共查询到20条相似文献，搜索用时 20 毫秒
1.
3D analysis of kinematic behavior of granular materials in triaxial testing using DEM with flexible membrane boundary 总被引：2，自引：2，他引：0
This paper describes the constitutive behavior and particle-scale kinematics of granular materials in three-dimensional (3D) axisymmetric triaxial testing using discrete element method (DEM). PFC3D code was used to run the DEM simulations using a flexible membrane boundary model consisting of spherical particles linked through flexible contact bonds. The overall deformation behavior of the specimen was then compared with the specimen with rigid boundary and experimental measurements. Computed tomography was used to track the evolution of particle translation and rotation within a laboratory triaxial specimen in 3D. The DEM model of the flexible membrane specimen successfully predicted the stress–strain behavior when compared with laboratory experiment results at different confining pressures. The DEM results showed that the rigid specimen applies a uniform deformation and leads to non-uniformities in the confining stress along the particle-boundary interface in the lateral direction. In contrast, the flexible specimen better replicates the uniformly applied confining stress of a laboratory triaxial experiment. The 3D DEM simulations of the specimen with flexible membrane overpredicted particle translation and rotation in all directions when compared to a laboratory triaxial specimen. The difference between the particle translation and rotation distributions of DEM specimens with rigid and flexible membrane is almost negligible. The DEM specimen with flexible membrane produces a better prediction of the macroscopic stress–strain behavior and deformation characteristics of granular materials in 3D DEM simulations when compared to a specimen with rigid membrane. Comparing macroscale response and particle-scale kinematics between triaxial simulation results of rigid versus flexible membrane demonstrated the significant influence of boundary effects on the constitutive behavior of granular materials. 相似文献
2.
月壤双轴试验的剪切带离散元数值分析 总被引：2，自引：0，他引：2
土体的破坏问题一般都是从其剪切带入手进行研究的。针对真实月壤所处的环境（无水、低重力场、低气压等）和内摩擦角较大的特点,采用最近提出的1种考虑粒间抗转动作用与粒间范德华力2个因素的月壤散粒体力学接触模型,用离散单元法模拟了柔性边界条件下月球环境（含范德华力）与地球环境（不含范德华力）2种试样的双轴压缩试验,通过试样局部变形、速度场、孔隙比及转动场的变化情况研究了2种试样剪切带形成与发展。研究结果表明,剪切带的形成是试样内部应变局部化的结果,同时也伴随着试样内部颗粒相对转动的局部化,月面环境对试样的破坏形式与性状（剪切带的倾角及厚度）有显著的影响,探月工程中必须考虑到月面环境对月壤力学性质的影响。 相似文献
3.
高速铁路CFG桩复合地基柔性载荷试验研究 总被引：1，自引：0，他引：1
高速铁路建设的迅速发展及高速铁路对路基沉降的严格要求,CFG桩在高速铁路路基的处理上得到大量运用。但铁路工程对路基的作用原理与工民建工程对地基的作用原理有本质的区别,工民建房屋建筑荷载通过基础对地基施加刚性荷载,而铁路路基直接承受上部路堤的自重和列车运行产生的柔性荷载。高速铁路CFG桩复合地基的设计都是根据工民建行业的设计理论进行,其试验结果必然与实际情况存在偏差。本文着手研究适合于高速铁路复合地基的柔性载荷试验方法,模拟高速铁路柔性加载的特性,通过数值分析对比了刚性荷载和柔性载荷作用下CFG桩复合地基的桩、土应力、位移分布情况;通过现场载荷试验对设计方案进行了验证,研究了高速铁路CFG桩复合地基的承载力特性,结果证明柔性载荷试验是可行的,能合理的模拟高速铁路CFG桩复合地基承载特性,可为柔性基础下CFG桩复合地基的设计提供基础。 相似文献
4.
Capturing strain localization in reinforced soils 总被引：2，自引：1，他引：1
Lade’s single hardening soil model with Cosserat rotation embodied in the finite element method is employed to investigate
the behavior of geosynthetic reinforced soils with special attention to the development of shear banding. The ability of the
finite element model to detect shear banding in a reinforced soil is examined against three high quality small-scale laboratory
plane strain tests on Toyoura sand with and without reinforcement. These three tests were chosen because of the clear failure
surfaces that developed in the soil during loading. The FEM analyses were able to reasonably simulate the plane strain laboratory
tests including both unreinforced and reinforced cases. The FEM analyses gave reasonably good agreement with the experimental
results in terms of global stress–strain relationships and shear band occurrences. Furthermore, and based on FE analyses of
a hypothetical geosynthetic reinforced soil (GRS) retaining wall, it is shown that the geosynthetic reinforcements are very
effective in hindering the formation of shear bands in GRS retaining walls when small spacing between the reinforcement layers
was used. When used properly, the geosynthetic reinforcements made the soil behave as a truly reinforced mass of considerable
stiffness and strength. 相似文献
5.
