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1.
A numerical simulation based on discrete element method (DEM) was conducted on the excavation and pushing processes of soil by a bulldozer blade. Soil contains water and the resistance acting on the bulldozer blade is largely influenced by the cohesive force due to liquid bridges formed among soil particles. In the present study, a cohesive bond force model proposed by Utili and Nova [5] was introduced in which the microscopic behavior of cohesive force was modeled analogously with macroscopic shear failure characteristics. The dependency on the magnitude of microscopic cohesive force was verified. The behavior of particles changed greatly by taking into account the cohesive bond force. The characteristic behavior of excavated soil aggregates, such as rolling motion and intermittent collapsing, were observed in front of the blade surface.  相似文献   

2.
We apply the Distinct Element Method (DEM) to analyze the dynamic behavior of soil. However, the conventional DEM model for calculation of contact forces between elements has some problems; for example, the movement of elements is too discrete to simulate real soil particle movement. Therefore, we modify the model to solve the difficulties. To investigate the validity of the modified model, we conduct an experiment in which soil is cut with a pendulum-typeblade, and simulate the soil loosening process with the modified DEM model. This paper presents details of the experimental apparatus and the comparison of soil behavior and energy absorption between the simulation and the experiment. Some characteristic phenomena of the experiment are reproduced in the simulation giving us confidence that the modified model is better than the conventional model for the simulation of soil behavior.  相似文献   

3.
颗粒形状对粗粒土的物理力学特性有着显著的影响。离散元法广泛应用于粗粒土宏观物理力学特性的细观机理研究。为了考虑颗粒形状的影响,亟待发展计算高效的离散元非球趋真颗粒模型。本文基于X射线CT扫描技术并结合数字图像处理技术,对光滑和棱角性两类典型粗粒土(鹅卵石与碎石)进行三维重构,并提出了两类趋真颗粒模型,分别采用扩展超椭球模型和球多面体模型进行趋真逼近;开展了两类颗粒试样的3D打印和单轴压缩试验,分析了配位数和局部孔隙率分布等细观特性;基于离散元开源程序SudoDEM开展了两类试样的离散元模拟,并将模拟细观分析结果与物理试验进行了对比。结果表明,提出的两类趋真颗粒模型能够较好地对粗粒土颗粒进行离散元建模。  相似文献   

4.
《Comptes Rendus Mecanique》2017,345(12):868-889
Due to increasing global energy demands, research is being conducted on the mechanical properties of methane hydrate-bearing soils (MHBSs), from which methane hydrate (MH) will be explored. This paper presents a numerical approach to study the mechanical properties of MHBSs. The relationship between the level of MH saturation and the interparticle bond thickness is first obtained by analyzing the scanning electron microscope images of MHBS samples, in which is the bridge connecting the micromechanical behavior captured by the DEM with the macroscopic properties of MHBSs. A simplified thermal-hydromechanical (THM) bond model that considers the different bond thicknesses is then proposed to describe the contact behavior between the soil particles and those incorporated into the discrete element method (DEM). Finally, a series of biaxial compression tests are carried out with different MH saturations under different effective confining pressures to analyze the mechanical properties of deep-sea MHBSs. The results of the DEM numerical simulation are also compared with the findings from triaxial compression tests. The results show that the macromechanical properties of deep-sea MHBSs can be qualitatively captured by the proposed DEM. The shear strength, cohesion, and volumetric contraction of deep-sea MHBSs increase with increasing MH saturation, although its influence on the internal friction angle is obscure. The shear strength and volumetric contraction increase with increasing effective confining pressure. The peak shear strength and the dilation of MHBSs increase as the critical bond thickness increases, while the residual deviator stress largely remains the same at a larger axial strain. With increasing the axial strain, the percentage of broken bonds increases, along with the expansion of the shear band.  相似文献   

5.
针对铁路道床有砟-无砟过渡段的结构特点,采用离散元-有限元耦合模型分析散体道砟和无砟道床间过渡段的动力特性。散体道砟道床和无砟道床分别采用离散元方法 DEM和有限元方法 FEM模拟,而在过渡段将道砟颗粒嵌入无砟道床以增加道砟颗粒与无砟道床间的咬合力,并在离散元和有限元耦合区域实现了力学参数的传递。采用以上DEM-FEM耦合方法对有砟-无砟道床及其过渡段在列车荷载作用下的沉降过程进行了数值分析。计算结果表明,离散元方法中道砟颗粒间的力链呈现非对称梯形分布,其与有限元方法中的应力分布趋势一致;采用嵌入式道砟颗粒的方法可以增加有砟-无砟过渡段道砟间的咬合力,有效约束道砟颗粒的位移,减少有砟-无砟道床间的沉降差异。本文计算模型可以合理地分析有砟道床的力链分布以及无砟道床的应力分布,确定列车荷载下道床有砟-无砟过渡段的动力学行为。  相似文献   

