Discrete Element Method Analysis Research Articles

Exploring the micro-to-macro response of granular soils with real particle shapes via μCT-aided DEM analyses

This contribution provides high fidelity images of real granular materials with the aid of X-ray micro computed tomography (μCT), and employs a multi-sphere representation to reconstruct non-spherical particles. Through the discrete element method (DEM) simulations on granular samples composed of these non-spherical clumps, the effect of particle shape on the macroscopic mechanical response and microscopic soil fabric evolution is examined for soil assemblies under triaxial compression. Simulation results indicate that materials with more irregular particles tend to show higher shear resistance in both peak and critical states, while exhibiting higher void ratio under isotropic loading conditions and in the critical state. The proposed critical state parameters for describing the sensitivity of the mean coordination number to confining pressures are larger as particles become more irregular. At a microscopic level of observation, directional and scalar parameters of particle contacts are sensitive to predefined particle asperities. More irregular materials appear to exhibit higher fabric anisotropy regarding particle orientation in the critical state, while branch vector is affected by both contact modes and particle shape. The critical stress ratio from the simulation results is validated by comparing with experimental results, and further found to be linearly linked to the shape-weighted fabric anisotropy indices.

DEM analysis of the dynamic characteristics of QH-E lunar soil simulant under cyclic triaxial tests

In this paper, cyclic triaxial tests are performed by using discrete element method (DEM) to investigate the dynamic behaviors of QH-E lunar soil simulant. The influences of number of cycles, loading frequency, waveform, cyclic stress ratio (CSR) and confining pressure on the dynamic behaviors of lunar soil simulant are discussed. The results indicate that the axial strain and dynamic modulus first increase and then tend to be stable with increasing number of cycles. The dynamic modulus increases with increasing the loading frequency, while the axial strain decreases. The damping ratio is not particularly sensitive to the confining pressure and CSR, it only decreases slightly with increasing confining pressure or decreasing CSR. Under the same conditions, rectangular wave dynamic load can produce a larger axial strain and a smaller dynamic modulus than those of sine and triangular waves, and a higher loading frequency will lead to a higher dynamic modulus and a lower axial strain, these characteristics are consistent with other lunar soil simulants and sandy soils tested in the experiment. However, the effect of confining pressure on the dynamic modulus depends on the magnitude of the CSR. For the lower CSR (CSR<0.6), the dynamic modulus increases with increasing confining pressure. While for the higher CSR(CSR>0.6), the dynamic modulus decreases significantly with increasing confining pressure, which demonstrates the unique dynamic characteristics that differs from other lunar soil simulants and sandy soils, and shows the importance of considering the magnitude of the CSR under cyclic triaxial tests.

Discrete Element Method Analyses of Bond Degradation Evolutions for Cemented Soils

The degradation of soil bonding, which can be described by the evolution of bond degradation variables, is essential in the constitutive modeling of cemented soils. A degradation variable with a value of 0/1.0 indicates that the applied stress is completely sustained by bonded particles/unbounded grains. The discrete element method (DEM) was used for cemented soils to analyze the bond degradation evolution and to evaluate the degradation variables at the contact scale. Numerical cemented soil samples with different bonding strengths were first prepared using an advanced contact model (CM). Constant stress ratio compression, one-dimensional compression, conventional triaxial tests (CTTs), and true triaxial tests (TTTs) were then implemented for the numerical samples. After that, the numerical results were adopted to investigate the evolution of the bond degradation variables BN and B0. In the triaxial tests, B0 evolves to be near to or larger than BN due to shearing, which indicates that shearing increases the bearing rate of bond contacts. Finally, an approximate stress-path-independent bond degradation variable Bσ was developed. The evolution of Bσ with the equivalent plastic strain can be effectively described by an exponential function and a hyperbolic function.

