隧道砂卵石围岩离散元法细观参数计算方法研究

According to the particle property of the tunnel sandy-cobble surrounding rock, a particle discrete element method can better subtly simulate its instability process and its failure mode. However, the numerical value of microscopic parameter of discrete element method for the tunnel sandy-cobble surrounding rock has not been solved, and the calculation result can not be judged quantitatively. Therefore, this research aims to make calculation method research on microscopic parameter of discrete element method for the sandy-cobble rock surrounding of tunnel. To begin with, based on the particle discrete element method, this research constructs a tri-axial numerical experiment simulation platform which has the same full scale and loading method as the true tri-axial test of large-scaled coarse-grained soil; secondly, this research finds out the macro-mechanical parameter and the variation law of the microscopic structures under different compactness and water contents by means of selecting representative graded sandy-cobble surrounding rock of tunnel as the research object and employing large-scaled true tri-axial experiment; thirdly, based on the simulation platform of the tri-axial numerical value experiment, this research constructs a discrete element method model with the same structure as that in the true tri-axial experiment and discloses the influence rule of the microscopic parameter of discrete element method on the macro-mechanical parameter; finally, according to the results gained from said experiments, this research rationally determines the microscopic parameter of discrete element method for different microscopic structures; this research generates a set of microscopic parameter of discrete element method for microscopic structures with different particle gradations, compactness and water contents after theoretical analysis and provides necessary references for fined simulated microscopic parameter of discrete element model of the tunnel sandy-cobble surrounding rock.

针对隧道砂卵石围岩颗粒离散特性，采用颗粒离散元法更能精细化模拟其失稳过程及破坏模式，然而砂卵石围岩离散元细观参数取值问题尚未解决，计算结果无法定量判定，由此本项目拟对隧道砂卵石围岩离散元法细观参数计算方法进行研究。首先，基于颗粒离散元法，构建与大型粗粒土真三轴试验机足尺比例和加载方式相同的三轴数值试验模拟平台；其次，选择代表性级配砂卵石围岩为研究对象，采用大型真三轴试验，确定其不同密实度和含水量细观组构宏观力学参数及变化规律；然后，基于三轴数值试验模拟平台，建立与真三轴试验相同细观组构的砂卵石围岩离散元模型，揭示其离散元细观参数对宏观力学特性影响规律。最后，依据以上试验结果合理标定不同细观组构砂卵石围岩离散元模型细观参数，通过理论分析形成一套不同颗粒级配和密实度及不同含水量细观组构砂卵石围岩离散元法细观参数计算方法，为隧道砂卵石围岩离散元精细化模拟细观参数取值提供重要参考依据。

由于砂卵石围岩颗粒细观上的不连续性和非匀质性，其宏观力学行为受细观组构影响显著，当砂卵石围岩颗粒级配、密实度和含水量等不同时，其宏观物理力学参数各异，这对离散元模拟时准确的选取细观参数造成较大的困难。为确保构建的砂卵石围岩颗粒离散元模型能够较准确的反映其宏观物理力学行为，基于颗粒离散元法开展隧道砂卵石围岩离散元细观参数计算方法研究具有重要的理论意义。研究工作主要体现在以下几个方面： .（1）开发了颗粒离散元大型三轴数值试验模拟平台。基于颗粒离散元法，建立了与室内大型三轴试验机足尺比例和加载方式相同的三轴数值试验模拟平台。同时，构建了与大型真三轴试验细观组构相同的砂卵石围岩模型，开展三轴数值试验，整个实验过程中，通过控制上下两个刚性压盘移动速度模拟试样加载，圆筒轴向速度是由伺服机理自动控制，以保持常围压。数值三轴试验模拟平台采用了参数化语言程序编制，其加载方式和几何尺寸可以任意改变，可以开展各种工况下的砂卵石土数值三轴试验研究。.（2）揭示了隧道砂卵石围岩不同密实度和含水量细观组够宏观力学参数。针对成都地区砂卵石土的颗粒级配17组样本，采用统计分析的方法，确定具有代表性的砂卵石土颗粒级配。针对选取的砂卵石土代表性颗粒级配，进行实验室大三轴试验，获取该级配下不同含水率（1.5%、4%、6%、8.5%）和密实度（松散、中密和密实）情况下的应力应变关系、粘聚力和内摩擦角等宏观力学参数。.（3）明确了隧道砂卵石围岩离散元模型细观参数对宏观力学特性的影响规律。通过砂卵石土离散元三轴数值试验，揭示了孔隙率、摩擦系数、接触刚度以及刚度比等离散元模型细观参数对宏观力学特性影响规律，研究结果表明：接触刚度和摩擦系数对砂卵石土宏观力学参数影响较大，刚度比和孔隙率则影响较小。.（4）提出隧道砂卵石围岩离散元法细观参数计算方法。依据砂卵石围岩离散元模型细观参数对宏观力学特性影响规律，结合真三轴宏观力学参数研究成果，建立了不同含水率（1.5%、4%、6%、8.5%）和密实度（松散、中密和密实）砂卵石土颗粒离散元细观参数具体量值，同时也建立了砂卵石土颗粒离散元细观参数计算方法。