摘要
花岗岩残积土中粗粒的几何形态特征对其工程力学性质有显著的影响,逐一精准定量表征土体中土颗粒的真实复杂形状一直是困扰此类土体本构模型及数值模型相关研究的主要难题之一。基于统计力学的方法从土颗粒看似杂乱无章无规律的几何特征中寻找统计规律,首先通过显微光学成像、数字图像处理等方法获取4个粒组大量粗粒的最大投影轮廓,其次运用快速傅里叶变换(FFT)方法求得粗粒几何形态的归一化Fourier描述子D n,随后根据幅度C n和相位角φn可精确重构颗粒轮廓,并且通过改变相位φn还可实现具有相似形态特征颗粒轮廓的随机生成。在此基础之上分析粗粒几何形态的统计力学规律,定量表征华南地区花岗岩残积土中四个粒径区间粗粒的平均伸长率、棱角度、表面纹理等几何形态特征,最后分析讨论了花岗岩残积土中粗粒的Fourier描述子与粒径之间的关系,及其与冲积河砂、滨海石英砂中粗粒几何形态参数的差别。根据对比结果发现:首先,无论是残积土还是冲积土,0.5~1.0 mm粗粒的D 2最大,5~10 mm粗粒的D 2-D 8最小,说明粗粒粒径越大,颗粒的规则程度越高。其次,与冲积河砂、海砂中的粗粒相比,花岗岩残积土中各粒径区间粗粒反映表面粗糙程度等细微观特征的D n(n>8)值基本相近,与其未经历过长期的搬运作用有关。冲积河砂中粒径较大粗粒多为岩石碎屑,矿物组成以角闪石、绿帘石为主,D n(n>8)值较低,说明其在搬运过程中被磨圆,降低了表面粗糙程度,而0.5~1.0 mm粒组的D n(n>8)值与花岗岩残积土各粒组的基本相同,表面粗糙程度都较高,这与二者粗粒中石英含量较高有关,说明石英颗粒在搬运过程中会发生断裂破坏从大颗粒破碎为小颗粒,但其表面不会被磨圆,而且土颗粒的几何形态特征受到了颗粒矿物组成的影响。最后还发现花岗岩残积土、冲积河砂及海砂中粗颗粒轮廓的D n与频率序列在双对数坐标log 2 D n-log 2 n中均呈线性关系,并统计了不同种类土的模型参数从而实现对不同类型土中粗粒轮廓几何形态的定量化表征,为之后粗颗粒离散元建模奠定了基础。
The morphological characteristics of coarse grains of residual granite soils have a significant impact on their engineering mechanical properties.However,accurately and quantitatively characterizing the real and complex shapes of soil particles one by one has always been one of the main difficulties in the study of constitutive models and numerical models.To find statistical laws from disordered and irregular geometric characteristics of soil particles seemingly based on statistical mechanics,the maximum projection profile of extensive coarse particles in four grain groups was obtained by means of optical microscopy and digital image processing,and then using Fast Fourier Transform(FFT)method to obtain Fourier descriptors D n,which contains all the morphological information of particle contour.The particle profile can be reconstructed accurately and randomly with amplitude C n and phaseφn.On the basis of analyzing the statistical mechanics law of particle geometry,the geometrical morphology of coarse grains,including mean elongation,angularity and surface texture,was quantitatively described for residual granite soils in South China in four particle size intervals.Finally,the difference of grain morphological parameters between undisturbed residual granite soil,alluvial river sands and offshore alluvial quartz sands was discussed.The results show that D 2 of 0.5-1.0 mm coarse grains is the largest and D 2-D 8 of 5-10 mm coarse grains is the smallest,which means that the larger the coarse particle size of residual soil or alluvial soil is,the higher the regularity of the particles is.Compared with the coarse grains in alluvial river sands and sea sands,the values of D n(n>8)reflecting meso-and micro-scopic characteristics of grain surface roughness in each grain size range of granite residual soil are basically similar,for having not experienced long-term transportation.The larger coarse grains in alluvial sands with low values of D n(n>8)are mostly rock debris,and the mineral components are mainly amphibole and epidote.This indicates that they are rounded in the process of transportation,which reduces the degree of surface roughness.However,the value of D n(n>8)of 0.5-1.0 mm granular group is basically the same as that of each granular group of granite residual soil,and the surface roughness is higher,which is related to the higher quartz content in the coarse grains of the two groups.This indicates that the fracture and destruction of quartz particles will occur in the process of transportation.The particles are broken into small ones,but their surface will not be ground round.And the geometric characteristics of soil particles are affected by the mineral composition of particles.A linear relationship between log(D n)and log(n)is found in double logarithmic coordinates.The model parameters of different kinds of soils are calculated to characterize the geometrical shape of coarse particles in different types of soils quantitatively,which lays a foundation for the subsequent discrete element modeling of coarse particles.
作者
徐长文
刘锋涛
张澄博
高燕
XU Changwen;LIU Fengtao;ZHANG Chengbo;GAO Yan(School of Geoscience and Engineering,Sun Yat-sen University,Zhuhai 519000,China;Key Laboratory of Geodynamic Action and Geological Hazards in Guangdong Province,Guangzhou 510275,China)
出处
《中山大学学报（自然科学版）》
CAS
CSCD
北大核心
2019年第6期45-55,共11页
Acta Scientiarum Naturalium Universitatis Sunyatseni
基金
广州市科技计划项目(201707010082)
广东省自然科学基金项目(2018A030313897)