DEM simulation and optimization of crushing chamber shape of gyratory crusher based on Ab-t10 model

To study and optimize the crushing chamber performance of the gyratory crusher, the impact of the crushing chamber shape on the gyratory crusher performance is explored in this paper. The discrete element method (DEM) analysis model of ore particle and gyratory crusher is established, where ore particle crushing is realized based on the Ab-t10 breakage model, and its validity is verified based on actual working conditions. On this basis, the performance of the gyratory crusher under different crushing chamber shapes is studied by combining the DEM simulation with the response surface method (RSM), and the performance prediction model is obtained based on multiple nonlinear regression. Further, the productivity is considered as the main optimization objective, the mass percentage of effective particles and the crushing force are used as auxiliary optimization objectives. The multi-objective optimization is implemented and the optimized effects are analysed by DEM simulation, and the optimized quartic equation coefficients of the concave curve are obtained. Finally, the results show that the productivity, mass percentage of effective particles, and crushing force are increased to varying degrees. Meanwhile, the clogged layer area increases to some extent, which promotes the crushing of ore particles.

Assessment of shear band evolution using discrete element modelling

PurposeThe objective of this paper is to quantitatively assess shear band evolution by using two-dimensional discrete element method (DEM).Design/methodology/approachThe DEM model was first calibrated by retrospectively modelling existing triaxial tests. A series of DEM analyses was then conducted with the focus on the particle rotation during loading. An approach based on particle rotation was developed to precisely identify the shear band region from the surrounding. In this approach, a threshold rotation angle ω0 was defined to distinguish the potential particles inside and outside the shear band and an index g(ω0) was introduced to assess the discrepancy between the rotation response inside and outside shear band. The most distinct shear band region can be determined by the ω0 corresponding to the peak g(ω0). By using the proposed approach, the shear band development of two computational cases with different typical localised failure patterns were successfully examined by quantitatively measuring the inclination angle and thickness of shear band, as well as the microscopic quantities.FindingsThe results show that the shear band formation is stress-dependent, transiting from conjugated double shear bands to single shear band with confining stress increasing. The shear band evolution of two typical localised failure modes exhibits opposite trends with increasing strain level, both in inclination angle and thickness. Shear band featured a larger volumetric dilatancy and a lower coordination number than the surrounding. The shear band also significantly disturbs the induced anisotropy of soil.Originality/valueThis paper proposed an approach to quantitatively assess shear band evolution based on the result of two-dimensional DEM modelling.

Wear Analysis of NiTi Sand Screens Using Altair Discrete Element Method.

This research explores discrete element method analysis to investigate the wear of NiTi Sand Screens in comparison to traditional materials. The study utilized Altair EDEM v2022.2 software and employed Oka and Archard models to simulate the wear behavior of Nitinol, a well-established Shape Memory Alloy (SMA). The mechanical properties considered include Poisson's ratio, solid density, shear modulus, and Young modulus. Results indicate significantly higher wear values and deformations with the Oka model compared to negligible wear with the Archard model. The Oka model's emphasis on impact as the primary wear mechanism, supported by high normal cumulative energy, better represents sand screen wear phenomena. Additionally, this study indicates that factors such as particle size distribution and normal and tangential cumulative contact energy hold potential as predictors of wear response and characteristics. The Oka model demonstrated that NiTi exhibited reduced wear losses compared to SUS630 and Cr-Mn white cast iron, both of which are recognized for their high toughness when subjected to an impact load. Experimental analysis validated the simulation findings with morphological and graphical erosion plots. The limitation of observing the shape memory effect through DEM (discrete element method) simulation was acknowledged. Recommendations include characterizing post-wear microstructural changes, exploring the influence of temperature on wear behavior, and further research to refine wear models and understand SMA sand screen responses.

Development of a New Generation High Crushing Capacity Jaw Crusher with an Automatically Adjusted Closed Side Settings

The design and development of a new generation high crushing capacity jaw crusher, developed for the first time in Turkey and whose Closed Side Settings (CSS) may be automatically adjusted hydraulically, were investigated in this study. The calculations for the crusher developed for this purpose were included in the paper. The design modifications made to expand the crusher's jaw stroke from 27 mm to 40 mm were documented, and the capacity increase resulting from this was theoretically calculated and proven by a wide range of field tests conducted after the jaw crusher was manufactured. Field testing and their findings were also thoroughly covered in the paper. The forces on the crusher jaw and bearings, the crusher body geometry and crusher material (via fatigue analysis), and the dynamic performance of the system (via vibration analysis of the carrier system) were examined as the outcome of the FEM (Finite Element Method) and DEM (Discrete Element Method) analyses performed after the theoretical calculations. With improvements made based on the findings gained, the theoretical and practical harmony of the created jaw crusher system was realized. Field testing has proven that the adjustment procedure takes no more than 3 minutes and requires no human participation. As a result of this research, a patent application for the created automation algorithm was filed.