Methane hydrate (MH, also called fiery ice) exists in forms of pore filling, cementing and load-bearing skeleton in the methane hydrate bearing sediment (MHBS) and affects its mechanical behavior greatly. To study the changes of macro-scale and micro-scale mechanical behaviors of MHBS during exploitation by thermal recovery and depressurization methods, a novel 2D thermo-hydro-mechanical bonded contact model was proposed and implemented into a platform of distinct element method (DEM), PFC2D. MHBS samples were first biaxially compressed to different deviator stress levels to model different in-situ stress conditions. With the deviator stress maintained at constant, the temperature was then raised to simulate the thermal recovery process or the pore water pressure (i.e. confining pressure for MH bond) was decreased to simulate the depressurization process. DEM simulation results showed that: during exploitation, the axial strain increased with the increase of temperature (in the thermal recovery method) or decrease of pore water pressure (in the depressurization method); sample collapsed during MH dissociation if the deviator stress applied was larger than the compression strength of a pure host sand sample; sample experienced volume contraction but its void ratio was slightly larger than the pure host sand sample at the same axial strain throughout the test. By comparison with the laboratory test results, the new model was validated to be capable of reproducing the exploitation process by thermal recovery and depressurization methods. In addition, some micro-scale parameters, such as contact distribution, bond distribution, and averaged pure rotation rate, were also analyzed to investigate their relationships with the macroscopic responses. 相似文献
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冻结砂土力学性质的离散元模拟 总被引：1，自引：0，他引：1
基于离散单元法颗粒流理论,土体颗粒单元间采用接触黏结模型中来考虑冻土中冰的胶结作用,建立了冻结砂土的颗粒流模型。通过改变计算模型中颗粒单元的参数,模拟了在不同冻结温度以及不同围压下冻结砂土的宏观力学性质,并与冻结砂土的室内试验结果进行了比较,结果表明：颗粒流方法可以较好地模拟冻结砂土的应力-应变关系以及剪切带的发展变化过程,颗粒流细观参数对温度具有显著的依赖性。研究结果对离散单元法在特殊土中的应用具有一定的理论和应用价值。 相似文献
8.
基于中主应力修正关系的边坡稳定性分析 总被引：1，自引：0，他引：1
边坡稳定性分析时通常将应力条件简化为平面应变状态,采用三轴试验强度计算出的边坡稳定性偏于保守。在充分考虑中主应力物理含义及力学机制的基础上,将Mises屈服准则与Mohr-Coulomb（简称M-C）内切圆屈服准则进行匹配,得到了平面应变条件下土体屈服破坏时中主应力的理论修正关系,进而也得到了该条件下最大主应力与最小主应力的比值关系,从理论上证明了该比值关系是与土体平面应变破坏时内摩擦角成一定关系的常数,也在平面应变试验中得到了验证,从侧面反映出中主应力理论修正关系的合理性。由上述两种关系建立了土体平面应变破坏条件下的应力路径,结合Lade-Duncan强度准则,建立了平面应变条件下强度参数与三轴试验试验条件下强度参数转换公式,由该转换公式得到的平面应变条件下的强度参数与平面应变试验实测值误差在2%左右,大幅缩小了三轴试验实测值与平面应变试验实测值的误差。在均质边坡稳定分析中分别采用常规三轴试验强度值与由公式转换得到的平面应变强度值进行计算。研究结果表明,三轴试验条件下内摩擦角为10°～20°之间时,基于两种强度参数得出的安全系数相差不大;当三轴试验条件下内摩擦角大于20°时,平面应变条件下安全系数较三轴试验条件下提高19%左右,但该成果只在文中计算案例有效,两者误差的准确关系还有待于进一步研究。值得关注的是,由于平面应变条件下土体强度变大,边坡的临界滑面深度变浅了,其形态相应变陡。 相似文献
9.
An Example of Realistic Modelling of Rock Dynamics Problems: FEM/DEM Simulation of Dynamic Brazilian Test on Barre Granite 总被引：2，自引：1，他引：1
The scope of this study is to numerically simulate the behaviour of Brazilian disc specimens as observed in laboratory during dynamic, high-strain rate, indirect tensile tests using an innovative combined finite-discrete element method (FEM/DEM) research code. Laboratory experiments using a split Hopkinson pressure bar (SHPB) apparatus were conducted by the authors and the measured indirect tensile strength values were used to verify the FEM/DEM models. In the models the applied boundary conditions, related to the loading rate of the specimen, were matched with the experimental observations. The results of the numerical simulations, including tensile strength and failure time, are in agreement with the laboratory findings. The main failure mechanisms, i.e. tensile splitting along loading axis and shear failure close to loading platens are captured by the numerical model. A linear relationship between tensile strength and loading rate is found for the range of dynamic strain rates tested and simulated. The simulation results are in good agreement with laboratory observations and demonstrate the potential for using FEM/DEM to realistically model dynamic response of rocks. 相似文献
10.
