|Alternative Title||Research of Motion Process about Viscous Landslid-collapse Siol Based on PFC3D|
|Place of Conferral||北京|
|Keyword||岩土工程 山地灾害 粘性崩滑土体 运动过程 Pfc3d|
|Abstract||崩滑灾害分布广泛，危害严重，常威胁人民的生命和财产安全。目前，对崩滑失稳过程与机理研究较多，对其失稳后运动过程多以块体理论或流体理论，从宏观表象进行研究，少有学者根据崩滑土体内部物质组成，从细观角度分析研究崩滑土体运动过程，对于粘性填隙介质对崩滑土体运动过程影响更是未见相关研究探讨。对于崩滑土体失稳后形成的粗颗粒和粘性填隙介质组成的粘性崩滑土体，其运动过程复杂，开展有关粘性填隙介质对崩滑运动过程影响的力学机制问题、粘性填隙介质对崩滑运动过程形态、速度和冲击力的影响等问题的研究，对丰富崩滑灾害研究内容和崩滑灾害防治等具有重要的意义。因此，根据粘性崩滑土体物质组成，基于散粒体理论，从细观角度，以粗颗粒为对象，利用 PFC3D离散单元法，开展粘性崩滑土体运动力学机制分析、粘性填隙介质旋转剪切和拉伸实验、粘性崩滑土体运动数值仿真和物理模型实验等相关工作，分析粘性填隙介质对崩滑土体运动过程的影响，初步取得以下研究成果： 1）基于散粒体理论，粘性崩滑土体运动力学机制为颗粒碰撞和颗粒粘连；引用颗粒接触碰撞赫兹模型和颗粒粘连模型共同描述粘性崩滑土体运动过程 粘性崩滑土体可概化成粗颗粒与粘性填隙介质组成的混合体；粗颗粒与粘性填隙介质相互作用力学机制为粗颗粒与填隙介质的切向和法向粘连作用；粘性崩滑土体运动过程由颗粒碰撞和颗粒粘连两过程组成，可通过颗粒接触碰撞赫兹模型和颗粒粘连模型共同描述；粘性填隙介质的剪切强度、剪切刚度和法向粘连强度、法向粘连刚度为影响粘性崩滑土体运动过程的关键力学参数。 2）明确粘性填隙介质剪切强度、剪切刚度、拉伸强度和拉伸刚度等关键力学参数确定实验方法；构建粘性填隙介质剪切强度、剪切刚度、拉伸强度及拉伸刚度与粘性填隙介质密度关系式 将粘性崩滑土体运动过程中颗粒与填隙介质间的切向受力、法向受力过程概化成粗颗粒间全截面剪切过程和拉伸过程；粘性填隙介质剪切强度、剪切刚度、拉伸强度和拉伸刚度可通过旋转剪切和法向拉伸实验确定；根据粘性崩滑土体运动过程特点和粘性填隙介质剪切、拉伸实验结果，将粘性试样第二循环残余峰值剪切应力、峰值动力粘度作为相应密度成都粘土剪切强度和剪切刚度；将低拉伸速率（50μm/s）情况下最大法向拉应力作为相应密度成都粘土法向拉伸强度，通过应力应变关系确定其法向粘连刚度；实验结果表明：剪切强度、剪切刚度、法向粘连强度和法向粘连刚度随介质密度的增大而增大；法向粘连力随拉伸速度的增大而提高；粘连范围随密度的提高而增大；建立剪切应力、动力粘度与填隙介质含水率、剪切速率关系式。 3）基于商用PFC3D平台，编写粘性崩滑土体运动数值仿真程序，利用颗粒接触碰撞赫兹模型和颗粒粘连模型描述粘性填隙介质对崩滑土体运动过程；建立粘性崩滑土体内部细观参数（粘性填隙介质密度）与运动过程宏观表象（形态、速度和冲击力）间的联系，并通过同尺寸物理模型实验加以验证 编制PFC3D粘性崩滑土体运动数值仿真程序，生成粘性崩滑土体数值模型试样，根据剪切实验和拉伸实验结果，设置关键参数，开展粘性崩滑土体运动数值仿真实验，分析粘性填隙介质对崩滑运动形态、速度和冲击力的影响。结果表明：粗颗粒崩滑运动过程具有阶段性，即失稳-加速-堆积三阶段；颗粒速度峰值随粘性填隙介质密度增大而减小；随粘性填隙介质密度增大，崩滑运动过程形态由无粘溜砂形式向碰撞-粘连运动形式到整体块状形式转变；粘性填隙介质密度影响粘性崩滑土体对障碍物冲击过程和冲击力的大小，当粘性填隙介质密度大于1.413g/cm3后，崩滑冲击力迅速提高。 开展与数值仿真同尺寸物理模型实验，通过同工况坡面运动形态对比，对粘性崩滑土体运动PFC3D数值仿真结果进行检验，证实了PFC3D离散单元法在描述粘性崩滑运动过程的可行性。|
|Other Abstract||Slump disasters are widely distributed and often threaten people’s lives and property seriously. Currently, there are many researches about slum motion and mechanics whose instability is along sliding surface. And then multi-block theory and fluid theory is popular to study its process after lost stablity. However, there are little researches based on slump material composition especially the interstitial medium with meso analysis. Viscous slump motion process is complex. Viscous interstitial medium influence on its movement shape, speed and impact was the weak link. It is of great significance to carry out viscous slump soil movement study for disaster prevention. Based on analysis of current theory and material composition, this research paid attention to its mechanism and viscous interstitial medium influence. Taking coarse particles as object, the above problems were analyzed with granular theory and simulated by PFC3D. The preliminary results obtained as following:|
1）Based on granular theory, Hertz contact collision model and particle adhesion model were used to describe slump motion process and its mechanism were analyzed from meso-scale.