DEM analysis of the effect of geocell on splitting tensile behavior of asphalt mixture based on multi-phase model

Herein, an investigation was conducted upon the reinforcement of geocell on the splitting tensile process of asphalt mixture using laboratory tests and the discrete element method (DEM). Micromechanical modeling of geocell-reinforced asphalt mixture and virtual splitting tensile test was built using PFC3D based on the vital material features and mechanical properties of different ingredients (e.g., the three-dimensional irregular shapes and elastic properties of coarse aggregates and geocell, the viscoelastic properties of asphalt mastic, and the random distribution of air voids in asphalt mastic). Meanwhile, the parameters of the DE model were determined by splitting tensile test, and the effects of geocell on the splitting tensile process of contact force, displacement and stress were evaluated through the virtual splitting test. The results indicated the efficiency of the built DE model and virtual test in effectively predicting the splitting process of geocell-reinforced asphalt mixture. Besides, geocell acted mainly in the falling stage of the load-displacement curve during the splitting process, where the contact force distribution of each phase component shifted from the lower to the higher range, and the effect between coarse aggregates was the greatest, followed between coarse aggregate and asphalt mastic, with the least within asphalt mastic. Further, the maximum displacement of asphalt mixture in the X and Y directions was reduced by the geocell, significantly constraining the coarse aggregate and mastic in geocell-reinforced layer. In addition, the stress in the splitting center of asphalt mixture was greater than that at the sides, and the stress within the geocell of the reinforced layer was significantly lower compared to the unreinforced layer, especially in the falling stage. Overall, the present results forge a theoretical basis for the tensile performance of geocell-reinforced asphalt mixture from the microscopical perspective.

Experimental study and discrete element method analysis of impact of vibration on pebble packing

To develop tritium breeding technology for fusion reactors, Korea actively participated in the ITER Test Blanket Module (TBM) program, focusing on the development of a ceramic breeder-type TBM. The challenge was to introduce pebbles into the TBM without causing any damage to them. This study conducted experiments and Discrete Element Method (DEM) analyses to optimize the pebble-filling process for breeding blanket development. Even when facing obstacles such as grooved shapes on the walls of the pebble-filled space, these grooves did not significantly reduce the packing ratio. Vibrating the pebbles proved essential to increase the pebble packing ratio. Both experiments and DEM analyses confirmed an increase in pebble packing when vibration is applied. The study also investigated the impact of the timing of vibration application. It is better to vibrate after the pebble injection is done during injection to increase the pebble packing ratio. This approach increases the pebble packing ratio, but it also makes additional empty space. Consequently, maintaining continuous vibration from the initiation to the completion of the injection process can increase the packing ratio without the need to repeat the injection process to fill the empty space.

CFD–DEM modelling and analysis of proppant transportation inside tortuous hydraulic fractures

Hydraulic fractures in unconventional gas/oil and tight reservoirs generally have tortuous shapes. This paper presents a numerical study of the proppant transportation and distribution in tortuous hydraulic fractures. This is done by combining computational fluid dynamics (CFD) with discrete element method (DEM). The CFD-DEM model is validated by comparing the numerical results with the experimental measurements of proppant transportation and distributions in single and multiple straight fractures. Via the model, the effect of tortuosity on proppant transportation is studied based on tortuous fractures constructed according to an actual fracture profile. The numerical results show that the packing pattern has a trapezoid shape as the fracture tortuosity varies from 0.6 to 1. It becomes triangular in the tortuosity range of 0–0.4. The horizontal distance and the vertical height of the proppant bed exhibit different trends against fracture tortuosity.

