基于PFC^(3D)的黄土三轴试验细观参数敏感性分析

SENSITIVITY ANALYSIS OF MESO-PARAMETERS IN LOESS TRIAXIAL TEST BASED ON PFC^(3D)

从细观角度出发,研究各细观参数对黄土三轴试验宏观力学响应的影响,基于三维离散元PFC3D软件及理论,结合室内三轴试验结果确定数值模拟基本细观参数取值范围,在50 k Pa、100 k Pa、150 k Pa、200 k Pa围压下对三轴试样进行颗粒流模拟,通过改变各细观参数值对黄土数值试样宏观力学行为影响程度及正交试验设计的方式,开展黄土三轴数值模拟过程中摩擦系数、孔隙率、颗粒刚度比kn/ks、颗粒粒径分布的敏感性分析,建立土体细观参数与宏观力学的关系式。结果表明:不同围压下数值试样峰值强度和剩余强度均与摩擦系数正相关,与颗粒刚度比、孔隙率负相关,而颗粒粒径分布的变化对其影响均小于2%。低围压下(50 k Pa),孔隙率对数值试样峰值抗剪强度和剩余强度影响最大,颗粒刚度比次之,高围压下(200 k Pa),摩擦系数对数值试样强度的影响比颗粒刚度比更为显著;对数值试样的初始线弹性模量和应变软化特性影响最大的细观参数为孔隙率,刚度比次之,颗粒粒径分布最小,200 k Pa围压下正交试验分析结果与数值分析结果一致。通过改变细观参数取值范围的方式系统地分析了其对黄土三轴试验宏观力学性能的影响,为今后离散元软件用于黄土室内试验研究提供了参考。

The influence of meso-parameters on macro-mechanical response of loess in triaxial test is studied from meso-perspective.Based on the PFC3D software and the results of the indoor triaxial test to determine the value range of the basic mesoscopic parameters of the numerical simulation,particle flow simulation of triaxial samples is performed under the confining pressures 50 kPa,100 kPa,150 kPa,and 200 kPa.By changing the influence degree of mesoscopic parameters on the macroscopic mechanical behavior of loess numerical samples and orthogonal test design,the sensitivity analysis of friction coefficient,porosity,particle stiffness ratio kn/ksand particle size distribution in the process of loess triaxial numerical simulation is carried out,and the relationship between soil mesoscopic parameters and macroscopic mechanics is established.The results show that the peak strength and residual strength of the numerical samples under different confining pressures are positively correlated with the friction coefficient,and negatively correlated with the particle stiffness ratio and porosity.The influence of particle size distribution on it is less than 2%.Under low confining pressure(50 k Pa),porosity has the greatest impact on the peak shear strength and residual strength of numerical samples,followed by particle stiffness ratio kn/ks,and under high confining pressure(200 kPa),the influence of friction coefficient on the strength of numerical sample is more significant than that of particle stiffness ratio.The meso-parameters that have the greatest impact on the initial linear elastic modulus and strain softening characteristics of the numerical sample are porosity,followed by the stiffness ratio kn/ks,and the particle size distribution is the smallest.The result of orthogonal test under 200 k Pa confining pressure is consistent with the result of numerical analysis.By changing the value range of mesoparameters,the influence on the macro-mechanical properties of the loess triaxial test is systematically analyzed,which provides a reference for the future use of discrete element software in loess laboratory test research.