This study underlines the complexity of rock slope failures (RSFs), in shaping the morphology of compact and isolated upland, exhibiting one of the highest incidences of RSFs yet recorded in Europe (29% for a whole massif, and 45% for the north face). A total of 212 RSFs were mapped of which 18 failures are large landslides (>0.25 km2), among them is one of the largest known (2.6 km2 and 150 × 106 m3) in the Polish Flysch Carpathians. The mapping and Schmidt-hammer results shed light on the problem of glacial relief of the massif, documenting the remnants of glacial deposits beyond the tongues of landslides in the Szumiąca Woda valley.

Area and Mass Changes of Glaciers in the West Kunlun Mountains Based on the Analysis of Multi-Temporal Remote Sensing Images and DEMs from 1970 to 2018

Most of the world’s glaciers have retreated significantly against the background of recent climate warming, while reports have indicated that the glaciers in the West Kunlun Mountains (WKL) may be in a relatively stable state, although there are some gaps in previous research. Based on Landsat series data, topographic maps, SRTM and TanDEM-x data, this paper extracts detailed glacial area information and glacial mass balance during different time periods from 1970 to 2018. We found that, the total area of glaciers in the WKL decreased by 8.0 km2 from 1972 to 2018. The area decreased by 12.0 km2 from 1972 to 1991 and increased by 4.7 km2 from 2010 to 2018. Glacier surface elevation change results in the WKL showed that the overall glacier thickness slightly decreased from 1970 to 2016, with an average of 1.9 ± 1.0 m. The glaciers thinned by approximately 2.5 ± 1.0 m from 1970 to 2000, while from 2000 to 2016, the glaciers thickened approximately by 0.6 ± 1.0 m. Overall, the glaciers in the WKL showed very slight retreat. In addition, the mass changes of glaciers were affected by glacial surging.

DEM analysis of undrained cyclic simple shear test on saturated sand

DEM analysis of undrained cyclic simple shear test on saturated sand

DEM analyses of constant stress ratio compression and collapsibility tests on unsaturated structural loess

DEM analyses of constant stress ratio compression and collapsibility tests on unsaturated structural loess

DEM analyses of true triaxial and wetting tests on unsaturated structural loess

DEM analyses of true triaxial and wetting tests on unsaturated structural loess

A new index to characterize the segregation of binary mixture

In present study, we develop a new segregation index having both geometrical and physical significances, on the basis of segregation profile of granular bed. We carry out a DEM simulation to validate this index and analyze the segregation of binary mixture. The DEM analysis reveals that the segregation profile of granular bed subjected to vibration is in general in a reverse “N” mode, which tends to narrow and weaken as vibration continues. At a proper vibration amplitude, the reverse “N” pattern diminishes progressively and the overall segregation profile evolves into a three-line-segment pattern which stands for the ideal state of full segregation. A comparison analysis indicates that the new index proposed in this study is able to give a more proper estimation of segregation phenomenon for binary mixtures, as compared with other indices from the literature.

DEM analysis of some effects due to capillary forces in sands

In this paper, the Discrete Element Method is used to study the effect of capillary forces, in equilibrium with the ambient relative humidity, on the response of irregular arrangements of equal-sized spheres, simulating a fine uniformly graded quartz sand. The effect on the isotropic compression was investigated by applying an increase in total stress under constant relative humidity (wet and dry) and drying under different constant total stress values. The effect of the capillary forces on the shear strength was evidenced by the simulation of the instability of a cylindrical sand column due to drying.

Discrete element analysis of normal elastic impact of wet particles

The presence of liquids in particulate materials can have a significant effect on their bulk behaviour during processing and handling. It is well recognised that the bulk behaviour of particulate materials is dominated by the interactions between particles. Therefore, a thorough understanding of particle-particle interaction with the presence of liquids is critical in unravelling complex mechanics and physics of wet particulate materials. In the current study, a discrete element method for wet particulate systems was developed, in which a contact model for interactions with pendular liquid bridges between particles of different sizes was implemented. In order to evaluate the accuracy and robustness of the developed DEM, normal elastic impacts of wet particles with a wall were systematically analysed. It was shown that the DEM simulations can accurately reproduce the experimental observations reported in the literature. In addition, the DEM analysis was also in good agreement with the elastohydrodynamic model. It was further demonstrated that the rebound behaviour of wet particles is dominated by the Stokes number. There was a critical Stokes number, below which the particle will stick with the wall. For impacts with a Stokes number higher than the critical Stokes number, the coefficient of restitution increases as the stokes number increases for elastic particles. It was also found that the contact angle and surface tension played an insignificant role in the normal impact of wet particles, while the viscosity of the liquid has a dominant effect on the rebound behaviour.