Multi-disciplinary characterization of shrinkage effects in Opalinus clay

Due to its low hydraulic permeability and several beneficial mechanical properties, Opalinus Clay formation (OPA) is considered as a potential host rock for high-level radioactive waste disposal. However, several factors during the excavation and operational stages can endanger the long-term safety of the repositories. One of the major safety concerns in the underground geological repositories includes the formation of shrinkage-induced cracks [1].  Shrinkage-induced cracks, i.e., desiccation cracks, are a result of the underground opening being exposed to lower relative humidity (RH) levels during seasonal changes and subsequent shrinkage deformation. Over the last two decades, OPA has been extensively investigated by several in-situ experiments conducted at the Mont Terri Underground Rock Laboratory (URL) in Switzerland [2]. In particular, the recently established cyclic deformation (CD-A) experiment is aimed at the investigation of the coupled hydro-mechanical processes in the sandy facies of OPA due to the seasonal changes and variations in RH [3]. In this study, to further investigate the mechanical parameters of OPA under various climatic conditions and to capture potential desiccation cracking scenarios, a multi-disciplinary approach, including experimental analysis and numerical simulation, has been adopted. In this regard, the required samples for laboratory tests were taken from drilled cores near the CD-A experiment. Additionally, the observations in CD-A regarding the onset and propagation of desiccation fracturing were used as validation point for verification of the employed numerical method.&#x0D; In order to characterize the RH-dependent mechanical parameters of the OPA, a customized desiccator cell has been configured and set up at the geomechanics and geotechnics laboratory of CAU.  The concept of a humidity-controlled rock laboratory test setup originates from [4]. The experimental setup, as well as its schematic representation, is shown in Figure 1(a). The components of the customized desiccator cell can be divided into four parts, including an isolated epoxy glass cell equipped with RH and temperature sensors, a loading apparatus, a salt bath and a micro-camera tube. The experimental layout contains two distinct stages, namely the equilibrium and loading stages. During the first stage and prior to the onset of mechanical loading, the sample is placed inside the cell, where it is allowed to equilibrate with a certain level of RH. Based on the initial water content of the sample and RH in the cell, the equilibrium stage can last 7-10 days. The RH inside the cell, covering the range between 0.19 and 0.88, was achieved and maintained by employing various saturated salt solutions. In this study, the above-mentioned methodology is employed to investigate the strength characteristics of the OPA under different humidity conditions. For such a purpose, a series of semi-circular three-point bending experiments (SCB) has been conducted. Furthermore, given the relative angle between the loading direction and plane of isotropy, denoted as , three types of samples with  were considered to account for the anisotropic effects. The experimental observations in terms of peak loads obtained during the loading stage against the varying RH in the cell are illustrated in Figure 1(b). In addition to the general decreasing trend for material toughness as a result of increasing RH, the remarkable effect of structural anisotropy on material strength can be seen. It should be noted that, the observed deviation from the overall trend for peak load response of certain samples can be attributed to the generation of the micro-defects in samples during the preparation or the drilling processes, which can lead to alterations in the mechanical properties of the samples.&#x0D; To further investigate the shrinkage effects and mechanisms of desiccation fracturing observed in OPA during experimental and field analyses, we utilized and extended the Finite Discrete Element Method (FDEM). In this regard, a hydro-mechanically coupled framework based on the principles of Richards Mechanics is developed to account for the flow in the variably saturated porous medium. The FDEM was originally developed by Munjiza et al. [5]. By combining the principles of the Discrete Element Method (DEM) and Finite Element (FE) analysis, the FDEM is capable of capturing the transition from a continuous to a discontinuous state through the simulation of fracturing and fragmentation processes [6]. To realize the anisotropic mechanical response in OPA, a transversely isotropic stress-strain constitutive law was implemented. Additionally, a strength criterion for each cohesive element was considered based on its relative angle with the macroscopic bedding direction [7].&#x0D; In order to consider the variably saturated porous media flow within the framework of FDEM, a vertex-centered finite volume scheme is adopted. Based on this approach, a dual grid of polygonal control volumes is subjected to the conservation of the fluid phase. The adopted mass balance equation of water can be expressed as follows &#x0D; where  and  are the saturation and pore water pressure, respectively.  is the Biot’s coefficient,  is the porosity and  is the water bulk modulus. In Eq. 1, denotes the fluid flux vector. The flow rate vector, , is evaluated based on the unsaturated Darcy flow law. The Van Genuchten constitutive law was used for the definition of the hydraulic behavior in an unsaturated porous medium where the permeability tensor and saturation state are functions of pressure head [8]. The hydro-mechanical coupling was realized based on the principle of effective stress and achieved by adopting a staggered coupling scheme. The methodology was verified against the available benchmarks in the literature. To capture the desiccation cracking in field scale, a model consisting of a 2D cross section of the CD-A experiment was also considered. The required material properties for the numerical model were obtained from experimental results. In complete agreement with field observation in the CD-A experiment, the desiccation cracks start to develop around the underground opening at RH between 97~98%.&#x0D; This paper presented a multi-disciplinary approach for the characterization of the shrinkage effects in OPA. In this regard, a combination of experimental analysis and numerical modelling techniques has been employed. The experimental work provided a better understanding of the anisotropic mechanical properties of OPA under different humidity conditions. The developed coupled formulation in the FDEM framework has proven to be successful in capturing desiccation fracturing mechanisms in the field scale. The presented methodology would facilitate further investigation of scenarios in which desiccation fracturing is involved.