砂土中单桩竖向抗压承载机制的离散元分析 总被引：3，自引：0，他引：3
将单桩视为平面问题,采用二维离散单元法分析了砂土中单桩竖向抗压承载机制。首先利用离散元模拟地基的形成、挖孔灌注桩的成桩过程以及地基土的双轴压缩试验;然后通过离散元模拟单桩竖向抗压静载试验,分析其承载机制。结果表明：随着桩的沉降增大,桩端阻力一直增大,桩侧摩阻力先增大后达到稳定值;单位桩长侧摩阻力从桩顶到桩端呈非线性增长趋势;当荷载达到桩的极限承载力时,桩端发生刺入破坏,导致桩侧与桩端附近土体的转动场梯度、应力场梯度增大,主应力发生大角度旋转。 相似文献
11.
对基坑开挖影响范围内土体的应力路径进行平面应变试验离散元数值模拟,以研究结构性与卸荷形式对坑周土体宏微观力学特性的影响。首先,将一个描述土颗粒间胶结效应的简单三维胶结接触模型植入三维离散元软件PFC3D;其次,对初始K0固结状态的重塑土、结构性土试样分别进行常规三轴以及平面应变条件下4种不同卸荷应力路径的离散元模拟;最后,对经历不同卸荷形式的坑底土体单元进行再加荷模拟。模拟结果表明,在卸荷过程中,被动区土体峰值强度以及破坏时竖向应变随卸荷比增大而增大,且其强度小于主动区土体强度;在卸荷、再加荷过程中,被动区土体峰值强度随卸荷比增大而增大,但均小于不卸荷而直接加荷条件下的峰值强度;由于结构性的存在,土体由应变硬化向应变软化过渡,且强度增长;结构性与卸荷形式显著影响土体体积改变。在微观尺度,增大卸荷比或结构性均会增大垂直大主应力方向的平面上的法向接触力,进而提高其强度。 相似文献
12.
三维离散元单轴试验模拟甲烷水合物宏观三轴强度特性 总被引：1，自引：0，他引：1
填充型水合物的砂性能源土试样可视为特殊的散粒体材料,即砂粒和水合物颗粒混合物,具有明显的非连续特征。为研究填充型水合物的能源土力学特性,初步探索了甲烷水合物在不同温度、反压条件下加荷模式的离散元模拟方法。离散元模拟中,将水合物块体视为由大量颗粒通过强胶结作用凝聚而成的整体,室内试验中的内部孔隙水压作用转化为水合物颗粒间的胶结力,故需要合理确定颗粒间胶结模型参数来实现反压的影响作用。通过参数反演建立了宏观强度、刚度参数与平行胶结模型的微观胶结参数间的宏、微观关系,基于已有室内甲烷水合物三轴试验资料,确定了给定温度和反压条件下的微观胶结参数取值,随后进行离散元单轴压缩试验。离散元单轴压缩试验模拟获得的水合物强度特性,与室内三轴试验结果符合较好;通过建立的宏、微观参数间的关系,实现了不同温度、反压下的水合物加荷模式的模拟。为进一步提出深海能源土离散元数值试验成样方法--孔隙填充水合物生成技术,形成含填充型水合物的能源土试样,研究其力学和变形特性奠定基础。 相似文献
13.
堆石料大三轴试验的细观模拟 总被引：3，自引：0，他引：3
采用三维颗粒流计算程序,对堆石料的大三轴排水剪切试验过程进行了数值模拟。在数值模型的生成过程中,使堆石料集合体达到规定密度和级配;采用动态松弛算法迭代求解,并引入粒间阻尼,以吸收颗粒填装的多余动能使其稳定;颗粒间引入黏结力来提高试样的峰值强度;确定堆石料的细观力学参数,拟合室内试验应力应变曲线。模拟不同围压下堆石料的试验,得到的应力-应变曲线与室内试验基本一致,说明颗粒流方法可以较好的模拟堆石料的大三轴试验过程。由于没有考虑颗粒形状及颗粒破碎的影响,造成大应变剪胀偏大。 相似文献
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刚性桩复合地基抗震性能的振动台试验研究 总被引：3，自引：0，他引：3
为研究刚性桩复合地基的抗震性能,设计并完成了刚性桩复合地基1:10比尺的振动台试验。试验采用柔性容器这一较新的技术较好地模拟了地基在地震作用下的振动变形。此外,为解决模型与原型难以较好相似的问题,模型中尝试采用了在基础底板施加竖向力、在结构上附加阻尼器等措施。通过大量激振试验,对刚性桩复合地基的地震反应性态、柔性容器的效果等问题进行了研究。结果表明,柔性容器能够较好地解决模型试验的边界问题,刚性桩复合地基具有良好的抗震性能,桩身应变在地震作用下均未达到极限值,上部结构特性对桩身变形有一定影响,振动使土体对基础的约束减弱,但对桩的约束增强。 相似文献
17.