Viscous slump soil was generated as mixture of coarse particles and viscous interstitial medium. Its movement process was divided into particle collision and particle adhesion, respectively described by Hertz contact model and adhesion model on PFC3D. Moreover, the key parameters were also analyzed, providing basis for numerical simulation.
2) Identify the experimental methods of key parameters of slump motion such as shear strength, shear stiffness tensile strength and stiffness. This study also established the relationship between parameters and bulk density.
The tangential stress and normal stress between coarse particles and interstitial medium were turned to full section shear and tensile process separately. Tensile and shear experiments were carried out to get four parameters. According to movement characteristics analysis and experiments results, the peak shear stress and dynamic viscosity in second circle were chose as shear strength and stiffness. The maximum normal tensile stress at 50μm/s was chose as tensile strength. And tensile stiffness was determined by stress-strain curve. In the same time, this study established the relationship between parameters and bulk density. Results showed that the above four parameters improved with bulk density. The normal adhesion force improved with rate increasing and its adhesion range also expanded with bulk density increasing. The relationship between shear stress, dynamic viscosity, and moisture and shear rate was also established.
3) Through numerical simulation on commercial PFC3D platform, this study established the relationship between microscopic parameters (the bulk density of viscous interstitial medium) and slump motion macroscopic appearance (shape, speed and impact). In addition, the results were examined by the same scale physical model experiments.
By programming on PFC3D platform, the key parameter values were set by experiment results, and numerical simulation of viscous slump movement were carried out to analyze viscous interstitial medium bulk density influence on its movement shape, speed and impact. Results indicated that, inside particle movement characteristics of viscous slump soil are as following. It could be divided into three stages, namely instability- acceleration- accumulation. With the increase of medium density, the peak velocity decreased. However, the particle velocity fluctuation frequency and amplitude were greater than cohesion less condition. While the medium density increased, slump movement shape transferred from cohesion less sand-sliding to cohesion-adhesion movement and sliding along the slope as whole mass. When slump medium density was above 1.413 g/cm3, the impact improved rapidly with bulk density increasing.
With physical experiments of same size, the mechanism model and numerical simulation results were verified. Compared viscous slump slope movement shape in different conditions, the results showed that numerical simulation based on PFC3D could well reproduce its movement process.
|季宪军. 基于PFC3D粘性崩滑土体运动过程研究[D]. 北京. 中国科学院研究生院,2013.|
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