DEM analysis of wear evolution and its effect on the operation of a lab-scale HPGR mill

Wear due to compression and abrasion from particles is a critical issue for high pressure grinding rolls (HPGR) mills. Understanding the evolution of wear provides useful insight on its mechanisms and helps to mitigate the issue so mills are operated at their optimal states. This work presented numerical simulations based on the discrete element method (DEM) to analyse the formation and evolution of wear of a lab-scale HPGR mill and to investigate how wear affects mill performance and particle breakage. By coupling the DEM model with the Archard wear model and surface re-meshing, the simulated wear patterns were comparable with those observed in practice, showing a parabolic wear profile wear along the rolls with more severe wear in the centre. In addition, the rear part of the stud, compared with the middle and front parts, experienced more significant wear due to the combined effect of compression and abrasion. While increasing wear had no visible effect on throughput, it reduced mill power draw due to weaker compressive force from the rolls to particles. Furthermore, analysis on particle breakage showed that increasing wear reduced particle breakage and produced coarser products. Increasing wear also caused less damage to particles, suggesting more cycles are required to achieve targeted products.

Analysis of spatial damage characteristics of rock under multiple high-voltage pulse discharges: I. Cross-section characteristics

Rock breaking by high-voltage pulse discharge (rock breaking by high-voltage pulse discharge, RHPD) is an efficient technology for rock breaking. A single discharge will lead to the initiation or expansion of cracks inside the rock, and the expansion of cracks after multiple discharges will lead to the destabilization of the rock and finally produce a fractured zone. Because of the difficulty in quantifying the spatial damage characteristics of the fractured zone, in this paper, based on the discrete element method and theoretical analysis, the spatial damage model (spatial damage model, SDM) of rock is established. For a typical liquid-solid combination, from the microscopic point of view, the damage characteristics of the fractured zone on the radial cross-section of the plasma are quantified. The changing characteristics of the damage characteristics were analyzed for multiple discharges. In addition, an experimental platform has been built, and the accuracy of the SDM has been verified by the experimental results. The results show that the increase in the discharge distance will improve the deposition energy and crushing effect, and will also improve the accuracy of the model. The findings of this paper provide a technical reserve for the application of RHPD.