6.
Leakage from underground pipes could result in foundations being undermined and cause damage to adjacent infrastructure. Soil particles surrounding the leaking area could be mobilised, displaced, and even washed out of the soil matrix by the leaking fluid, generating a void or cavity. A two-dimensional simulation using a coupled discrete element method and lattice Boltzmann method (DEM–LBM) has been used to investigate the behaviour of a soil bed subject to a locally injected fluid, which represents a leak in a pipe. Various values of inter-particle surface energy were also adopted to model the mechanical effects of cohesive particles. The results suggest that the inter-particle surface energy greatly influences the bed response with respect to the leaking fluid, including the excess pressure initiating the cavity, the cavity shape and its evolution rate.  相似文献   

7.
The discrete element method (DEM), developed by Cundall and Strack (1979) to solve geomechanical problems, is used to simulate the mechanical behavior of granules. According to the DEM, an individual granule can be modeled as a realistic mechanical system consisting of primary particles bonded by interaction forces.Granulometric properties of the model material, zeolite 4A, have been measured to determine their macro properties. To investigate the compression behavior, a compression test was performed using a strength tester on single granules between two pistons. A modeled granule consisting of more than 22,000 primary particles was generated. The micro properties of the modeled granule have been precisely set to allow its macro properties to be equivalent to the macro properties of zeolite 4A granules. To calibrate the mechanical properties, diametrical compression was simulated using two rigid walls stressed at a constant stressing velocity. The force–displacement curve of the modeled granule at compression has been calibrated by the experimental curve of zeolite 4A.  相似文献   

8.
The multi-scale characteristics of clusters in a fast fluidized bed and of agglomerates in a fluidized bed of cohesive particles are discussed on the basis of large amounts of experiments.The cluster size and concentration are dominated by the local voidage of the bed.A cluster consists of many sub-clusters with different sizes and discrete par-ticles,and the sub-cluster size probability density distribution appears as a negative exponential function.The agglom-erates in a fluidized bed of cohesive particles also possess the multi-scale nature.The large agglomerates form a fixed bed at the bottom,the medium agglomerates are fluidized in the middle,and the small agglomerates and discrete parti-cles become the dilute-phase region in the upper part of the bed.The agglomerate size is mainly affected by cohesive forces and gas velocity.The present models for prediction the size of clusters and agglomerates can not tackle the in-trinsic mechanism of the multi-scale aggregation,and a challenging problem for establishing mechanistic model is put forward.  相似文献   

9.
A mechanical model of soil is constructed using the Distinct Element Method (DEM) which makes it possible to analyze the discontinuous property of soil. To discuss the applicability of the soil model by the DEM, a bar penetration test was conducted and the result was compared with the simulation results. From the results of the behavior of elements, it could be said that the mechanical model by the DEM could well simulate the discontinuous behavior of soil and the parameters used in the simulation play important roles to make the soil model useful. As for the penetrating resistance, some problems which lie in the present DEM model are discussed and the key to solving these problems is indicated. Moreover, the method to determine the time interval used in the DEM simulations is mentioned in terms of the stability of the solution in the calculation.  相似文献   

10.
Numerical and experimental direct shear tests for coarse-grained soils   总被引:3,自引:0,他引:3  
The presence of particles larger than the permissible dimensions of conventional laboratory specimens causes difficulty in the determination of shear strength of coarse-grained soils. In this research, the influence of particle size on shear strength of coarse-grained soils was investigated by resorting to experimental tests in different scale and numerical simulations based on discrete element method (DEM). Experimental tests on such soil specimens were based on using the techniques designated as "parallel" and "scalping" to prepare gradation of samples in view of the limitation of laboratory specimen size. As a second approach, the direct shear test was numerically simulated on assemblies of elliptical particles. The behaviors of samples under experimental and numerical tests are presented and compared, indicating that the modification of sample gradation has a significant influence on the mechanical properties of coarse-grained soils. It is noted that the shear strengths of samples produced by the scalping method are higher than samples by the parallel method. The scalping method for preparing specimens for direct shear test is therefore recommended. The micromechanical behavior of assemblies under direct shear test is also discussed and the effects of stress level on sample behavior are investigated.  相似文献   

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