在传统的库伦土压力理论中,刚性挡墙后无粘性填土中的破裂面被假定为平面。然而,一些室内试验和现场测试结果均已证明了实际破裂面是曲面。以刚性挡墙后无粘性填土中的破裂面为研究对象,以竖向微分单元法为基础,利用变分原理推导了主、被动状态下关于破裂面曲线的微分方程,并对该方程进行了求解。研究结果表明,当墙背光滑或墙背与土体的摩擦系数为定值时,填土中的破裂面和破裂角均与库伦土压力理论相同;当墙背与填土的摩擦系数呈线性规律变化时,对应的破裂面为曲面。最后,讨论了墙背摩擦角和填土内摩擦角对破裂角的影响。 相似文献
18.
The concurrent multiscale method, which couples the discrete element method (DEM) for predicting the local micro‐scale evolution of the soil particle skeleton with the finite element method (FEM) for estimating the remaining macro‐scale continuum deformation, is a versatile tool for modeling the failure process of soil masses. This paper presents the separate edge coupling method, which is degenerated from the generalized bridging domain method and is good at eliminating spurious reflections that are induced by coupling models of different scales, to capture the granular behavior in the domain of interest and to coarsen the mesh to save computational cost in the remaining domain. Cundall non‐viscous damping was used as numerical damping to dissipate the kinetic energy for simulating static failure problems. The proposed coupled DEM–FEM scheme was adopted to model the wave propagation in a 1D steel bar, a soil slope because of the effect of a shallow foundation and a plane‐strain cone penetration test (CPT). The numerical results show that the separate edge coupling method is effective when it is adopted for a problem with Cundall non‐viscous damping; it qualitatively reproduces the failure process of the soil masses and is consistent with the full micro‐scale discrete element model. Stress discontinuity is found in the coupling domain. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
19.
平面应变仪是一种开发较早但至今尚不完善的一种土工试验仪器,随着国家基础设施建设的发展,平面应变试验及试验方法在许多领域得以应用,显示出了平面应变试验在工程设计和研究中的重要性。通过回顾国内外平面应变仪的发展,提出了开发一种新型的土工平面应变三轴仪的思路,以实现更科学、更精确地进行复杂应力加载条件下土平面应变试验的研究。以此为目的,从压力室结构、加载系统及控制量测系统等方面提出了相应的改善措施,开发了一种新型的土工平面三轴仪。并通过重塑黄土的平面应变试验及改进的真三轴仪平面应变试验对比、以及平面应变试验强度参数与常规三轴试验强度参数对比分析,验证了所研制的新型卧式土工平面应变仪的合理性和研制思路的正确性。最后,通过对该平面应变仪应变试验的黄土破坏特性与改进真三轴平面应变试验的黄土破坏特征的对比分析,验证了本文所开发的平面应变仪在描述土体应变局部化问题的合理性。 相似文献
20.
软黏土具有含水率高、压缩性强、泊松比大的物理特性。对于深厚软黏土地基而言,在竖向荷载的作用下很难保证侧向变形为0,适当考虑侧向变形的柔性约束条件可能更符合工程实际。因此,提出了柔性侧限条件下的竖向固结试验方法,对原状土样及重塑土样分别进行了不同侧向约束条件下的竖向固结对比试验,分析了侧限条件对软黏土沉降特征及变形参数的影响。试验成果表明,柔性侧限条件下土体的主固结变形量、次固结变形量均较K0侧限条件下的大,主固结完成时间较短,且等时曲线非线性化程度更高。基于试验成果及ε-lgp曲线,引入非达西渗流理论,对一维Terzaghi经典固结理论进行修正,建立了柔性侧限约束条件下的非线性控制方程,此计算模型参数通过柔性侧限固结试验获取,可计算一定侧向变形条件下土体的变形特性,通过对室内试验成果的模拟验证了模型的有效性。 相似文献