DEM analysis of the influence of stirrer design on die filling with forced powder feeding

Die filling is a critical stage during powder compaction, which can significantly affect the product quality and efficiency. In this paper, a forced feeder is introduced attempting to improve the filling performance of a lab-scale die filling system. The die filling process is analysed with a graphics processing units (GPU) enhanced discrete element method (DEM). Various stirrer designs are assessed for a wide range of process settings (i.e., stirrer speed, filling speed) to explore their influence on the die filling performance of free-flowing powder. Numerical results show that die filing with the novel helical-ribbon (i.e., type D) stirrer design exhibits the highest filling ratio, implying that it is the most robust stirrer design for the feeder configuration considered. Furthermore, die filling performance with the type D stirrer design is a function of the stirrer speed and the filling speed. A positive variation of filling ratio (ηf>0%) can be ensured over the whole range of filling speed by adjusting the stirrer speed (i.e., increasing the stirrer speed). The approach used in this study can not only help understand how the stirrer design affects the die filling performance but also guide the optimization of feeder system and process settings.

DEM simulations on the influence of carbonate precipitation on liquefaction mitigation of sand

Microbially induced carbonate precipitation (MICP) is an effective method to mitigate liquefaction of sands under cyclic shear loading. In this paper, discrete element method (DEM)-based simulations of the cyclic direct simple shear (CyDSS) tests are carried out using a three-dimensional shear box geometry to evaluate the liquefaction resistance of untreated, MICP-cemented, and reconstituted sands. A six-parameter contact model previously used for undrained and drained triaxial tests on sand is used in the DEM analysis. Verification and validation of the DEM model is implemented through modeling of experimental CyDSS results on loose Fraser River sand at several values of cyclic stress ratios (CSR). The DEM model parameters for untreated and microbially treated Ottawa 20–30 sand are obtained by matching the simulated deviatoric stress and excess pore pressure from strain-controlled undrained isotopically consolidated triaxial compression tests. The DEM model is shown to be capable of accurately representing the cyclic strength curves for untreated, treated, and treated but reconstituted sand using parameters derived from the triaxial test data. The simulated stress path, shear strain evolution, and the evolution of coordination number are used to further examine the effect of MICP on liquefaction in CyDSS tests. The DEM model can be used to design cementation levels and develop cyclic strength curves for different types of sands to aid engineers in designing liquefaction mitigation strategies using MICP.

Optimization of the Fluted Force-Feed Seeder Meter with the Helical Roller Using the Discrete Element Method and Response Surface Analysis

The seed metering process of a fluted force-feed seeder was simulated using the Discrete Element Method and its parameters optimized using the Box–Behnken Design of Experiments and the Response Surface Method. The rotational speed of the feed roller, the lead (helix) angle of the flutes, and the number of flutes were the independent variables, while the response value was the seeding uniformity index. Two regression models were investigated, and the following conclusions drawn. For the flute lead angle between 0 and 10 degrees, and the number of flutes between 10 and 14, it was found that the number of flutes and the lead angle influenced the seeding performance the most, with the order of importance being the (i) number of flutes, (ii) lead angle and (iii) roller speed. For the flute lead angle between 5 and 15 degrees, and the number of flutes between 12 and 16, it was found that the roller speed and the number of flutes influenced the seeding performance the most, with the order of importance being the (i) roller speed, (ii) number of flutes and (iii) flute lead angle. The two regression models were then minimized for the seeding uniformity index and the corresponding optima verified experimentally on a conveyor belt test stand fitted with an image recognition system.

Experimental and numerical simulation study on flow behavior of asphalt mixture using smart aggregate

A meso-scale mechanical analysis approach, which is essentially based on the use of smart aggregate sensor, was employed to inquire the dynamic responses of smart aggregate in cold recycled asphalt mixtures during gyratory compaction, including as well an investigation over the critical influence factors. The discrete element method (DEM) was further applied to study the interaction behaviors of smart aggregate with the surrounding particles. The laboratory test results showed that smart aggregate is an effective method to monitor the contact force and rotation variation between the aggregates, and the changes in the mechanical and physical properties of the mixtures can be characterized by the monitoring results of smart aggregate. In addition, the results of DEM analyses show that the mixtures with 55% coarse aggregates have higher normal force and lower kinetic energy during gyratory compaction, revealing the influence mechanism of the effect of coarse aggregate content on smart aggregate monitoring results at the meso-scale.

Comparative Study of the Rock-breaking Mechanism of a Disc Cutter and Wedge Tooth Cutter by Discrete Element Modelling

The operation of a shield tunnel boring machine (TBM) in a high-strength hard rock stratum results in significant cutter damage, adversely affecting the thrust and torque of the cutter head. Therefore, it is very important to carry out the research on the stress characteristics and optimize the cutter parameters of cutters break high-strength hard rock. In this paper, the rock-breaking performance of cutters in an andesite stratum in the tunnel of Qingdao Metro Line No. 8 was investigated using the discrete element method and theoretical analysis. The rock-breaking processes of a disc cutter and wedge tooth cutter were simulated by software particle flow code PFC3D, and the rock-breaking degree, stress of the cutter, and rock-breaking specific energy were analyzed. The rock damage caused by the cutter in a specific section was divided into three stages: the advanced influence, crushing, and stabilizing stages. The rock-breaking degree and the tangential and normal forces of the wedge tooth cutter are larger than that of the disc cutter under the same conditions. The disc cutter (wedge tooth cutter) has the highest rock-breaking efficiency at a cutter spacing of 100 mm (110 mm) and a penetration depth of 8 mm (10 mm), and the rock-breaking specific energy is 11.48 MJ/m3 (12.05 MJ/m3). Therefore, two types of cutters with different penetration depths or cutter spacing should be considered. The number of teeth of wedge tooth cutters can be increased in hard strata to improve the rock-breaking efficiency of the shield. The research results provide a reference for shield cutterhead selection and cutter layout in similar projects.

DEM Analysis of Dynamic Evolutions of Lateral Soil Arching in Sandy Soil

For landslide mitigation, stabilizing piles are widely adopted in geotechnical engineering practice. The formation of soil arching between stabilizing piles can greatly mitigate the lateral spreading of sandy soil, and complementarily, evidence demonstrates that the sandy soil properties have a significant influence on the soil arching process. Thus, this paper focuses on investigating the lateral arching evolution behaviors in both dense and loose sands. A discrete element method (DEM) involving the servo-mechanism that plays a role in quantitatively controlling the translational velocity of selected walls when a desired force is to be applied or maintained was carried out to simulate the dynamic evolutions of the lateral soil arching process. The double-arch model is proposed to illustrate the end-bearing arch and frictional arch to analyze soil arching effects separately. Results indicate that the macrobehaviors and microbehaviors of lateral soil arching in dense and loose sands are initially distinct but ultimately similar. The arching mechanism is also illustrated by fabric analysis and coordination numbers. In general, the lateral arching evolutions in both dense and loose sands can be divided into three evolutionary stages as the loading displacement increases, which are similar to the strain-hardening and strain-softening phenomenon, respectively. Similarly, a unique arching process of forming-breaking-forming is identified by the use of particle trace. Moreover, multiple two-dimensional DEM models at different depths are superimposed vertically to study the three-dimensional soil arching. Based on the parametric studies, the loading velocity and pile spacing ratio have a preponderant influence on the development of soil arching, whereas the influence of the depth and confining stress is almost negligible. Additionally, the distribution of horizontal thrust has been determined by monitoring the stabilizing pile-based arching foot at different locations and the distribution of shear resistance is found to be approximately triangular.

A Comparative Computational Investigation on the In-Plane Behavior and Capacity of Dry-Joint URM Walls

ABSTRACT Predicting the lateral load-carrying capacity of dry-joint unreinforced masonry (URM) walls is often challenging due to the complex interactions between the governing parameters (i.e. geometrical and mechanical properties). The capacity and behavior of dry-joint URM walls depend on boundary conditions, size and location of the openings, bond pattern, vertical load, and aspect ratio, among other factors. In this context, the present research investigates the effect of bond pattern, aspect ratio, vertical load, and boundary condition on the in-plane (IP) behavior and capacity. Two computational methods, the discrete element method (DEM) and micro limit analysis (micro LA), are employed. Through a comprehensive parametric assessment, the result indicates a good agreement between the two approaches. The computational investigations underline the direct relationship of the IP capacity of walls with respect to aspect ratio and applied vertical pressure. Furthermore, fixed-no rotation boundary condition is associated with the increased IP capacity. Finally, a simple analytical equation is proposed to predict the lateral capacity of dry-joint URM walls.